Color Encyclopedia of Gemstones

SECOND

EDITION

COLOR

NCYCLOPED1A OF

JOEL E AREM, PHD, FG. A.

COLOR iNCYCLOPEDIA

SECOND

JOEL Since

E.

EDITION

AREM,

PH.D., FG.A.

gem

gemologists,

1977,

jewelers, and

gem

collectors,

dealers have relied on

acclaimed sourcebook for immediate

this

information on gems. updated and revised, Color Encyclopedia of Gemstones Second Edition, is the most complete and comprehensive tabulation ever available on the properties of all known gemstone species and varieties. access

Now

essential

to

fully

,

With speed and convenience, the Encyclopedia will direct you to concise and accurate data on

particular

a

ability,

rarity,

book's

the

graphs

gems

gemstone's physical chemistry,

occurrence,

properties,

and market potential. And

spectacular

— over

300 are

that

avail-

in

photo-

full-color

all

—

many

illustrate

depicted

no

in

other

gemstone book.

A

major feature of

the

new coverage

this

second edition

is

of synthetic gems. In this

section you will find complete data on

all

the important synthetic materials, including those with and without natural counter-

There is also information on some of the more unusual synthetics some hardly ever encountered as cut gems and parts.

—

therefore posing serious identification prob-

lems.

And

the introductory material to this

section clarifies for the

the

definitions

true

of

first

time

in print

"synthetic"

and

"homocreate" materials, bringing gemology into line with internationally accepted nomenclature standards. Diagrams of the important crystal growth methods and descriptions of how they work round out the wealth of coverage on synthetics available to

you here.

Also of special interest, and edition,

is

new

to

this

a detailed analysis of color

and

measurement as applied to gemstones. Here the author presents a com-

color

prehensive

listing

of machine-generated (Continued

•>

<,\kflap)

A VAN NOSTRAND REINHOLD BOOK

SAUSALITO PUBLIC LIBRARY 3 1111

For Reference Not to be taken from

this

room

01084

102

COLOR ENCYCLOPEDIA OF GEMSTONES

COLOR ENCYCLOPEDIA OF GEMSTONES Second Edition

Joel E.

VHE

Arem, Ph.D.,

EGA.

VAN NOSTRAND REINHOLD COMPANY New c

York

Sausalito Public Library i:*~ r~\:t*~*\~ Oaoas

This book

New

is

dedicated to

Abraham "Edge" Goldstein of Brooklyn, gems and his generosity and

York. His love of minerals and

willingness to share his

knowledge with others have been an

tion to three generations of hobbyists. to

Copyright

©

1977, 1987 by

be numbered

among

those

Van Most rand Reinhold Company

Inc.

photographs copyright © 1977, 1987 by Joel E. Arem Library of Congress Catalog Card Number: 86-26759 ISBN: 0-442-20833-2 All rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means— graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage and retrieval systems— without written permission of the publisher.

America

Van Nostrand Reinhold Company 115 Fifth Avenue

New

York,

New York

Inc.

10003

Van Nostrand Reinhold Company Limited Molly Millars Lane

Wokingham, Berkshire RG11 2PY, England Van Nostrand Reinhold 480 La Trobe Street Melbourne, Victoria 3000, Australia Macmillan of Canada

Canada Publishing Corporation 164 Commander Boulevard Agincourt, Ontario MIS 3C7, Canada

Division of

16

15

14

13

12

11

10

9

8

7

6

5

4

Library of Congress Cataloging-in-Publication Data Arem, Joel E., 1943-

Color encyclopedia of gemstones. Bibliography: p. Includes index. 1.

Precious stones.

QE392.A69 1987 ISBN 0-442-20833-2

I.

Title.

553.8 '03 '21

86-26759

3

2

inspira-

consider myself fortunate

whom Edge considers his close friends.

All

Printed in the United States of

I

1

Contents

Preface

vi

I

Acknowledgment

I

viii

INTRODUCTION What

/

Gem?

a

/

Scope of This Book

/

Is

The Nature

Gems

of

GEM SECTION

1

2

GEMSTONES FROM THE LABORATORY

3 4

/

History

Crystal Structures and Properties

Origin of

Gemstones

Rock

Classification

Gem

Scarcity

Intrusive

Crystal

6

Growth

Synthetic

Gem

9

/

Gemstones

SOURCES OF DATA USED

TRADE NAMES OF SYNTHETICS BIBLIOGRAPHY

10

/

Crystallography

TEXT

/

13

236

/ /

/

237

237

/

238 238

GEMSTONE SPECIES AND ORNAMENTAL MATERIALS

16 16

239

/

18

/

19

/

Luminescence Occurrence / Stone Sizes

233

15 /

Comments

/

Journals

14

/

Inclusions

Jewelry

Synthetics

14

Spectral

13

/

/

236 236 237 /

Mineralogy

/

Cleavage Optics /

/

/

Diamonds Specific Gemstones

14

/

Density

IN

13

/

Hardness

220

HOMOCREATE MATERIALS THAT HAVE BEEN SYNTHESIZED / 232

General

Luster

/

9

/

/

218

/

Listing

9

Identification of

Color

212

/

217

/

Characteristics

Sedimentary Rocks / 9 Sedimentary Features / 10 Metamorphic Rocks / 10

Formula

211

/

Definitions

9

/

Extrusive

4

8

/

Rock Types / Igneous Rocks

/

/

6

/

37

/

MINERAL GROUPS OF GEMOLOGICAL 19

/

INTEREST

/

241

19

/

19

/

20

REFRACTIVE INDEX GRAPH

THERMAL PROPERTIES

/

21

PERIODIC CLASSIFICATION OF

THE ELEMENTS

COLOR MEASUREMENT AND SPECIFICATION

/

25

/

INDEX

/

244

/

243

242

/

211

Preface

The

first edition of this encyclopedia was published a decade ago, and some remarkable changes have occurred in the gemstone marketplace during this interval. Although diamond still retains its place as the most popular and esteemed of all gemstones, the extremely wide gap in

this leadership position versus

rowed. There

is

a large

deposits, including

material.

diamonds (in truth, colored gemstones) may well become the most eagerly sought and highly prized of

book

is

all

gems before

the next edition of this

published.

The growing popularity of colored gemstones has made it crucial that a sensible, scientific, precise, consis-

colored stones has nar-

and growing demand

some extraordinary pink

So-called fancy colored

for all kinds

and universally accepted method of color grading

of gemstones, especially brightly colored stones that can

tent,

be worn as fashion accessories. Beaded jewelry has become an item of immense popularity; pearls have seen a huge

be developed.

The immense pool

of capital in pension

plans and trust accounts will never touch

Rare gemstones such as tanzanite and tsavorite have made the transition from collector items to market staples. Even such barely commercial stones as andalusite, iolite, sphene, chrysoberyl, and some of the feldspars are becoming more widely known and distributed. The long-speculated and long-awaited birth of a large and active collector market for gemstones cannot be far off. About thirty new species may now be added to the list of cut gems, along with some new varieties, such as malaya garnet. Previously unknown localities have yielded large and spectacular crystals of rare species, such as anglesite, which in turn have yielded record-size faceted gemstones. More and more dealers are aware of the growing value of exotic gem species; the list of known taaffeites has thus grown from a handful of gems to perhaps more than fifty known cut stones, and more will surely be identified. On the commercial side, the Argyle deposits of Australia have become the most important diamond discoveries of the century, adding as much as 50 percent to the proven world reserve of diamond. Unfortunately, most of

preservation vehicles until such grading

revival.

fact.

Many

gems as wealth-

is

an established

grading systems have been proposed. All of

them, without exception, have the same basic failing, that is, despite the pseudo-scientific appearance of "number systems" for estimating color,

clarity, cut,

and so

based on visual estimation. This is also true of diamond, an amazing fact considering that a multimillion dollar investment market rose and fell based forth, they are

all

on "certification' with a 20-30 percent. Large

built-in variability as high as

money

pools will never be invested any product that must be defined in such loose terms, with the consequent potential for immediate loss on liquidation as large as the upper end of the range of in

grading error.

Only objective,

scientific,

machine-based grading will

solve this problem. This implies the acceptance by the

gemstone in

field of

terminology that

other industries where color

textiles, plastics),

is

is

universally applied

equally important (paints,

such as Munsell color designations.

Also, the variability of color grading by such machines

must be reduced

diamonds are not suitable for cutting as gems, so while the amount of diamond in these deposits is immense, the total value is not as large as might be guessed. However, there seems to be an unusually high percentage of brightly colored diamond in the Australian the Australian

to less than 5 percent, a formidable

challenge indeed considering the complexity of measur-

where pleochroism, cutting proand inclusion-scattering are all potential sources

ing color in materials portions,

of error.

The gemstone

VI

field is also continually

searching for

PREFACE new, useful, simple, and nondestructive methods of ing. It

is

considerable development

likely that

cur during the next decade

in

test-

will oc-

perfecting both luster-

measurement systems (which obviate the problem of measuring high refractive indices) and thermal measurement devices, which blazed to prominence as a means of rapidly distinguishing between diamond and cubic zirconia. Synthetic gems have become a fact of life in the gemstone trade. In fact, most people associate the name spinel with birthstone simulants

and do not even

made of synthetic spinel

realize that natural spinels are rare,

durable, and beautiful gems. Synthetic ruby, emerald,

and sapphire have become important marketplace commodities in their own right and have a bright future. For as gemstones become increasingly rare and demand for them grows, gemstone prices will rise to a point where very fine stones are out of reach of

all

but a tiny percent-

age of potential buyers. Synthetic gems provide the look

and durability of these

fine, rare

gems

at a fraction of

their cost. Unfortunately, the crystal growers are enticed

by a far greater monetary reward than are the tists

who

gem

scien-

build detection equipment. Inevitably, a small

percentage of laboratories.

artificial

gemstones

The markets will

will foil

even the best

not be disrupted as long as

this

percentage remains small. Also, the physical proper-

ties

of most synthetic

gems

are within (or overlap) the

range of properties of their natural counterparts; detection

is

sions,

therefore based primarily on characteristic inclu-

some

of which are definitive proof of origin. Thus,

although a high degree of internal perfection adds measurably to the value of a gemstone, total perfection can be a real liability in the case of emerald and

gems. That origin of a

is,

corundum

small, hard-to-see inclusions allow the

gemstone

to be proven; a truly flawless

gem-

may be extremely rare and potentially valuable, may also be impossible to prove as natural!

stone

but

Laboratory products such as cubic zirconia have established markets of their tive

own, apart from and not competi-

with those for natural stones. Such products are

popular because we

live in an age of aspiration, where dramas about wealth and power have the highest ratings, an age where the trappings of wealth have mass appeal. Gemstones have long been used as a means of displaying affluence, and it is therefore not surprising

television

that the

demand

for

supply continues to

gems continues

fall.

to rise while the

The new

section on synthetic

cially timely. Synthetic

place for

some time

(in

century) and have caused

A number

gem

materials

gems have been

in the

the case of ruby

VII

is

espe-

market-

more than a

much confusion and concern.

of excellent books have been published on

synthetic gemstones, but they

all

seem

to focus

on the

technology and history of these materials. The chapter

on synthetics in this second edition is designed primarily to be useful to gemologists. The information is presented in the same format as for natural gemstones and summarizes the essential literature on the subject. The reader is referred to the books listed in the bibliography for details of manufacturing methods, history, and so forth. Also, the entire subject of gemstone treatment (color alteration and enhancement) is left for other texts. There is little doubt that many superb, large, and unique gemstones exist that have not been mentioned in the current work, despite a major effort to keep abreast of the appearance of such gems. Many of the cutters who produce these rare objects do not keep detailed notes, and once they have been spirited away into private or museum collections, it becomes enormously difficult to track them all down. A plea is once again extended to readers of this book to supply me with any information that will make future editions more comprehensive, accurate, and useful; thanks are gratefully extended to those individuals who took the time to comment on the first edition with the aim of helping to make future editions better. Some of the comments received as long ago as 1977 have finally been incorporated into this current work. It is my hope that the Color Encyclopedia of Gemstones will increasingly become the most-used handbook for quickly needed information about gemstones, as well as the text most used by an increasingly large and active group of gemstone collectors who are fascinated by the range of color and beauty displayed by many rare gemstone species and varieties. If these collectors play an active role in providing a continuing stream of information and comments about the book, it will then be ever more useful to those who need it most and who will shape the gemstone market of the future.

JOEL P.O.

E.

AREM

Box 5056

Laytonsville,

MD

20879

Acknowledgment

Many people

assisted in the production of the first ediColor tion of the Encyclopedia of Gemstones. Many of these people also assisted in the preparation of this revision, as did a number of other friends and colleagues. Those involved in the first edition include Floyd Beattie, Casper Beesley, Karen Breau, Bernard Cirlin, Carlton Davis, Denver Museum of Natural History, William Dippel, Pete J. Dunn, Mike Evick, Gemological Institute of America, A. Edge Goldstein, Alberta Gordon, Elvis Gray, Mike Gray, A. V. Gumuchian, George Harlow, John Holcombe, William T. Huff, Kuhn's Baltic Amber Specialties, William Larson, Jim Leone, Richard T. Liddicoat, Betty Llewellyn, Joseph Longstreth, Barry Nathan, C. D. ("Dee") Parsons, William Pinch, John Saul, Sonja Schwartzman, John Sinkankas, Kenneth Sumner, Lillian Turner, Martin Zinn.

who

some way with the second edition: Cos Altobelli, Jean DeMouthe, Ernest Fairbanks, Gordon V. Axon, Myrtle Granger, George Bruce, Bart Cannon, Charles Leavitt, Jr., W. W. Hanneman, Thanks

Don

to those

Hoover, Arthur

T

assisted in

Grant, Grant Waite, Michael

O'Donoghue, Peter Keller, Victor Yount, Eugene S. Love, Sean Sweeney, David Brackna, Richard E. McCarty, John T. McCasland, Thomas Chatham, and Sarabeth Koethe. Very special thanks are extended to C. D. ("Dee") Parsons, master cutter and collector extraordinaire,

who

assembled a unique collection of rare species and catseye gems for shipment to the author to be photographed for the second edition. This irreplaceable package was lost in the U.S. mail.

ration of the

Dee's invaluable assistance

possible for

many gem

color for the

first

I

am grateful

in the

edition of the encyclopedia

first

prepa-

made

species to be photographed

it

in

time.

to the

Minolta Camera Corp. for provid-

ing the superb diagrams reproduced in the section

on

color measurement technology.

welcome comments, criticisms, additions, and corhope of making future editions of this book more accurate, comprehensive, and useful. Please address all correspondence to Dr. Joel E. Arem, RO. Box I

rections in the

5056, Laytonsville,

MD 20879.

Introduction

Gemstones are among humans' most treasured objects. They have been held in high esteem throughout history by all societies in all parts of the world. The histories of

as recently as 1910 the nature of the internal structure of

certain individual gemstones can be traced over a span

the years following 1914, mineralogy, chemistry, and gem-

gems have

of centuries, and

the

same

associations of

wealth, prestige, status, and power as gold and In the earliest periods of civilization, people

silver.

became

curious about natural objects, including minerals. Minerals are naturally occurring inorganic

chemical elements

and compounds.

amended

Scientists today have

this defi-

nition in light of discoveries about the arrangements of

atoms

in crystals.

defined

in

A

mineral species

is

therefore also

terms of a definite crystalline structure.

The

chemical composition of a mineral may vary but only within defined limits. If the composition varies outside these defined limits, the mineral may be given a new name and considered a distinct species. Early humans discovered pebbles and fragments of various brightly colored minerals in fields and stream beds, on mountain slopes, and in barren deserts.

made

Some of

were ascribed mystical powers or symbolic religious significance. For centuries gem materials held a position of tremendous influence in human affairs. However, there was no science of gemology. The primary attribute of any gemstone was color, yet no reliable ways existed for differentiating these were

into ornaments. Others

minerals of the same or similar colors.

It is

not surprising

and the hundreds of references

crystals

was not firmly established.

When

X-rays

first

revealed the magnificent atomic geometry of crystals

ology

all

entered a

new age

in

of sophistication.

Progress, however, often adds complications and prob-

lems. At the

same time

that

some

scientists

worked

to

improve identification methods, others developed ways of duplicating nature s gem masterpieces in the laboratory. Accurate detection technology was, in a sense, developed just in time to prevent collapse of the market for various gemstones.

A

large part of the value of a fine

gem

lies in its

scarcity as a rare natural object. People are therefore less

spend a large sum of money for a stone that might turn out to be a laboratory product. The overall likely to

question of the reasons for the value of gems

is complex and will be discussed in following pages. Gemology, in the last decades of the twentieth century, is at a major turning point in its growth. Worldwide affluence has created an unprecedented demand for

gems

of fine quality, vastly raising their cost. Political

problems

in

gem-producing areas have created

tions in the supply of prices. Synthesis

gem

restric-

materials, further raising

technology

gem

developing new materials

is

with very desirable properties that are never found nature, as well as laboratory equivalents of the

become

in

more

that confusion reigned in both the literature

valuable natural gemstones.

marketplace. There are

devise ways to distinguish natural and synthetic materi-

literally

gemstones in the Bible. Yet in many cases it is not known today exactly what stones were being described. Some incorrect names that were in use nearly two thouto

sand years ago are

still

employed today!

The modern science of gemology

is

a relatively recent

development. Fairly accurate methods of chemical analysis existed more than one hundred years ago. Yet even

It

has

essential to

simulations and methods of color enhancement by chemical and physical treatment. This book is an encyclopedia of gemstones. It is an als as well to as reveal

attempt to provide basic information about eral species that

all the minhave been cut as gems, including their

color varieties. This introduction must

speak to the most basic question

at

hand:

first,

What

however, is

a

gem?

INTRODUCTION WHAT

A

IS

GEM?

cut blue zoisite resembles fine sapphire,

dubbed

the

new

material tanzanite and launched a major promotion of

World literature abounds with references to precious and semiprecious gems. These terms are used even today, without rigor, by the public and jewelry trade alike. Just what do these terms mean? In antiquity, the so-called precious stones were diamond, ruby, emerald, sapphire, pearl, and occasionally opal.

The

dictionary (Webster's New Collegiate Dictionary;

7th ed., 1967) defines precious as "of great value or high price"; semiprecious

is

defined as meaning "of less com-

mercial value than precious". a marketing worth noting as little as $200 per

This indicates clearly that precious term, applying to any expensive item. that a

diamond can be purchased

for

is

It is

"new gemstone." Today, tanzanite

accepted as a Here is an example of a mineral that was not a gem by accepted criteria before 1967 but became a gem by promotion. This is a double standard that leads one to ask for an objective criterion in the definition of a gem. The dictionary is again consulted, and we find that a gem is "a precious or sometimes semiprecious stone cut and polished for ornament." If we omit the terms relating to price, as discussed earlier, we have the basis of a simple and unambiguous definition. the

gem and

is

large stones bring rather high prices.

A gem is any mineral cut and polished for ornamental purposes.

carat, yet certain colors of garnet are currently selling at

prices over $1 ,000 per carat. Garnet has always been regarded as semiprecious, so it is obvious that these terms, as applied to gems, have little relevance or meaning.

Therefore, aside from considerations of historical usage, the terms precious and semiprecious should be pletely

We a

com-

abandoned. are

gem? Nobody

still left

with the fundamental issue:

What

is

argue with the statement that diamond, and emerald are gems. Opal is a gem, as are jade, lapis, garnets, and turquoise. However, what do we do with andalusite, diopside, and sphene? A material, to be considered a gem, must have beauty, durability, and scarcity, according to most accepted authorities, but all of these terms are subjective and open to wide interpretation. Opal, a gem, has hardness of only 5.5 on Mohs' scale (see page 15), which is really too soft to wear in a ring. Opal is also quite fragile and brittle and may crack spontaneously because of internal dehydration. If durability is a major criterion, opal is not a very good gem. Yet it is a gem and has always been considered as such because of its other properties and beauty. will

ruby, sapphire,

Proustite, a silver arsenic sulfide,

is

a rare mineral that

seldom faceted, and then only for collectors. Its red color is one of the richest in the mineral kingdom, far surpassing in intensity the hue of most rubies. Anyone who sees a cut proustite is likely to comment on its great beauty. There may be fewer than fifty cut proustites in is

the entire world, so the scarcity factor

gem or not? been known as a

is

indisputable. Is

a cut proustite a

Zoisite has

usually gray or pinkish

mineral for decades.

and opaque and seldom

by collectors of the unusual.

Then

in the late

It is

cut, even

1960s fine,

were discovered in Tanzania, and a few stones were cut from them. The cut stones were sold to a few collectors and connoisseurs of unusual faceted minerals. Eventually one of the world's major jewelry establishments. Tiffany & Co., noted that blue-violet, transparent zoisite crystals

There are more than three thousand known minerals. of them could be used as a gem if it were found in a form solid, massive, or attractive enough to warrant the effort of cutting. The definition of a mineral is unambiguous. The definition allows for all the rare and unusual materials that have been cut and that heretofore have been difficult to classify or discuss. My definition of a gem is thus very tight, but we must allow for several exceptions, which are considered gems through the necessity of thousands of years of acceptance as such. These exceptions are pearl, coral, and amber. Pearl and coral actually are made up of mineral material (calcite and aragonite) but created through the agency of organic

Any

processes.

Amber is the petrified, hardened sap of ancient

pine trees and

is

an organic material.

The term ornamental material could be more aptly applied to amber and coral, as well as ivory, jet, shell, and wood. All of these are natural materials of organic origin that are polished and used in jewelry, but they would not be called gems under the proposed terminology. A problem in nomenclature now arises regarding manufactured compounds and crystals that are sometimes cut for jewelry purposes. The term synthetic is derived from words that mean, literally, put together (from components), which, by itself, is noncommittal as to origin. The terms created and cultured have also been used in regard to laboratory products.

accept the term synthetic

The

public has

come

to

connection with jewelry stones created in the laboratory. It should always be remembered, however, that a synthetic gemstone is a contradiction

in

mineral, which

The

is

in

terms, since a

gem

is

by definition a

a naturally occurring material.

following classification avoids the confusions of

gem is a mineral cut and polished for ornamental use; a gemstone is a crystal, fragment, or pebble of gem material (this term is also used to describe the cut stone); a jewel is a combination of gemstone and metal setting allowing the gem to be worn easily; a current usage: a

SCOPE OF THIS BOOK synthetic

may

a manufactured material that

is

either be

physically and chemically equivalent to a mineral, or a

compound unknown

nature but that can be grown

in

transparent crystals suitable for cutting; a simulant material that resembles another (usually

more

is

in

a

costly)

material (for example, glass used as a substitute for ruby

or emerald).

A homocreate is a manufactured

with properties

in

natural substance

substance

the range of those displayed by the it

is

intended to duplicate; that

homocreate is a synthetic that specifically and chemically equivalent to a mineral.

is

is,

a

physically

works in the mineralogical and gemological literature. These provided a framework of basic information about all the species covered. Gaps were then filled by research into the periodical literature of mineralogy and gemology. This yielded current information about localities, new gemstones, additional basic data, and some information on gemstone sizes. In some cases, as in the case of dispersion, mineralogical data were reworked into a form more familiar to the gemologist. Specifically, a Hartman dispersion net was used to plot refractive index vs. wavelength information, and the interval B-G was extracted and reported as the dispersion of the material in

SCOPE OF THIS BOOK

question.

Spectral data are provided only where a spectrum

is

vide history and lore of stones, descriptions of occur-

enough to be useful in identification. Some spectra are complex and variable for a given mineral species, and in such cases the text lists only the pervasive

rences, mining and cutting techniques, or market and

or especially diagnostic

distinctive

Unlike other books about gems,

this

compendium

pro-

com-

of data organized in a format

These sources include the standard literature, specialized books on specific gems (such as amber, pearl, opal, and diamond) and personal communications from cutters, dealers, collectors, and museum curators. There

It is,

rather, a

that provides rapid access to the basic properties of

gemstones, especially those data that would be useful in identification.

The book's major asset is the large array of color The photographs are a result of nearly fifteen

plates.

years of concentrated effort to develop specific tech-

niques for gem photography. The ultimate goal is to capture on film the exact color of a faceted gemstone, while displaying to best advantage the cut and brilliance derived from the cutting. At the same time, hot spots or specular reflections from individual facets must be avoided,

and the gem as pictured should have solidity and dimension, rather than appear flat or look like a painting. It is a major photographic challenge to achieve all these features simultaneously. The color plates in this book represent

my current stage of technical competence, as modified

by the limitations of converting color transparencies to images on paper, and there is considerable room for

improvement. In many cases, however, the photos clearly of birefringence in a gem and also inclusions that are present, making the photos especially useful to the gemologist concerned with such matters. There are nearly 250 species included in this volume. It must be remembered, of course, that any mineral species can be considered a gemstone if suitable cutting material can be found. Some minerals have been known for decades or centuries but have not been considered

show the degree

gem

materials because pieces of sufficient size, cohe-

been available. This any time with respect to a given of gem species will undoubtedly

sion, or transparency have never

situation

may change

mineral, so the

list

lines.

Information on stone sizes comes from diverse sources.

price data that are rapidly outdated.

prehensive

work does not

at

are sure to be omissions in noting the existence of large

and important gems, for which I assume full responsibility. Such omissions can be eliminated in future editions through the assistance of readers of this book in sending me relevant information (see page vii). Information on wearing characteristics of gems is inferred from analysis of mineral properties, comparison with other gems typically worn in jewelry, or from direct observation. No attempt has been made to disparage any particular gemstone, but rather an effort has been made to offer realistic advice on the liabilities and care of gems. The aim is the prevention of loss due to mishandling of more fragile or softer gems. Some gemstones are poor choices for ringstones, but

make

lovely earring or pend-

ant stones.

The information presented book

is

highly condensed.

principles

summary

and terminology

in the text

basic familiarity with the

is

assumed, although a brief

of important concepts

many

presented

is

lowing pages. Further information the

portion of this

A

is

in the fol-

easily obtained

from

excellent specialized books available to inter-

ested readers, as listed in the Bibliography (see page 236). In this edition I have used the new names for Ceylon. Rhodesia, and S.W. Africa: Sri Lanka, Zimbabwe, and Namibia, respectively. However, although Madagascar is

now officially the Malagasy Republic, I have retained the name for simplicity and familiarity.

older

Sins of omission, in preparing a

increase with time.

invariably

The data presented herein were compiled from many sources. The primary sources are standard reference

many

made and

book of

easily criticized.

It

this type, are is

likely that

of the finest stones in existence are not on display

but rather are held in private collections. There are

INTRODUCTION probably a number of mineral species that have been faceted by hobbyists and either never reported in the literature or inadequately referenced. In all

plea

again

is

made for assistance from

work more complete, comprehen-

future editions of this sive

such cases, a

readers in making

At a temperature of absolute zero 273°C), atoms are at rest and do not vibrate. At all temperatures above this, however, atoms are in motion. At high temperatures, atomic vibration is so violent that bonds may form but are immediately broken. This is the situation in (

completely

a gas or vapor, where atoms and molecules

and accurate.

random and occupy

all

At lower temperatures atoms

THE NATURE OF GEMS

fly

about

at

the space available to them.

longer period of time, and

stay

in'

contact for a

may become bonded

together

definite crystalline structure

and compounds. Every mineral is characterized by a and a chemical composi-

freedom of motion. This is the characteristic of liquids, in which atoms slide over each other but remain essentially in contact. Lowered temperatures further slow down atomic vibrations and prevent the atoms from breaking the bonds that form as a

tion that varies within defined limits.

result of electrical attraction.

but

As we have als.

seen,

gems

are, with

few exceptions, miner-

Minerals are naturally occurring chemical elements

The

made

which are the basic of matter. Every chemical element con-

universe

is

of atoms,

chemical units sists of atoms of a type characteristic of that element. Within the atom are yet smaller particles, some of which

have electrical (+ or — charges. The positively charged particles are called protons and are concentrated in the )

center or nucleus of the atom. Negatively charged parti-

surround the nucleus. electrically neutral because the number of positive charges within it is balanced by an

cles, called electrons,

An

isolated

equal

number

atom

is

of negative charges. However,

still

retain a large degree of

If the vibration is slowed down enough, the atoms become locked in fixed positions relative to one another. Every atom in a given mixture of atom types tries to

surround

itself

with specific kinds of other atoms,

and

relative positions.

results in a crystal structure.

atoms may

Crystal structures are both repetitive and symmetri-

One can discern, within a structure, planes of atoms These may be bonded to adjacent

borrow electrons from each other, some atoms thus acquiring a net + charge and some a net - charge. Charged atoms are called ions. Positive ions are known as cations, and negative ions are called anions. An atom that loses an electron seldom gives it up entirely. Usually the loan is half-hearted, and the donor atom shares the electron(s) with the recipient atom. Neither atom will give up the electron(s) completely, and the result is an endless tug-of-war that keeps the atoms

cal.

involved joined together.

surrounding the atoms

some

atoms do gain or lose elecBut the atom losing an electron thus acquires a positive charge, and a neutral atom gaining an electron becomes negatively charged. In

cases, however,

trons entirely and

Since

it is

become

ions.

a basic law of nature that unlike charges attract

each other, the ions are held close to each other in a way similar to the atoms merely sharing electrons. The forces holding atoms together are called bonds. Electron sharing produces covalent bonds, which are usually very strong. The second example mentioned above, involving the attraction of ions, is called an ionic bond. Other types of bonds are generally weaker than these

bond

all at

This becomes a kind of unit of pattern in three dimensions. The pattern is analogous to wallpaper, in which a (perhaps geometric) unit of pattern is repeated at regular intervals. The repetition of molecular pattern units in three dimensions

fixed distances

of a specific type.

planes of atoms of a different type.

If

these bonds hap-

be weak, the plane of bonds may be a zone of structural weakness in the material. On a macroscopic scale, the crystal might tend to split along such planes.

pen

to

Furthermore, acts with the

light traveling

atoms

through the material

in the crystal structure.

The

inter-

interac-

and the electrons Bonds between which electrons are

tion involves the light energy itself

atoms

more in

in the structure.

are, in a sense, regions in

highly concentrated, and therefore

a structure are localized

sets of atoms. in direction.

Bond

in

bond energies

regions between specific

strengths within a crystal vary greatly

Consequently,

ways, depending on the path

light is affected in different it

takes through the crystal.

Crystal properties are directional, because the bonding

within a crystal structure varies with direction, as well as the types of atoms involved. This concept

is

critical in

understanding the properties of gems and minerals.

CRYSTAL STRUCTURES AND PROPERTIES

types.

A group of atoms held together by bonds in such a way form a cohesive unit is called a molecule. The molecule is the smallest amount of a chemical com-

as to

pound

that displays

all

the characteristics of the

compound.

All solids are crystals, and every mineral is characterized by a crystal structure. Different minerals may have structures that are built of similar or even identical pattern

CRYSTAL STRUCTURES

units.

However, no two minerals have exactly the same and chemical composition. glass is rigid but is not considered a true solid

structural pattern

A

because the atoms within range periodic array.

it

are not organized in a long-

A glass may form when, upon cooling

from a molten state, a material solidifies before the atoms can arrange themselves into a pattern. The strong bonds linking the atoms together overcome random motion of the atoms, and the material may become both rigid and hard. There is no single temperature at which all the bonds loosen and allow the atoms to move again. Consequently, glasses have

no specific melting point but rather

soften gradually and eventually begin to flow. Obsidian

and tektites are examples of naturally occurring glasses. Chemical composition and structure both play a role in determining the properties of a mineral or gemstone. For example, consider the minerals halite (NaCl) and cerargyrite (AgCl). Both substances crystallize in the isometric system, form cube-shaped crystals, and are colorless and transparent. The crystal structures are identical: each chlorine atom is surrounded by six metal atoms at equal distances. A plane of atoms in the structure parallel to a cube face would contain rows of alternating chlorine and metal atoms in both minerals.

The

properties of these minerals, however, are very

different.

The

cerargyrite

is

specific gravity of halite

5.55!

The

is

2.17, that of

refractive index of halite

is

1.54,

whereas that of cerargyrite is 2.07. These large differences may be attributed to the presence of silver in cerargyrite as opposed to sodium in halite. In the above instance, the structures and compositions of the minerals discussed are very simple, and the metal atoms are major essential components of the formulas.

A

study of mineral properties reveals, however,

can have a major on physical properties. This applies both to different minerals with slightly different formulas and to variathat even small variations in chemistry

effect

tions in chemistry within a single mineral species.

A

good example of this is the mineral beryl, which is aluminum silicate. Pure beryl is colorless. However, a relatively small amount (less than percent) of chromium, substituting for aluminum in the structure, is sufficient to produce a brilliant, intense green color. The substitution occurs because the ions of aluminum and beryllium

1

chromium

are both trivalent (have a net charge of +3)

and are about the same size. If there is chromium present in the solution from which the beryl crystal grows an occasional chromium atom is incorporated in the structure in the site normally occupied by an aluminum atom. As few as two chromium atoms in 5,000 aluminum sites will produce a green color. Iron in the beryl structure results in yellow or blue coloration, whereas manganese produces a pink color.

Many

minerals

impurities. In

AND PROPERTIES

may have

5

their color thus altered by

most cases the impurity atoms are present

in sufficiently large quantities to also affect physical

properties such as specific gravity and refractive index. In general, impurities

do not affect cleavage or hardness.

Moreover, an impurity atom usually

somewhat

element

replaces.

it

in a crystal structure is

different in size

The

result

is

and charge from the

that the structure can

amount

tolerate the presence of only a limited

of the

impurity before the strain on the structure becomes so great that the crystal cannot

grow

at

all.

Most cases

of

chemical substitution involve amounts of impurities ranging from less than 1 percent to as much as 10 percent. There are, however, numerous examples of minerals in which complete substitution is possible. An example is the mineral siderite (FeCOj), a very common carbonate in ore deposits.

The element manganese may

substi-

amount. If 49 percent of the iron is replaced by manganese, the mineral is termed a highly manganiferous siderite. If the manganese content exceeds the iron content, the mineral is considered a new species: rhodochrosite. Pure rhodochrosite has the formula MnCOi, and we might say that iron can substitute for manganese in any amount in tute for iron in the siderite structure in any

the rhodochrosite structure. Obviously, the structures of

and rhodochrosite are identical. These two mincomprise what is known as a solid solution series. The physical and chemical properties vary continuously from one end member of the series (in this case, pure rhodochrosite or pure siderite) to the other. siderite

erals

many

is said to be you can make a graph showing the variation in a parameter such as refractive index as the composition changes along the series, and the graph will turn out to be a straight line. This type of relationship is very useful, because within such a solution series you can determine the chemical composition just by measuring the refractive index! A graph of specific gravity vs. composition might show a similar relationship. A major problem in using such graphs is the oversimplification of the relationship between properties and chemistry. Usually more than one element may substitute for another in a crystal structure, and one must first sort out the separate effects of each substitution before a simple graph can be used with confidence. Gemologists sometimes have a tendency to overlook

In

linear; that

cases the variation in properties is,

mineralogical literature in evaluating gemstones, especially in cases

following

is

where

solid solutions are involved.

an example of

The

this oversight.

Mineralogical convention states that,

in

the case of a

simple two-component solid solution series, the 50 percent composition marks the dividing line between the

two end-member species. One of these two species may

INTRODUCTION be

much more

familiar than the other.

A good example is

ORIGIN OF GEMSTONES

the case of amblygonite: (Li, Na)Al(PO.,)(F OH). Analy-

shown that complete substitution is possible between fluorine (F) and hydroxyl (OH) in the structure. Chemical analysis for these anions is tedious and beyond the range of the gemologist. However, measurable physical properties are markedly affected by the F-OH substitution. When hydroxyl is present in greater amounts than ses have

we have a new species, called montebrasite. Most gems cut from members of this series are ambly-

fluorine,

many stones have been discussed in the when a glance at the optical data reported for the gem reveals properties belonging to gonite. However,

literature as amblygonite,

montebrasite! Montebrasite

is

not discussed at

all

in

Rocks make up the crust of the Earth. They are the most and their study provides clues about the long and turbulent history of our planet. Rocks are made up of minerals, which are the chemical building blocks of our planet. A rock can consist of one mineral, as in the case of pure limestone, which is composed entirely of the mineral calcite. Most rocks, however, are made up of several minerals. These are usually present in the form of crystals or grains. The history and origin of a rock can be deciphered from its mineral content and the way the mineral grains contact each other. This latter feature, known as texture, is espefamiliar of geological materials

may be the correct species designation for many gems now labeled amblygonite in collections. A much greater awareness of

cially

the variation of physical properties with chemistry

ROCK CLASSIFICATION

standard gemological literature, whereas this

required in gemological work;

is

such as refractive index is very sensitive to small variations in chemical composition. In addition, most minerals have several structural sites (positions), each of which

can accommodate a variety of different atoms. For example, in the mineral diopside (CaMgSi20e), sodium may

amounts! In such cases

it

member of a group of about

eight minerals

with essentially the same structure and differing in com-

The appearance of many of these species is and they have many similar properties. A gemstone can be initially identified as a member of the diopside-hedenbergite series, for example, and then further testing may indicate exactly where the gem in question lies within the series. Other well-known mineral groups, in which this approach is useful, are the garnets, feldspars, spinels, humites, sodalite, and tourmaline. position. similar,

A

members of important groups of gem found on page 241. The group concept of relating similar gem species has been used throughout this book. listing of the

minerals

ture, the size of the mineral grains or crystals present,

and obvious physical features such as lamination or banding. There are three basic types of rocks. Igneous rocks form as a result of the cooling of molten material called magma that usually originates deep in the Earth, below the upper layer called the crust. Magma may have varying composition, and different types of magmas produce different types of igneous rocks. A magma rich in water and silica (Si0 may cool to yield a 2

light-colored rock

known

)

as granite; a silica-deficient

depending on the cooling history, including rate of cooling and pressure changes within the molten material. If magma solidifies deep within the Earth and cools very slowly, crystals have a chance to grow to large size, resulting in a rock with coarse texture. Igneous rocks that cool more quickly, as they would nearer the Earth's surface, develop a fine texture. An extreme example of a fine-textured rock is volcanic glass, which cools so quickly that crystals do not have a chance to develop at all. Two

The above discussion makes it clear that the gemologist should become accustomed to thinking about gems in terms of families or groups of minerals. Diopside, for a

according to their overall chemical

not a simple matter to

is

tional variations.

is

classified

magma may produce a black, dense rock called gabbro. A given magma may produce various types of rocks,

correlate changes in physical properties with composi-

example,

Rocks are

composition, the minerals they contain, the rock tex-

magnesium, and alusame time and in different

substitute for calcium, titanium for for silicon, all at the

in classifying rocks.

much of the needed infor-

mation is readily available in standard mineralogy texts and is reported in this book. It is important to remember that chemical variations in minerals are seldom simple. The geological environments in which minerals form are extremely complex, and a growing crystal often has a wide variety of elements competing for space in its structure. A parameter

minum

important

may contain the same minerals in the same proportions. They are differentiated according to grain size, which is a reflection of their cooling history. different rocks

Igneous rocks formed within the Earth are called and usually have coarse textures.

intrusive or plutonic

Extrusive rocks are formed

when magma is ejected at the

Earth's surface, as in a volcanic eruption, and are fine

grained as a result of rapid cooling. Light-colored igneous rocks are sometimes called acidic,

is

a

misnomer relating to the time when

mineral acids such as

"silicic

it

was believed

that

acid" were responsible for

ROCK CLASSIFICATION rock formation.

The chemical

opposite of an acid

is

a

base, and basic rocks are dark-colored rocks that were

once presumed deficient in "silicic acid." The terms are no longer valid but are mentioned here because they are

metamorphism, and one can determine metamorphism in an area by examining the mineralogy of the rocks over a wide area. Metamorphic

gional or contact

the extent of

rocks are classified according to bulk chemistry, reflecting

the literature.

the composition of the original, unaltered rock and the

Sedimentary rocks are so named because they are of sediments, which are either rock and mineral fragments or the mineral and chemical weathering

metamorphic minerals present, which indicate the temperature and pressure reached during metamorphism. The Earth is in a constant state of change. Rocks in some places are being melted or pulled into the interior;

occasionally used

in

composed

products of these materials. About 75 percent of the rocks exposed at the Earth's surface are sedimentary,

and they form by the deposition, in water or air, of rock and mineral particles or by the precipitation of mineral material in water. The most obvious and distinctive feature of sedimentary rocks is banding, or layering, known as stratification. Mechanical or detrital sediments include sand, gravel, clay, silt, and mud. These particles may become rock through the processes of cementation or compaction. The first step in the hardening process is consolidation, accompanied by the expulsion of water and volatile materials, and the entire process may be referred to as lithification. An evaporite is a sedimentary rock formed by the evaporation of saline water (either an ocean or lake) with the consequent precipitation of salts, such as halite, gypsum, and borates. Coal is a sedimentary rock composed of the remains of plants that lived millions of years ago. Chemical sedimentary rocks are formed by accumulation of marine precipitates, usually calcium carbonate. The most familiar rock formed in this

way

is

limestone. Solutions containing

magnesium

may later alter a limestone

bed, producing a massive bed

of the mineral dolomite.

Some sedimentary rocks are down by winds

created by consolidation of particles laid

or even glaciers.

others are being created in spectacular volcanic episodes. Sediments are being deposited and

compacted

in

oceans throughout the world. The earth is a closed system, with nothing added or removed (noting the negligible addition of meteoritic material). (The chemical elements of the Earth are thus repeatedly mixed and separated by geologic processes.

The

entire process of

rock genesis, destruction, and alteration comprises a

Sedimentary rocks are formed as a result of the of other rocks. Igneous rocks are created by the cooling of magma and hot solutions. Metamorphic rocks result from the transformation of igneous and sedimentary rocks by heat and pressure. All these rocks, in their turn, are worn down and become new sediments. cycle.

breakdown

The

so-called geologic cycle

plex

mechanism

of creation

is thus revealed as a comand destruction of rocks.

Geologic structures may be characteristic of certain rock types. For example, a volcano

is

clearly

composed

of igneous material. Large folds visible in rocks exposed

on a mountain slope are evidence of the action of metamorphic forces. Terraced cliffs, such as those exposed in the Grand Canyon of Arizona, are bedded sedimentary rock layers. It

is

important to remember that gems are simply

Metamorphic rocks are created when Earth pressures and heat alter previously existing rocks. Metamorphism is a word derived from the Greek, meaning "change of form." Any kind of rock may be metamorphosed, and

minerals, albeit of a very special quality. Minerals are

a reorganization of the mineral and

ent structural arrangements, depending on external param-

the major result

is

chemical components of the previous rock. Some minerals that form in a given set of geological conditions are unstable in drastically different conditions. In the latter

down, decompose, and recrystallize into other minerals that are more stable in the new conditions. Rocks can be metamorphosed on a wide scale as a result of the kinds of forces that produce mountain ranges. These are known as regionally metamorphosed rocks. Alternatively, a rock bed, such as a limestone, may be invaded by magma forced up from deep within the Earth. The heat and chemical components of the magma chemically and physically alter the limestone, resulting in the formation of a wide range of new minerals. This process is called contact metamor-

eventuality they actually break

phism. Certain minerals are very characteristic of either re-

components of rocks. Every mineral species is characterized by a definite structure and chemical composition. The same chemical ingredients may crystallize in differsuch as temperature and pressure. Although they may have the same composition, these different structural arrangements qualify as distinct mineral species, such as, for example, rutile, anatase and brookite. which eters,

are

all

composed

of titanium oxide.

The

conditions at

the time of mineral formation determine which of the three mineral species with this composition will form.

The

controlling influence of physical conditions

is

metamorphic rocks. During metamorphism the temperature and pressure conditions in a

most clearly seen region

may

in

rise greatly

over a period of time.

A

given

assemblage of chemical ingredients may be stable in the form of a certain mineral at low pressure and temperature but when these conditions change beyond a certain point, that mineral may no longer be stable. The mineral

,

INTRODUCTION

8

then decomposes, and the chemical constituents range themselves

new

in a

way

that

is

more

ar-

stable in the

conditions.

in a large

body of

basalt that

olivine crystals of large size

A good example of this is the mineral quartz, the most common mineral on Earth. Quartz, in the form we see as component of beach sand, is stable temperature of 870°C. Above this temperature

pretty crystals or as a

up

to a

the

framework of Si and

O atoms characteristic of quartz

vibrates too rapidly to hold together in the pattern of the

quartz structure.

An

inversion, or

change

in structural

at the

bottom. In

fact,

Gemstone occurrences

Gems are

complex.

movement

of the

atoms

higher temperatures. However, even this structure

at

are usually

grow free of imperfections, and fractures.

The environment same

the

of formation of a

way

torn

chance has acted

new

larger or of better color than

known

as cristobalite, forms.

The

cristobalite

capable of handling very large atomic vibrations, but only up to a temperature of 1710°C. At this temperature no structure of Si and O atoms is stable, and is

cristobalite melts to a very viscous liquid.

The atoms

in

the melt are then free of the relatively rigid atomic bonds that hold a crystal structure together

much

as

is

and can vibrate as

necessitated by higher temperatures within

the melt.

A

given rock, with a particular history of formation,

therefore characterizes a very specific range of condi-

which minerals can form. The environment of is thus a combination of specific conditions, such as temperature and pressure, available chemical components, and such miscellaneous factors as solution flow, metamorphic directional stresses, and rates of cooling and heating. The chemical environment is determined by local rock types and their mineral tions in

formation of a mineral

gem

as for any other crystal of the

is

mineral,

somewhat more

very special mineral oddities in that

apart by atomic vibration at 1470°C, and a totally structure

be found

tions that allowed crystals to

GEM SCARCITY

date the increased vibrational

likely

they are very pure or have formed under special condi-

(Si0

)

would most

we do find zones of coarse-grained

sive bodies.

inclusions, cavities,

2

flow,

olivine at the lower part of lava flows or large intru-

arrangement, occurs and we have a new mineral called tridymite. Tridymite has the same composition as quartz but a different structure that is stable at higher temperatures than the quartz structure. The tridymite structure, in fact, is more open, allowing it to accommo-

formed as a thick lava

or within an intrusive dark-colored igneous rock mass,

in a

the species. In this sense, cal freaks.

They

that

crystal

same

may be

species, but

produces crystals that are usually encountered in

is

gems

are actually mineralogi-

are not abundant and are restricted in

occurrence only to those localities where conditions were suitable for their formation. If the mineral in question

is

rarer.

rare,

A

gem-quality crystals of that species are

much

particular mineral species, such as topaz, for

example, may be widespread and abundant throughout the world. However, large transparent crystals of a deep pink or orange color are exceedingly uncommon. Pink and orange gem topaz, seen in a geological context, are so rare that it is amazing they have been found at all! Rarity in gems is thus a function of several factors. In some cases the various requirements of composition and

conditions of formation of a species are seldom fulfilled simultaneously, as in the case of proustite and mangano-

known

Such species are therefore rare in their own whether they form crystals transparent enough to cut. Sometimes a mineral species is not rare, but transparent, cuttable crystals are very seldom encountered. This is the situation for most of the so-called collector gems. Another case is rarity of color. A good example is emerald, the deep green variety of the mineral beryl.

as paragenesis, can be reduced to a simple rule: Minerals

Beryl occurs throughout the world, usually in pegmatites

are found where they ought to be. This seemingly simple

(see

content, plus the introduction of materials by migrating

waters or vapors. Obviously, the formation of a mineral plex

affair.

is

often a

mineral environment and formation, collectively

statement

com-

Conceptually, however, the whole subject of

is

really the first rule of mineral exploration.

tantalite.

right, regardless of

page 53). Emerald owes its green color to the element chromium. Chromium, however, is not usually pres-

For example if you want to locate a source of peridot you must first know that peridot is the gem form of the

ent in pegmatites.

mineral olivine. Olivine

found

,

A

basaltic

magma

is

characteristic of basaltic rocks.

has the right chemical ingredients for

in

its

Its

geochemical environment

dark-colored (basic) igneous rocks. Beryl in

is

is

rather rarely

these latter geologic environments, largely because

primary constituent, beryllium,

is

rare in basic rocks.

the crystallization of olivine and also exists at the right

The conditions necessary for the occurrence of emerald,

temperature. Olivine

that

is,

in fact, the

highest melting point in a basaltic is

the

first

to crystallize

when

mineral with the

magma, and

the

magma

therefore

cools.

The

appear within the melt are heavier than the surrounding liquid and consequently sink. Thus,

olivine crystals that

is,

the formation of beryl plus the availability of

chromium, are mutually incompatible! This accounts for the worldwide paucity of emerald. The reasons become obvious when one understands the geologic factors. Finally, there

is

scarcity in size. Topaz, for example.

ROCK TYPES occurs

in crystals that

ROCK TYPES

weigh hundreds of pounds. These

are usually colorless or very pale yellow or blue.

How-

Igneous Rocks

ever, topaz crystals of a fine pink color are never seen in

sizes larger than a

white topaz

topaz

is

A

few inches.

huge faceted gem of

not especially rare, but a 10 carat pink

is

INTRUSIVE

very rare indeed.

Likewise, rubies of very fine quality (color and trans-

Granite — core of

composed

many mountain

ranges. Coarse tex-

of potassium feldspar, quartz, plus

parency) are extremely rare over about 10 carats, but

ture,

sapphires, which are mineralogically equivalent to ruby

mica or hornblende and accessory minerals.

(both are the mineral corundum), are encountered in

Syenite

hundreds of carats. Large amethyst crystals are found in many localities. However, pieces free of inclusions weighing more than 50 carats are quite rare. In general, rarity is a combination of a number of factors, all of which depend on the basic geology of a gem species plus the status of the

fine grained.

crystals weighing

marketplace. Scarcity

is

a function of the following factors:

geologic abundance of the species color, size, availability

demands

of the market.

gemstone occurrence

geologic feature.

manufactured will

in

is

human

it

cannot be replenished

lifetimes. Synthetics

can be

the laboratory, but the value of natural

not be affected as long as they can be distin-

guished as rare natural objects of great beauty.

The gem market is continually faced with the threat known gem deposits or loss of production

of depletion of

due

to political factors. This puts great pressure

known sources

to

demand

Their main functions have been to hide, concentrate, transfer, store, and display wealth. Gems are what might be called "real value" commodities, with desirability in all cultures', throughout all the periods of cial products.

exotic elements.

Diorite

Geological scarcity accounts for such rare gems as

and taaffeite. Only one painite crystal has been found, and less than one hundred cut taaffeites are know. To be sure, more specimens of both materials may exist; painite resembles ruby and taaffeite looks like mauve lections

and

may

exist in various col-

inventories. Nonetheless, such rare collec-

gems offer a situation comparable to art. Rembrandt is dead, and no additional original Rembrandts can be produced. By analogy, an exhausted gem deposit can produce no more gemstones. tor

this in

mind, consider the future of

We may someday

parable to the levels of great

art.

command

gem

tle

Home

of

like

rare,

quartz,

some

lit-

biotite.

Granodiorite— like

diorite, but richer in

potassium feldspar.

— like diorite, but contains some quartz. Monzonite — intermediate between syenite and diorite.

Tonalite

Gabbro— diorite rich

in calcic plagioclase feldspar; conpyroxenes as opposed to amphiboles. Anorthosite — rock composed almost entirely of anor-

thite feldspar.

Diabase — fine-grained gabbro typical of small intrusive bodies.

— dark rock composed of pyroxene and olivine. Dunite — peridotite-like rock containing chiefly olivine. Kimberlite — an altered peridotite characterized by highPeridotite

pressure minerals.

EXTRUSIVE Rhyolite

da Vinci "Last Supper," but there is (at of this writing) also only one painite.

— light-colored, fine-grained rock, with compo-

sition like granite.

Obsidian — volcanic

glass,

with overall composition

like

rhyolite.

Pumice — "frothy" volcanic rock,

full

of gas bubbles,

and

on water!

Porphyry — igneous rock with different grain

sizes, reflecting

cooling history; larger crystals called phenocrysts fine-grained groundmass.

lie in

The phenocrysts formed by

slow cooling, and then the rock was suddenly chilled. Basalt

— dark-colored, fine-grained

flows.

Very widespread. Also known as trap rock.

Scoria

— porous,

rock, typical of lava

cinderlike rock seen at tops of lava

flows.

Andesite — volcanic equivalent of diorite, dark colored. Trachyte — volcanic equivalent of syenite.

prices.

comThere may be only one

see rare stones

immense crystals and many gem minerals.

— dark colored, contains plagioclase feldspar,

will float

painite

With

Pegmatite — very coarse-grained rock, composition granite. Frequently contains

history.

spinel; misidentified cut stones

or no quartz;

creates rising prices.

Gems have had great appeal throughout history as finan-

human

little

on other

meet world demand. Depletion of

supply coupled with high

contains

tains

a very rare and transient

Once exhausted,

within the span of

gems

question; desirable

and freedom from imperfections; market (number of producing localities and the sizes

of the deposits);

A

in

— similar to granite;

some

prices

least, at the

time

Sedimentary Rocks Conglomerate — made of large, rounded pebbles and smaller grains, cemented together.

INTRODUCTION

10

Sandstone — composed of sand-size (between 1/16 and 2 mm particles. Sandstone refers to particle size, not composition; therefore, quartz sandstone is made of quartz )

grains.

Arkose — sandstone composed chiefly of feldspar and

metamorphism. Does not show tendency

Marble — coarse-grained calcareous rock produced by metamorphic recrystallization of limestone. Quartzite — dense, compact rock, produced by recrys-

quartz grains.

tallization of quartz grains in a

Gray wacke — dense, dark-colored sandstone with rock fragments and clay particles.

sandstone.

Shale — fine-grained rock composed of clay or

silt-sized

(microscopic) particles.

Limestone — chemical precipitate of calcium carbonate in sea water. Sometimes the fossil remains of large reefs, built by corals and other animals long ago. Chalk — calcareous chemical precipitate, composed of tiny marine plants and animal skeletons, plus biochemically

to split along

planes, but minerals are arranged in parallel layers.

sedimentary quartzite or

Skarn — complex mineral assemblage produced by contact metamorphism of an impure limestone or dolomite. Minerals of economic value in such assemblages are often called contact deposits.

IDENTIFICATION

OF GEMSTONES

deposited calcite.

Dolomite — massive sedimentary rock composed chiefly

There are approximately

of the mineral dolomite.

eral species.

Travertine

— limestone formed in caves by slow evapora-

thirty-five hundred known minfew new minerals are added every year, and occasionally an existing species is discredited when

A

careful analysis reveals

tion of solutions.

als.

The number

Concretions are masses of cementing material, the same cement (such as silica or iron oxide) that caused lithification

sometimes assume fantastic and grotesque shapes. Nodules are masses of mineral material differing in composition from the rocks in which they are found. Geodes are hollow, more or less round objects, often containing an interior lining of terminated crystals. Geodes are usually made of quartz, but may contain a wide variety of other minerals. Geodes commonly occur in shales, but also form in gas pockets in igneous rocks and accumulate in the soils resulting from the weathering of of nearby sediments. Usually spherical, they

such rocks.

to

be a mixture of other mineris

very small in

huge list of compounds known to chemistry. This is because minerals are naturally occurring chemical elements and compounds. There are geochemical restrictions that limit the number of possible mineral species, namely, the tendency for certain elements to be restricted to specific geochemical environments. Random chance also plays a major role in terms of the temperature and pressure that happen to be prevalent in the environment where chemical reactions occur and minerals are forming. Very rarely is a new mineral species found in large, well-formed crystals. An example of such an occurrence is the mineral brazilianite, which was described on the basis of spectacular, large, and even gemmy crystals

comparison

SEDIMENTARY FEATURES

it

of mineral species

to the

discovered in Brazil. Usually, however, a

recognized only with great

may be

difficulty.

An

new mineral

is

astute observer

studying a complex mineral assemblage and

recognize a few grains of an unfamiliar mineral. Detailed

Metamorphic Rocks

analysis

may show

that the material has a chemical

com-

position slightly different from another, well-known speSlate

— formed by the low-grade metamorphism of shale.

Pressure causes aligning of the clay particles in the shale, resulting in easy breakage of the rock into layers. Phyllite

May

— next step upward in metamorphism from slate.

have a shiny appearance on broken surfaces, due to

cies; the difference

unknown

may be

large

enough

to warrant

new species. In some cases there is barely enough of the new mineral even to perform a complete chemical analysis! Most of the new minerals added to the known list are in this category of calling the

material a

recrystallization; tends to break between layers to produce characteristic uneven, wavy surface. Schists are

obscure grains very limited in quantity. Very sophisticated analytical devices are required for this type of descriptive work. The situation with gems is not so demanding. Usually

named according

the gemologist's major problem

parallel alignment of recrystallized mineral grains.

Schist— can be derived from various rock types by intense

to the minerals they contain. Often

is

to pin

down

the

com-

characterized by folded, crumpled look.

position of a gemstone in order to locate the material

Gneiss— coarse-grained, banded rock formed by intense

within a solid solution series, as for example in the case

1

GEMSTONES

IDENTIFICATION OF of garnets and feldspars. In

some such cases

a measura-

such as refractive index, may vary linearly with chemical composition. The composition may therefore be determined by carefully measuring refractive ble property,

index and using a graph to pick off the corresponding chemistry. This type of analysis works only in simple

where the only major of iron and magnesium. In

1

complex for elaboration here. A brief summary of the approach is, however, warranted. X-rays are pulses of energy, like light and heat, but with very short wavelengths. The level of energy in an X-ray beam is on the same order of magnitude as the energy associated with the electrons that spin about the nucleus of

beam

all

types of

cases, such as in the olivine series,

atoms. Consequently,

chemical variable is the ratio most solid solution series, however, the chemistry is far too complex for simple correlations, and a combination

with a standard refractometer; the microscope can some-

can interact with the electrons of the atoms in the crystal structure. The more electrons an atom has (that is, the heavier the atom) the greater the degree of interaction. The incoming X-ray beam enters the crystal in one specific direction. However, the electrons in the crystal's atoms absorb the X-ray energy, and re-emit this energy almost instantaneously in all directions (radially). The situation is as if each electron were itself acting as a source of X-rays. All the electrons affected within a particular atom combine their radiations and the atom itself acts as an X-ray source. Intuitively, one would expect that the X-rays emerging from the crystal would be in the form of a glow or diffuse spherical emanation of uniform intensity. However, the atoms in the crystal are arranged in rows and layers, with definite spacings between them. The spacings in a crystal structure are about the same size as the wavelength of the X-rays. This situation is analogous to an optical

times be used for direct measurement of refractive index,

device

using a technique discussed in standard gemological texts

which may be found

of tests

is

needed

The most tion

is

fitted

for identification.

useful instrument for

gemstone

identifica-

the microscope, especially a stereoscopic type

with special darkfield illumination

in

which

light

enters the gemstone only from the sides. This instrument is

ideal for the

examination of inclusions, which are

frequently diagnostic in identification. Magnification also reveals cleavage developed

on a small scale

as well as the

degree of surface finish on a stone, which allows an estimate of hardness. Fracture

may

also be

determined

by observing small chips on the girdle of a faceted gem. The refractometer is used to measure, with good accuracy, the refractive index and birefringence of most

gems.

Some gems have indices too high for measurement

(see Bibliography

on page

236). Specific gravity

may be

determined with heavy liquids or with torsion balances. Gravity measurement plus refractive index usually allows for

unambiguous

identification of a gemstone. In

some

cases the spectroscope provides very rapid and unamin distinguishing between almandine garnet and ruby. The polariscope is useful in determining the optical character of a gemstone. There are only about two hundred fifty mineral species that have been cut as gems, a fact that makes the

biguous analysis, as for example

gemologist's

life

easier than that of the mineralogist,

who

is concerned with more than three thousand five hundred species. It is important to remember, however, that at any time a mineral species may be encountered in a form with gem potential. If such a material is brought to

a gemologist for identification, he or she fied

when

the properties of the substance

may be

mysti-

do not match

anything in standard gemological reference tables. In such cases it is necessary to resort to more powerful techniques for identification. An extremely powerful diagnostic tool, routinely used

When

known

an X-ray

if

in

from a row of regularly spaced point sources is reinforced along certain directions and is completely cancelled out along other directions! These directions can be predicted and described mathematically, based on the wavelength of the radiation and the spacing between the point sources.

The case

complex because the

detailed principles of X-ray

methods are too

is

much more

directions (dimensions) simultaneously, and the exact

beams

is

result of all this

is

interaction of the various to calculate.

The

enormously difficult whereas a single

that

beam enters the crystal, a divergent array of diffracted beams comes out. These diffracted beams come out in X-ray

each beam is the result and a variety of types of atoms, each type contributing radiation based on its particular electronic makeup. The intensities of all specific directions. In addition,

of interactions with various rows of atoms

beams therefore vary widely. camera has been devised in which a

the diffracted

A

special

photographic film.

crystal

surrounded by special The film records the positions and

being irradiated with X-rays

intensities.

The

of crystals

diffraction takes place in three

identification of a mineral in a period of a few hours.

virtually

any standard physics textbook.

diffraction occurs off a grating, radiation emitted

diffracted X-ray beams.

is

it

as a diffraction grating, the principles of

unknown to the gemological fraternity. This is the X-ray powder diffraction camera, a device that can, in most instances, provide unambiguous by the mineralogist,

enters a crystal,

is

(through degree of darkening) the intensities of the These parameters are measured

on the

and listed as a set of line spacings and Such parameters have been measured and

film

tabulated for

all

the

known mineral

species.

A

rapid

INTRODUCTION

12

search of the tabulation usually allows the crystal to be quickly and unambiguously identified

in a

matter of a

few minutes. A major advantage of the X-ray approach

powder

analysis requires a very small

amount

is

that

of sample.

In the case of a faceted gem, a tiny bit of material can be scraped from the girdle with a diamond stylus without

damaging the stone. X-ray methods can be used advantageously in cases where optical and other data acquired by normal means materially

are ambiguous. In

some cases

a

gem

example of a mineral not usually found this instance the

is

a very rare cut

in

gem quality.

In

standard gemological measurements

are not present in tabulations in textbooks, and the

mineralogical literature must be consulted. In another

may encounter a synthetic gem matesuch as a rare-earth garnet, the properties of which

case, a gemologist rial,

are also not tabulated in the sis

would be

definitive here

gem

literature. X-ray analy-

because the tabulation of

X-ray measurements extends to the entire range of organic and inorganic compounds as well as minerals. X-ray equipment is expensive and requires great care in use. The X-ray beams produced for mineral analysis are extremely potent and capable of great damage to human tissue. Many large cities do have complete analytical laboratories that ice.

The

may

offer diffraction as a serv-

active gemologist should

make an effort to when diffraction

locate such a laboratory for those times

offers special advantages in identification.

The gemologist should always remember that the chemcomposition of minerals varies widely, with corresponding variation in physical properties. There is almost always a range of values in parameters such as refractive index, specific gravity and optical spectrum (presence or ical

absence of diagnostic lines). By maintaining a continual awareness of the principles of crystal chemistry, the gemologist can avoid confusion and increase by many times the power of his or her analytical

abilities.

,

Sources

of

Data Used

FORMULA

in

Text

after a plus (+) sign following the

formula are those most

often noted as substituting for elements in the formula.

The chemical composition aspect of

its

of a mineral

definition as a species.

to a periodic table of the

a primary

CRYSTALLOGRAPHY

chemical elements (page 243)

for standard abbreviations of the

Many

is

The reader is referred

names

of elements.

The reader

formulas contain parentheses within which are

listed several

elements, for example (Fe,Mg). This indi-

cates that there

is

a specific position in the crystal struc-

nology.

may be occupied by either iron, or magnesium, or both. The element listed first within the parentheses is some cases

amount on the

structural

site.

determines the species! For example, amblygonite is (Li,Na)Al(P0 4 )(F,OH). However, if the formula reads (Li,Na)Al(P0 4 )(OH,F), we have a new speIn

is

which hydroxyl exceeds fluorine, and the species called montebrasite. Furthermore, if the formula (Na,Li)Al(P04>(OH,F), sodium exceeds lithium and is

degree of complexity associated

with solid solution can be very great.

Any substitution of may (or

elements on a crystallographic structural site may not) have an effect on physical properties.

A good example is BeiALSi 6 0i8, but often containing such elements as Fe, Mn, Cr, V, and Cs. These elements are usually present in such small quantities that they are not written into the formula. However, the mineralogist understands that Cr, for example, which makes beryl the rich green Impurities also affect properties.

beryl,

color

we know

structure. tions

A

suffice here to say that crystals

grow

in

,

classed as yet another species, natromonte-

brasite. Obviously, the

It will

gorized.

now

the mineral

on mineralogy

metry of various types that can be described and cateWhen this is done, it is discovered that all known crystals can be organized according to six major crystal systems: isometric, tetragonal, hexagonal, orthorhombic monoclinic and triclinic. A subclass of the hexagonal system that is sometimes (though erroneously) regarded as a seventh crystal system is known as trigonal. Each crystal system is defined in terms of crystal axes, which are imaginary lines in space that intersect at a common point and whose lengths may be described as equal or unequal to each other. The systems are further described in terms of the angles that these axes make with each other. Various descriptive terms may be used in describing the crystals exhibited by various mineral species. These

this

cies in is

referred to standard books

such a way that their component atoms and molecules are locked together in periodic arrays, much like threedimensional wallpaper patterns. These arrays have sym-

ture that

the one present in greater

is

or crystallography for detailed background and termi-

terms include prismatic (elongated), bladed, acicular (needlelike), filiform (hairlike), equant (roughly equal-

as emerald, substitutes for Al in the

length sides), pyramidal (looking like single or double

detailed knowledge of chemical substitu-

pyramids), and tabular. Sometimes terms are used that

and color changes

in crystals requires a

much

refer to specific

forms characteristic of specific crystal

greater sophistication in crystal chemical principles than

systems (octahedron, pyritohedron, and so forth). Other

can be expounded here. Formulas given in this book are based on the most recent mineralogical studies. Chemical elements listed

state of aggregation: massive (solid

terms used to describe a mineral's appearance refer to and chunky), compact (solid and dense), cleavable (crystalline masses that

13

SOURCES OF DATA USED

14

IN

TEXT

can be cleaved), granular (masses of compact grains), stalactitic (resembling the form of stalactites), oolitic (masses of spherical grains), earthy (masses of densely packed powder). The appearance of a mineral is largely a function of the growth process and the environment of formation. Minerals deposited in sedimentary environments tend to be earthy, stalactitic, oolitic, and sometimes massive. Igneous minerals tend to be crystalline or massive, sometimes cleavable. All these terms are somewhat subjective but are useful in getting a mental image of the appearance of a mineral as it occurs in the Earth.

competent gemologist's working library. It is vital that the field of gemology start moving toward color designa-

CIELAB,

tions (CIE,

use

in daily

in all

Munsell,

OSA-UCS,

etc.) that are

other color measurement

fields.

LUSTER Luster

is

considered a basic descriptive parameter for

minerals but varies somewhat even within a single crystal,

and

its

usefulness

is

therefore limited. Lusters include:

vitreous (the luster of glass— characteristic of most

gem

minerals); pearly (iridescent, pearl-like); resinous (luster of resin); greasy (appears covered by

COLOR

diamond);

The

color of a mineral or gemstone

is

attributes used for identification, but

one of the ful

oil layer);

least diagnostic

of cases).

The

one of the primary it is,

unfortunately,

and useful (except

colors reported include

all

in a

hand-

those men-

Luster

silky (fibrous reflection of silk); dull.

is

a

phenomenon

of reflected light

ple,

gypsum may have

faces; the luster

is

a vitreous luster on

occurs

example

gem quality in

A a

mineral may, at any time, be

new or unfamiliar color.

A good

found in Africa in a striking blue variety in the 1960s and given the trade name tanzanite. The streak (color of a mineral powder) is listed where it is useful for identification. This characteristic applies almost exclusively to opaque, metallic minerals, because the

is

zoisite,

in

some

exam-

crystal

pearly on surfaces parallel to the

These are useful to gemologists primarily as a guide as to what could be expected in the future, that is, the potential in

mostly

is

to the state of aggregation of the mineral. For

excellent cleavage of this mineral; and

color of a gemstone.

and

due

tioned in the mineralogical or gemological literature.

found

adamanfrom a

tine (hard, steely brilliance like the reflection

if

the mineral

aggregates of long fibers (satin spar),

it

has a

can hardly be a useful diagnostic property in identifying gypsum under these circumstances! Luster is primarily divided into two types: metallic and nonmetallic There are also intermediate types, called submetallic. Any mineral that does not have a metallic appearance is described as nonmetallic, and the above descriptive terms are applied. silky luster. Luster

.

powder of most transparent minerals is colorless (white).

The color names applied to gems and minerals have become familiar through long usage. Some gem color

HARDNESS

ards and procedures for measurement have been estab-

Hardness is the resistance to scratching of a smooth Hardness has little use to the gemologist, since gems are not normally scratched as a part of gem testing. A hardness is sometimes taken on the back of a statue, as for example to differentiate between jade and serpentine. But even using the girdle of a gem to perform a hardness test results in chipping on occasion. Hardness depends on the bonding that holds the atoms

lished by international professional societies in the color

together within a crystal structure. This bonding

names, such as "pigeon's-blood" (ruby) or "padparadscharf (sapphire), are vague, but have remained in the marketplace because no useful alternatives existed. However, accurate color measurement instrumentation

is

now avail-

about to revolutionize the gemstone industry. Color specification systems for most colored materials (paints, dyes, etc.) have long been employed, and standable and

is

surface.

is

reflected

A

gemstone colorimeter was used to measure a gemstone color varieties and species for this book. The chapter on color measurement represents the first appearance in the gemological literature of objective gemstone color data, reported in terms considered standard by the color measurement and standardi-

in the ease with which the layers of atoms at a surface can

large array of

be separated, by applying pressure with a sample of another material. If the second material is harder than the first, it will leave a furrow, or scratch, which represents the breaking of millions of atomic bonds on a

zation field.

cally, its "scratchability,"

field.

The future

of

gemology

clearly lies in the direction of

measurement and terminology. Reference books on color technology should rapidly start to appear on the shelves of any

greater objectivity and standardization in

microscopic scale. The hardness of a mineral is, specifiand all minerals can be ranked in order of which one will scratch which other ones.

Mohs established a reference common minerals, ranked in order of increas-

Mineralogist Friedrich scale of ten

ing hardness, as follows:

DENSITY 1.

Talc

5.

Apatite

8.

Topaz

2.

Gypsum

6.

Feldspar

9.

3.

Calcite

7.

Quartz

Corundum Diamond

4.

Fluorite

10.

may be both hard and brittle, as in the case Diamond will scratch any other known material, but a strong hammer blow can shatter a diamond into thousands of pieces. The perfect cleavage of mineral

of diamond.

diamond,

in fact,

allows

Cleavage may be an

it

initial

to be more expeditiously cut. diamond cutting operation, as

opposed to the long and tedious process of sawing. Hardness in a gemstone will determine the degree to which it will show wear. An opal, for example, which is quite soft for a ringstone, rapidly becomes covered with fine scratches in daily use, and the polish is quickly lost. A ruby, on the other hand, will remain bright and lustrous for years, because the material is harder than most of the abrasive particles in the atmosphere that contrib-

gem wear. The hardness

ute to

may

that looks like a scratch

is

actually a

by the supposedly harder material!

vary slightly with

trail

It is

cases the hardness range reported

of

powder

left

is

very small (one unit).

DENSITY is a bulk property of a mateindependent of direction and is uniform within a mass of material under ideal circumstances.

Density, or specific gravity, is

In actuality, the density of a mineral varies widely,

even within a single crystal, due to the presence of impurities,

in

cracks, and bubbles. Density

gem

identification, so the

is

a useful parameter

problems

in its

determina-

tion should be well understood.

Specific gravity

water

at

is

the ratio expressing the weight of a

compared

to that of an equal volume of 4°C. Thus, a specific gravity of 3 means that, at

given material

density of a

compound

a function of several

is

chemical composition and crystal structure. For example, consider diamond and graphite, both of which are crystalline forms of the element carbon.

Diamond has

a density of 3.5 because the carbon

atoms

are tightly packed together in the structure; graphite,

much more

with a

only

loose,

open

structure, has a density of

2.2.

The density of minerals within a solid solution series may vary linearly with change in composition. The effect of chemical substitution

is

seen dramatically

in

the case

of the orthorhombic carbonate minerals aragonite and cerussite. Aragonite

is

CaCOj and same

of 2.95; cerussite, with the of

PbCOi and

shows the liquids.

If

to have a specific density value.

or remain suspended

one place within the

Very accurate measurements

as the liquid.

made by changing

the density

of liquid through temperature variations and

suspending density standards

An

liquid.

denser than the liquid, and if it it remains at one level it has the

of specific gravity can be

column

in

An

sink,

it is

less dense. If

same density of a

may

material dropped into the liquid

the material sinks, it is

measured with heavy

prepared, such as a mixture of bromo-

is

form and toluene, float,

composed

is

role of lead versus calcium in the structure.

A liquid

unknown

has a specific gravity

structure,

has a specific gravity of 6.55! This clearly

Specific gravities are usually

really not critical

whether the hardness of a mineral is 5 or 5 1/2. Fractional hardnesses are reported where the literature has indicated an intermediate value. A range in hardness is much more meaningful, and the values reported in this book represent all values encountered in the literature. In only one case (kyanite) does the hardness of a mineral vary very widely even within a single crystal. In most

that

The

floats

of a material

composition and also with state of aggregation. The measurement of hardness is very tricky and often a mark

rial

4°C, one cubic centimeter of the material in question weighs 3 times as much as one cubic centimeter of water. factors, including

In reality, diamond is very much harder than corundum, even though the scale says they are only one division apart. The Mohs scale is approximately linear from 1 through 9; the curve climbs sharply upward at corundum, however.

A

15

alternative

method

of

in the

column.

measurement

so-called torsion balances, such as the

is

the use of

Hanneman

bal-

ance and the Berman balance used by mineralogists. These devices are designed to weigh a sample first in air and then suspended in a liquid, such as water or toluene. The weights in both media can be measured quite accurately and specific gravities can sometimes be reported to two decimal places. A major problem in all density measurements is the presence of impurities within the crystal being studied. These impurities hardly ever have the same specific gravity as the host material, and their presence results in measurements that are of limited use for identification purposes. Surface tension

may

also "float" a mineral

and a torsion balance, resulting an erroneously low specific gravity measurement. Accu-

grain in both heavy liquids in

measurement involves absolute cleanliness, specimen preparation, accurate temperature control, and replicate measurements. The specific gravity measurements reported in this book represent values taken from both the mineralogical and gemological literature. In most cases a range is rate density

great care in

reported, as well as a typical value or (where reported) the value of the pure material.

SOURCES OF DATA USED

16

IN

TEXT

CLEAVAGE

sensitive to

minute changes

composition and

in

strain in

the crystal structure.

Hardness, as discussed

earlier,

is

the scratchability of a

and the related property, fracture, are both manifestations of the tendency of certain crystals to

material. Cleavage

break along definite plane surfaces. As hardness, the underlying principle

bond

strengths.

If

is

in the

case of

that of relative

there are planes in a crystal structure

along which the atomic bonds are relatively weak, the crystal

may tend

to break along

such planes. Under ideal

circumstances, a cleavage plane might be smooth and flat, virtually

on an atomic

cal;

within a crystal

is

symmetri-

consequently, the planes of specific bonds are sym-

metrically disposed within the crystal. Cleavage planes are therefore as symmetrical as crystal faces.

By the

can have no cleavage whatever. is rather a supercooled liquid, in which the atoms are not arranged in a long-range periodic array. There can therefore be no uniform bond layers and hence no cleavage. Cleavage is usually described with reference to crystallographic axes and directions. However, this nomenclature is beyond the scope of this book, so in all cases

same reasoning, Glass

is

glass

not crystalline but

only the

number

of cleavage directions in a

gem

has been indicated and whether the cleavage (eminent), good,

fair,

is

species perfect

or poor. Sometimes there are

dif-

ferent degrees of cleavage perfection in different directions within the

same

crystal,

and these have been so

The term parting refers

to breakage of minerals along

directions of structural weakness. Unlike the situation in is

not present in

all

specimens of a

given species.

Fracture

is

the

way a mineral breaks other than along

The

descriptive terms for this prop-

erty are: conchoidal (shell-like, distinguished by concen-

curved

lines; this

is

the

way

glass breaks); fibrous;

splintery; hackly (consisting of sharp-edged

and jagged

fracture surfaces); uneven.

Gems with worn

all

directions perpendicular to the light path.

light passes

from one medium (such as air) into light is actually slowed down.

another (such as water) the In addition, the light path

is

bent.

The deviation

is

always

referred to a line perpendicular to the interface between

which is known as the normal to the The light is always bent toward the normal in the medium in which the light travels slower. The ratio between the velocity of light in the two the two media, interface.

media the

is

first

called the index of refraction or refractive index;

medium

light velocity is

is

usually taken to be

considered unity

then becomes 1/v, where

v is

(1).

air, in

The

which the

refractive index

the velocity of light in the

denser medium. Refractive index (usually abbreviated n) is also frequently described in terms of the angle to the

normal made by the incoming light beam (incident ray) and that made by the refracted beam (traveling within the denser medium). Index of refraction in these terms sine of the angle of refraction. It is

perfect cleavage must be set carefully and

blow to the stone along a cleavage direction may easily split the gem. Spodumene is well known for its difficulty in cutting. Even topaz offers occasional problems to the cutter who is not aware of the cleavage direction, because it is virtually impossible to polish a gemstone surface that is parallel to a carefully, as a sharp

cleavage plane.

possible for light traveling from a given

into a less dense

medium,

as, for

medium

example from a

crystal

an angle that the light is totally reflected at the interface, back into the denser medium. The incidence angle at which this takes place is known as the critical angle. This angle has great significance in terms of gem cutting. If the angles at which the gemstone are cut are incorrectly matched to into

cleavage directions. tric

When

equals the sine of the angle of incidence divided by the

indicated in the text.

cleavage, parting

is the premise that light form of waves, like ripples on a pond. The distance between successive crests or troughs of such a wave is known as the wavelength, and the amplitude of the wave is the height of the wave above the median (middle position between crest and trough). In familiar terms, different colors are different wavelengths, and the amplitude is the intensity of the light. Light vibrates at right angles to its direction of motion, and the vibration

basis of crystal optics

takes place in

scale.

The atomic arrangement

The

travels in the

air,

to strike the interface at such

the refractive index of the material, light entering the

stone

may

"leak out" the bottom, causing a loss of

bril-

bottom of the stone, light is totally reflected internally and returns to the eye of the viewer, creating brilliance that is most pleasing and is, in fact, the whole reason for cutting facets on gemstones. The optical properties of gemstones and minerals are determined by the crystallographic symmetry of these materials. For example, isometric crystals have crystal liance. If the angles are correct at the

structures that are highly symmetrical in

all

directions;

OPTICS

the result

Accurate measurements of the optical properties of gems are very useful because optical properties are extremely

amorphous and has no crystal structure) same speed in any direction and is not slowed down measurably in any one direction within the

is

that light traveling in an isometric crystal, or

a glass (which

travels at the

is

OPTICS

material.

Such a material

is

termed isotropic and

is

char-

direction,

is

the extraordinary

ray.

The

refractive indices

acterized by a single refractive index, abbreviated in this

for these rays (directions) are the basic optical

book

ters for a uniaxial mineral,

as N.

However, in all other crystals light is separated into two components. These two rays are polarized, that is, they each vibrate in a single plane rather than in all directions perpendicular to the direction of travel of the light.

The two

rays arising in such crystals are

known

as

and e.

If

listed in this

parameas o

book

the o ray has a velocity in the crystal greater than

the e ray, such a crystal is

and are

17

is

termed positive + ); the (

considered negative (— )

The

velocity.

if

crystal

the e ray has a greater

birefringence in a uniaxial crystal

the

is

difference between the refractive indices for o and

e.

the ordinary ray and the extraordinary ray. All crystals

In biaxial crystals there are three different crystallo-

other than isometric ones cause this splitting of incident

graphic axes, and in addition there are two unique direc-

light

and are termed anisotropic.

The

tions within the crystal that resemble the unique optic

existence of polarized light can be demonstrated

by means of a special prism known after its inventor as the Nicol prism. This contains specially cut pieces of the mineral calcite that are oriented only light polarized

in a single

in

such a way as to allow

plane to pass through.

If

two Nicol prisms are lined up and turned with their polarization directions at right angles to each other, no light

may

pass at

Similarly, a Nicol prism (or similar

all.

The

axis in a uniaxial crystal.

refractive indices of a

Greek letters a and (gamma). Alpha is the lowest y P index, is referred to a direction in the crystal known as X, and is associated with the fastest light speed within the crystal. Beta is an intermediate index, corresponds to the Fcrystallographic direction, and represents an intermebiaxial crystal are designated by the

(alpha),

(beta),

diate ray velocity.

Gamma is the highest refractive index, Z

device) can be used to test for the polarization directions

corresponds to the

of light that has traveled through a crystal specimen or

associated with the lowest ray velocity.

gemstone. This is the basic function of such devices as the polariscope and polarizing microscope. The polarizing microscope is not generally used with gemstones, but instead with tiny mineral grains. Gemologists prefer to

work with

larger polarizing devices, usually 1-3 inch

diameter discs of polaroid

plastic,

mounted

in a

device

In tetragonal and hexagonal crystals there

which

is

is

a unique

either longer or shorter than the

other two axes in the crystal. Light traveling in a direction parallel to this axis vibrates in the plane of the other

two axes. Since the other two axes are equivalent, this vibration is uniform and resembles the light vibration in an isotropic crystal.

If

a pair of Nicol prisms

line with light traveling in this direction in

is

placed

in

such a crystal,

and the prisms are rotated so that the polarization directions are crossed (perpendicular), no light will be seen emerging from the crystal. As a result of the presence of this unique optical direction in tetragonal and hexagonal crystals, substances crystallizing in these crystal

systems

are termed uniaxial.

two directions

in

which

uniformly perpendicular to the direction of

travel.

Consequently, crystals

clinic,

and

triclinic

in

the orthorhombic,

systems are termed biaxial.

mono-

The com-

plete description of the behavior of light in such crystals is

very complex and beyond the scope of this book.

interested reader

is

The axis,

The

works on optical the Bibliography on page 237.

referred to standard

crystallography indicated in

ray in uniaxial crystals that travels along the optic

and which vibrates equally

to this direction,

is

sidered optically negative.

is

the difference

in a

the ordinary ray.

plane at right angles

The other ray, which

vibrates in a plane that includes the unique crystal axis

If

the value of beta

is

is

con-

closer

is termed optically positive. Both refractive indices and birefringence are useful parameters in characterizing and identifying crystals, and both change with composition, the presence of impurities, and may vary even within a single crystal. It should always be remembered that the refractive index is basically a measure of relative light velocity. Every wavelength of light travels through a given medium (other than air) at a different velocity, and consequently every wavelength has its own refractive index. The difference in refractive index with variation in wavelength is

to that of alpha, the crystal

known

as dispersion.

Dispersion

All other crystals contain light vibrates

birefringence in a biaxial crystal

is

between the alpha and gamma index. The acute angle between the two optic axes within the crystal is designated IVand is a useful parameter to the mineralogist. It turns out that if the beta index is exactly halfway between alpha and gamma, the 2 Kangle is exactly 90°. Finally, if beta is closer in value to gamma than to alpha, the crystal

called a polariscope.

crystal axis,

The

crystallographic direction, and

colors.

is

what makes a diamond sparkle with

The difference

light in a

diamond

is

in refractive

quite large.

index for red

As

light travels

vs.

blue

through

a cut gemstone, the various wavelengths (colors) therefore diverge,

and when the

light finally

emerges from the

stone the various color portions of the spectrum have

been completely separated. Dispersion (that

is,

no

is

reported as a dimensionless

units),

but there

is

some degree

number

of choice in

selecting the wavelengths to use as reference points.

convention, the dispersion of a gemstone

is

By

taken as the

difference in refractive index as measured using the

Fraunhofer

B and G

lines.

These are spectral

lines ob-

SOURCES OF DATA USED

18

TEXT

IN

SPECTRAL

in the spectrum of the sun, respectively at 6870 and 4308 A (Angstrom units: one Angstrom is equal to one ten-billionth of a meter. This unit of length is used to

The

describe light wavelengths).

useful in identification or in rapidly distinguishing

served

In

some

no dispersion information

cases,

mineral or gemstone

may have data

ever, the mineralogical literature

refractive index

exists for a

for the

measured at certain different wavelengths B and G wavelengths). In such cases it

(not including the is

means of a Hartman Disper-

possible to calculate the dispersion, by

known

special type of graph paper

sion Net. This

is

as a

a logarithmic-type paper

can plot refractive indices ing the entire useful range.

Such

on which one

wavelengths cover-

at specific

plots are linear

be extrapolated to the positions of the

and can

B and G lines. The

gemstone may be extremely between

two similar gemstones with similar optical properties.

The

gemological literature; how-

in the

optical spectrum of a

principle of the spectroscope

ward. Light we

call

is

fairly straightfor-

white actually consists of a mixture of

combined

the wavelengths in the visible range

all

When

such

in

through a colorless material, none of the light is absorbed, and the white light emerges unchanged. However, some materispecific proportions.

light passes

absorb various portions of the white

als

allowing

light,

other portions to emerge and reach our eyes.

The remaining

portions consist of white light from which certain wavelengths have been subtracted. Consequently,

imately 20 gemstone dispersions never before reported

if a mateabsorbs red, orange, and most of the yellow from the original white light, all that remains is blue and green and

and based on calculations such as are included

the material appears to us as a blue-green color.

B-G dispersion is then simply picked off the graph. Approx-

In

some

cases, as with

in this

book.

opaque or translucent materi-

the gemologist using only a refractometer cannot measure accurate refractive indices; rather the instrument gives only a vague line representing a mean index als,

for the material. Since this

number

what can be expected sometimes been included in the indicates

in

is

useful, in that

routine work,

it

it

has

text of this book. Also,

the refractometer effectively measures all indices of refraction (that

is,

for

all light

wavelengths) simultaneously;

more accurate measurements can be made wavelength

single

is

selected. This

is

be the spectral (yellow) line known as D, which teristic of the

Light

if

only a

universally taken to is

charac-

emission spectrum of sodium.

may be absorbed

differently as

it

passes through

a crystal in different directions. Sometimes the differ-

ences are only

in

degree of absorption or intensity. In

rial

appears red to us because

and green

The

light passing

it

absorbs nearly

through

optical spectroscope

is

all

A

ruby

the violet

it.

a device that separates

white light into a spectrum of component colors, using either a prism or a diffraction grating.

The spectrum

consists of either an infinite (in the case of a prism) or

assemblage of images of narrow slit, each representing a different wavelength. A gemstone placed between the light source and the slit will absorb certain wavelengths. The slit images of these wavelengths are consequently missing from the observed spectrum, and therefore show up as dark lines. The width of the lines depends on the diameter of the slit (which is usually adjustable). Often entire segments of the spectrum are absorbed, and the result is a dark band finite (diffraction-grating type)

a very

rather than a line.

The

light

source

itself

may

not pro-

aimed

other cases, however, different wavelength portions of

duce

the transmitted light are absorbed in different directions,

example, the observed spectrum contains dark lines even though there is no absorbing material in front of the slit. These are known as Fraunhofer lines, named after Joseph von Fraunhofer (1787-1826) who showed them to represent absorptions by elements within

resulting in colors. This

phenomenon

is

termed pleo-

chroism. In the case of uniaxial materials, there are only

two distinct optical directions and the phenomenon is termed dichroism. Other materials may be trichroic, and the pleochroic colors are sometimes very distinct and strong and are useful in identification. The pleochroic colors reported for various

book

in the

order

X/Y/Z,

gems

are presented in this

all

visible wavelengths. If a

spectroscope

at the sun, for

the gaseous outer layers of the sun's atmosphere.

Certain gemstones have very distinctive spectra. In general, an optical spectrum

is

created through the agency

of certain atoms in the crystal structure, which are, in the

separated by slashes.

Since isotropic materials (including glasses) do not

Emerexample, contains chromium; the spectrum of

final analysis, responsible for the light absorption.

affect the velocity or properties of light passing through

ald, for

them

emerald contains very distinctive absorption

in different directions, isotropic

materials never

display pleochroism. Occasionally, however, an isotropic

material

These

may display anomalous colors in

polarized

light.

However, cause is the

effects are generally attributed to strain.

lines repre-

senting chromium, located in the far red portion of the

spectrum. Such minerals as apatite, zircon, olivine, halite,

and idocrase have characteristic

there is abundant evidence that a more likely ordered arrangement of atoms on specific crystallo-

frequently used

graphic

tinguish

sites.

is

in identification.

spectroscope, for example,

is

A

sin-

lines that are

glance through a

instantly sufficient to dis-

between a garnet and a ruby.

STONE SIZES The absorption

spectra of

many gemstones have

not

been reported in the gem literature. In other instances the spectrum has no distinctive or useful features. In both cases the abbreviation N.D. (No Data) has been

yet

used.

hoped

It is

that the next edition of this

contain complete spectral information on

gems

which data are currently not

for

book

will

the rare

all

ILW)

at

3660 A, which

ated by special quartz tubes.

Some minerals react and some

in neither.

excited by

UV

ment

in

LW, some

many

In

light unless

iron

many

in

SW, some

in

cases a mineral

both, is

not

contains an impurity ele-

it

that acts as an activator.

plays such a role in

INCLUSIONS

generated by fluorescent-

is

type lamps, and shortwave (SW) UV, at 2587 A, gener-

ment

available.

UV

19

The element manganese

minerals. Conversely, the ele-

quenches fluorescence

in

most minerals. The

detailed reasons for this behavior are beyond the scope of this book.

Inclusions are crystals of minerals, cracks, healing

and other internal features of min-

sures, bubbles, hoses,

erals that are useful in identification. Inclusions represent

minerals that were floating

in

Luminescence

fis-

solutions from which other

effects are useful in

gemstone

identifi-

cation, especially in certain cases in distinguishing synthetics.

However, luminescence

with other gemological

is

best used in conjunction

tests.

minerals formed; they are bits of liquid and gas bubbles

trapped

in

a mineral as

it

grew; they are fractures sur-

rounding radioactive minerals contained within a host mineral. The world of gemstone inclusions is beautiful, vast,

and exciting, and one

to

which data are continually

being added.

The instrument

for study of inclusions in

gems

is

the

microscope, preferably one with darkfield illumination.

Sometimes inclusions are too small to be resolved with the 30-60X usually reached by stereoscopic microscopes, and magnifications of 200X or more are required. An expert in the field of mineral and gemstone inclusions may be able not only to identify a gemstone and pronounce unambiguously whether it is natural or synthetic but also to indicate the very mine from which it came! Inclusions are the most powerful means of distinguishing the bewildering variety of manufactured stones from the much more valuable natural gems they attempt to imitate. Inclusion information in this book represents a summary of what is in the available literature; information

which this

is

will,

many of the rarer gemstones, hoped, be provided for future editions of

lacking for

it is

OCCURRENCE The occurrences

reported in this book are condensed from both the mineralogical and gemological literature. Where possible an attempt has been made to indicate the general rock types and geological environments in which a mineral occurs. Following this is a listing of specific localities that have been reported, noting, where possible, whether the material found is of major

gemological significance. It

should be remembered that a mineral

from a

locality,

and none of

it is

of

gem

may be

reported

quality (that

is,

and so forth). However, an occasional piece may be encountered that is suitable for cutting, and this is sufficient to establish the material attractive in color, transparent,

in

the literature as occurring in

gem

quality in that

Such possibilities are always open. The main emphasis of this section in the book is to indicate how widespread the material is and from what parts of the world it is best known. locality.

book.

STONE SIZES

LUMINESCENCE This section of the book Certain electrons a mineral

energv

may be

in

atoms within the

crystal structure of

able to absorb energy and release the

at a later time.

This creates a phenomenon known

as luminescence. If the

absorbed energy

immediately, the effect

is

is

released almost

called fluorescence;

if

there

is

from seconds to hours) in the release of the energy the effect is called phosphorescence. The a delay (ranging

excitation energy heat, but the let light.

may be

X-rays, visible light, or even

most widely used energy source

Ultraviolet

(UV)

light

is

is

ultravio-

generated by several two types: longwave

different kinds of lamps, basically of

completed but rather

will,

perhaps, never actually be

will continually

focus on adding

information as obtained.

The

objective

is

to indicate

what constitutes a "large

one" for a given species in question, with respect to cut gems. In some cases catalog information for major museums exists. Much information has been compiled from verbal sources, information in the minds of expert cutters,

museum

curators,

and

collectors. In

some cases

I

have seen no cut examples of a gem in question but have seen references to such gems in the literature or in private communications. Here only an indication can be

SOURCES OF DATA USED

20

provided of expectable

major omissions

gem

in the

sizes.

I

IN TEXT

freely

acknowledge

information presented

in this

portion of the text and hope that interested readers will

make

the next edition

more

useful by providing correc-

museum colSome museums have espe-

Gemstones of major importance lections throughout the world.

exist in

complete collections of rare gems, and these institutions have been mentioned frequently in the text. Abbreviations used for some of these museums are

cially

as follows:

BM: SI:

British

Museum

York)

Royal Ontario Canada)

Academy of Sciences (San Francisco) Museums of Canada (Ottawa, Ontario)

California

National

University

GIA: Gemological

The metric of a gram.

It

carat is

is

Institute of

America

a unit of weight equal to one-fifth

the standard measure of gemstones.

Where

sizes are given in this book without a unit of measurement, the weight in carats is intended. Lowercost cabochons are measured in millimeter size.

(Natural History) (London,

England) Smithsonian Institution (Washington, D.C.)

DG: Devonian Group (Calgary, Alberta, Canada) AMNH: American Museum of Natural History (New

ROM:

CA:

NMC:

HU: Harvard

and additions.

tions

PC: Private Collection LA: Los Angeles County Museum (Los Angeles)

COMMENTS This section contains general comments on wearing characteristics of

Museum

(Toronto, Ontario,

gemstones, miscellaneous notes on occur-

rence, what constitutes high or low quality in the stone,

general availability, and scarcity.

Thermal Properties

Gemologists are severely handicapped in analyzing and identifying gemstones because of necessity (and rather obviously) their testing methods must be nondestructive. This limits the measuring process to the areas of optics, including spectroscopy, luminescence, and so forth, density, and microscopic inclusions. Hardness is not routinely measured on cut gems. Moreover, the instrumentation used in this field must be simple enough to be learned by people with no real scientific training (which is the case with the vast majority of gemologists) and must be affordable.

Much

of the literature of

days reports measurements on gems

different

materials and therefore

Thermal

diftusivity

heat flow in a material.

some of the heat energy

is

not especially

is

a measure of the velocity of

If

heat

(to a

is

applied to a substance,

degree that depends on the

specific heat of the material) goes into raising the tem-

perature of the substance.

The

rest of the heat

diffuses

away from the point where the heat

applied.

The higher

rial,

gemology these

made

gem

useful for identification purposes.

the faster

it

energy being

is

the thermal diffusivity of a mate-

will pass

heat energy from one point

to another.

Thermal conductivity on the other hand,

with various

is

a ratio and

kinds of advanced instrumentation, including ultraviolet

relates the flow of heat through a given thickness of

absorption spectroscopy, X-ray fluorescence analysis,

material to the temperature difference across this thick-

and even electron paramagnetic resonance. This is well and good for the literature but is of little practical value for the working gemologist and/or appraiser.

ness.

Therefore,

(isometric or amorphous) materials.

it is

convection (the creation of currents

pot of boiling water), and conduction. of heat transfer

is

in

Thermal

testing

is

thermal

inertia.

The

applied. This

is

the

amount

materials.

quickly the sur-

The

higher the thermal inertia,

is

why

when

heat

is

materials, such as plastics, that have

warm

to the touch

— body heat

while stone objects feel cold.

Thermal

inertia

is

a directional property but lends

mean The various diamond probes (such as those made by the GIA, Rayner, Kashan and Ceres Corp.) on the

out to be

itself to

simple instrumentation for measuring a

value.

market take advantage of

of heat required to raise

this fact.

Such probes consist

a

of a temperature-difference sensor (a thermocouple) and

little in

an adjacent thermal source (resistance heater) surrounded

Celsius. This that varies

of

rapidly raises the surface temperature of such materials-

lined below:

Specific heat

a measure of

a low thermal inertia feel

others are not as useful, as out-

one gram of a substance one degree constant for a given substance but one

is

the slower the surface temperature will rise

the one that can most easily be measthis turns

inertia

of heat into the material.

a

The latter method

the most relevant to solid materials at

ured with simple instrumentation;

The symmetry

usually the same, but

face temperature of a material can be changed by a flow

that is, gemstones. There are four thermal properties of potential interest, three of which are mathematically interrelated. However, the best one

gem

is

made on gem how

with direction have been

room temperature,

for

direc-

is

very few measurements on the variation of conductivity

method of gemstone analysis. One such method the measurement of thermal properties. Heat energy may be transferred by radiation (for exam-

technical

ple, sunlight),

turns out that thermal conductivity

optical and thermal properties

important to explore the potential of any possibly diagnostic, inexpensive, simple, and nonis

It

tional, just like refractive index, in all but isotropic

is

21

3

THERMAL PROPERTIES

22

by an insulated probe housing. Care must be taken in using such instruments to prevent drafts from affecting

The probe

the readings.

tip

placed against the mate-

is

gemstone facet) and a meter reading is obtained in about one second. This reading can be related to thermal inertia. The commerrial

being measured (that

TABLE

1

is,

Thermal Properties

.

a

of

Gem

Materials, Synthetics,

Gem

Materials, Synthetics,

diamond

inertia). Difficulties

small

Thermal

Specific

Heat (cal/gm °C)

1.6-4.8

12

0.215 b

Periclase (synthetic] Corundum: c axis a axis c axis Topaz: a axis

0.1

0.2* 0.2*

mean, Gunnison, Colorado Colorado

Kyanite: c axis

b axis

mean, Minas Gerais,

Brazil

Itabira, Brazil

Spinel: locality

unknown

Madagascar Fluorite: locality

unknown

Rosiclare, Sphalerite:

Illinois

Chihuahua, Mexico

Sillimanite: Williamstown, Australia

Andalusite: Minas Gerais, Brazil Pyrophyllite:

North Carolina

Japan San Benito County, Gahnite: Colorado

Jadeite:

California

b 1

0.0834 b 0.0772 0.060 c 0.0446 0.0269 0.0459 0.041

b

0.0396 0.0338 0.0270

b

0.0281 0.0227 0.0219 0.0227 0.0304 0.0217 0.0181 0.0194 0.0159 0.0110 0.0103

Magnesite: Transvaal

00139

Rutile:c axis

0.0231

0.206 0.206 0.206 0.2* 0.2*

0.136 0.201 0.201 0.201

0.2*

0.196 0.196

Dolomite

00132

0221

Olivine (peridot, Fo 86 Fai 4 )

0.0115 0.0126 0.0124 0.0117 0.0112 0.0119 0.0109 0.0105 0.00994

0.2* 0.2*

axis axis axis

axis

mean, Jessieville, Arkansas Spodumene: Maine York

Madagascar

Keystone, South Dakota

Quebec

Tremolite: Balmat,

Ontario,

New

Metals

at

Thermal

(gm/cm 3)

[cm 2 /secJ

3.52 a 3.17 a 3.575 a 4.0 a 4.0 a

3.79-1 1.4

b

York

Canada

Amblygonite: South Dakota Zircon: Australia Enstatite(En 98 Fs 2 ): California Bronzile (En 7 8Fs 22 ): Quebec

4.0 a

3.53 a 3.531 4.915

366 a

3.196 3.350 4.163 2.993

0.2*

Chihuahua, Mexico Crestmore, California

Talc,

Some

Diffusivity

2829

0.0133 0.00969

Grossular: Connecticut

Elbaite:

problem.

Density

0.206

00135

Virginia

New

as

0.2*

0.0122 0.0135 0.0134 0.0124 0.0264 b 0.0264 c 0.01 40 b 0.01 60 c 0.0184

Diopside:

well

0.169 0.216 0.216 0.220 0.220 0.115 0.203 0.202

0206

0.01 32 b

a axis

Quartz: c c a a

to avoid this

3.66 a 3.102 5.143 3.63 a 3.633 3.18 a 3.186 4.103 3.162 3.102

0.236 0.189 0.189 0.189 0.196 0.196 0.196 0.196 0.196 0.196 0.196 0.196

mean,

with very small

Room

Temperature

Thermal Inertia

[cal/cm 2

°C sec h )

and Simulants

Silicon carbide (synthetic)

Hematite:

gems

and Simulants as

Diamond

Pyrite:

may be encountered

stones, but the instrument can be calibrated against

Conductivity

(cal/cm°Csec]

Material

probes were developed specifically to distinguish (with a very high thermal inertia) from its imitations, such as cubic zirconia (with much lower thermal

cial

0.221

0.210 0.210 0.2*

0.140 0.2* 0.2*

0.822-1 42

0.339 0.154

0369

0.101

0262 0252

0.0937 0.0728 0.0632 0.0381 0.0684 0.0562 0.0539

0.281

0.222 0.177 0.138 0.176 174 0.171

3.008 3.025 4.633 3.209

0.0166 0.0153 0.0188 0.0193 0.0190 0.0578 0.0509 0.0270 0.0308 0.0354 0.0214 0.0208 0.0146 0.0209 0.0166 0.0202 0.0200 0.0186 0.0177 0.0197 0.0167 0.0334

0.158 0.153 0.148 0.133 0.124 0.126 0.120 0.118 0.107 0.105 0.102 0.0873 0.102 0.0992 0.135 0.102 0.0990 0.0979 0.0967 0.0898 0.125 0.117 0.0854 0.0912 0.0978 0.0923 0.0923 0.0802 0.0911 0.0893 0.0889 0.0878 0.0854 0.0839 0.0850 0.0839 0.0821

3365

00148

00818

4.2 a 4.2 a

4.244 3.617 3.548 3.318 2.65 a 2.65 a 2.65 a 2.65 a 2.647

3.155 3.270 3.394 2.857

3469 3.134 2.804

2981

0.0461

0.0310 0.0358 0.0288 0.0313

00324 0.0646 0.0339 0.0289 0.0343 0.0242 0.0160 0.0100

00198 0.0291

8 2

Material

Spessartine: Haddam, Connecticut Datolite: Paterson, New Jersey Anhydrite: Ontario, Canada Almandine: Gore Mountain, New York Staurolite:

Georgia

Augite: Ontario

Pyrope: Navajo Reservation, Arizona Andradite: Ontario, Canada Smithsonite: Kelly, New Mexico Beryl: c axis

Thermal

Specific

Conductivity

Heat (cal/gm °C]

(cal/cm°Csec)

0.0131

Flint:

Petalite:

000627 000856

mean, MinasGerais, Brazil Calcite: Chihuahua, Mexico Axinite: Baja California

New

Jersey Rhodochrosite: Argentina Prehnite: Paterson,

Brownsville, Ohio Epidote: Calumet, Colorado

Rhodesia

Clinozoisite: Baja California

Idocrase: Chihuahua, Mexico Sphene: Ontario, Canada lolite:

Madagascar

Zoisite: Liksviken,

Norway

Aragonite: Somerset, England Microcline: Amelia, Virginia Ontario, Canada Albite (Ab 99 An,): Amelia, Virginia Serpentine (lizardite): Cornwall, England Orthoclase: Goodspring, Nevada Sodalite: Ontario, Canada Lepidolite: Dixon, New Mexico Anorthite (Ab 4 An 96 ): Japan Fluor-apatite: Ontario, Canada Chlor-apatite:

Snarum, Norway

Labradorite (Ab 46 An 5 4): Nain, Labrador

Georgia Apophyllite: Poona, India Barite:

Leucite:

Rome,

Italy

(General Electric) Hyalite: Spruce Pine, North Carolina Glass: obsidian ordinary flint (lead) very heavy flint (lead)

Vitreous

silica

3.306 2.953 3.584 2.618 3.413

0.184 0.2* 0.2* 0.2* 0.2* 0.2*

2.391

3.360 3.342 3.525 2.592 3.267 2.827 2.556 2.558 2.606

0.188 0.2* 0.2*

0.209 0.194 0.194 0.202 0.2* 0.2* 0.2* 0.2*

0.00460 0.00401 0.00328 0.00331 0.00365 0.00319 0.00331 0.00274 0.00325 0.00290 0.00330 b 0.001 0.001

2.701 2.721

0.2* 0.2*

000600

2.601

2.583 2.326 2.844 2.769 3.215 3.152

0.196 0.195 0.195 0.2*

2.701 4.411

0.113 0.2* 0.2*

2.364 2.483 2.205 2.080

0.201 0.2* 0.2*

b

0.1

b

1

[cm 2 /sec]

3.275 3.746 3.746 4.362 2.70 a 2.70 a

0.218

0.00574 0.00576 0.00558 0.00650 0.00513 0.00535 0.00621 0.00590 0.00553 0.00558 0.00553

[gm/cm 3 ]

3932 3689

0.2* 0.2* 0.2* 0.2* 0.2* 0.2* 0.2* 0.2* 0.2*

b

Diffusivity

3.987 2.996 2.978

0.187

0.00759 0.00738 0.00612 0.0104 b 0.00953 0.00858 0.00767 0.00854 0.00731 0.00886

a axis

0.2* 0.2*

0.00811 0.0106 0.0114 0.00791 0.00828 0.00913

Thermal Density

7

a

0.117

2.4 a 3.5 C 4.5 a

0.0102 0.0177 0.0204 0.0101 0.0112 0.0140 0.0101

0.00984 0.00701 0.0243 0.0193 0.0176 0.0145 0.0116 0.0145 0.0111

Thermal Inertia

[cal/cm 2

°C

0.0804 0.0798 0.0796 0.0789 0.0782 0.0773 0.0754 0.0744

00731

00842 0.0750

00718 00713 00712 0.0710

00695

00169

0.0681

0.00919 0.0179 0.00854 0.00863 0.00845 0.0126 0.00785 0.00906

0.0654 0.0640 0.0621 0.0620 0.0607 0.0580 0.0579 0.0562 0.0554 0.0541 0.0540 0.0539 0.0534 0.0528 0.0512 0.0467

00126 0.0119 0.0105 0.0107 0.0107 0.0129 0.00807 0.00737 0.00522 0.00539 0.00676 0.00639 0.00699 0.00551 0.0074 0.0070 0.00688 0.00440 0.00228

sec'']

00454 0.0451

0.0444 0.0399

00396 0.0369 0.0379 0.0347

00398 00272 0.0251

Metals

Copper Silver Silver Silver

Gold

1

0.927

00%

69%, gold 31% (weight) 34%, gold 66% (weight) 1

00%

Aluminum Platinum Platinum,

10%

0.092 0.056 0.048* 0.040*

1.00

iridium

0.237 0.152 0.707 0.485 0.166 0.074

0.031

0.214 0.032 0.032*

8.89 10.5 12.3 15.5 19.3

1.13 1.70 0.401

2.7

0.839 0.242 0.107

21.4 21.6

0.245

118

0.871

0767 0.374 0.307

0650 0529 0.337

0226

Source: From D. B. Hoover, The gem diamondmaster and the thermal properties of gems, Gems & Gemology, Summer 1983: 77-86. © 1983 Gemological Institute of America Reprinted with permission. Note: Unless another reference is indicated by a superscript letter, the values for conductivity and density were taken from K Horai, 1971, Thermal conductivity of rock forming minerals, Journal of Geophysical Research 76(5): for specific heat from R A. Robie and D R Waldbaum, 1 968, Thermodynamic properties of minerals and related substances at 298.1 5 degrees K and one atmosphere pressure and at higher temperatures, U.S. Geological Survey Bulletin 1 259. * = assumed value: not found in the literature a R. Webster, 1982, Gems, 3rd ed. Hamden, Conn.: Butterworth & Archon. b Chemical Rubber Company, 1966, Handbook of Chemistry and Physics, 47th ed Boca Raton, Fla.: Chemical Rubber Company c S. R Clark, 1 966, Handbook of Physical Constants. Memoir 97 Boulder, Colo.: Geological Society of America.

23

24

THERMAL PROPERTIES Table

1

was compiled by

Dr.

Donald Hoover of the

U.S. Geological Survey and is generally arranged in order of decreasing thermal inertia. If accurate, quantitative

cally to separate

diamond from other stones. New devices measurements will repre-

specifically designed for such

sent the next generation of thermal meters. Surface qual-

probes become widely used, thermal inertia could become a very useful, easily measured parameter for gem-

as degree of crystallinity

stone analysis.

cially in solid solution series).

Note: Quantitative measurement of thermal inertia

be

difficult using

may

instruments that were designed specifi-

ity

(degree of flatness and polish affects readings, as well )

and chemical composition

(espe-

Figure

1.

Three-dimensional color system.

(From Precise Color Communication: Color Control from Feeling to Instrumentation, p. 8; courtesy of Minolta Camera Company, Ltd., Japan.)

black

Figure 2. Color solid. (From Precise Color Communication: Color Controi from Feeling to Instrumentation, p. 9; courtesy of Minolta Camera Company, Ltd., Japan.)

Cr roma Figure 3. Munsell color wheel. (From Precise Color Communication: Color Control from Feeling to Instrumentation, p. 19; courtesy of Minolta Camera Company, Ltd., Japan.)

/I

11

/4

/6

/8

/10

l\l

9/

8

7/

6

[

Value 4. Munsell value and chroma hue 5G. (From Precise Color Communication: Color Control from

Figure

5/

for

Feeling to Instrumentation, p. 17; courtesy of Minolta Camera Company, Ltd., Japan.)

4/

• • 1/

/14

GREEN YELLOW

GREEN J&£&'--

BLUE GREEN

BLUE

PURPLE

BLACK Figure 5A. Lab color space as conceived by Richard S. Hunter

520

\540

\5( i0 0.6

6

500

^580

4

\600 620

V650 ^770 nm 2

480 \

47

380^^ 450^^ 2

4

6

08

Figure 5B. The CIE chromaticity diagram (1931). All the fall on a horseshoe-shaped line called the spectrum locus. These colors are indicated by their wavelengths (in nm). (After F. W. Billmeyer, Jr., and M. Saltzman, Principles of Color Technology, Wiley, New York, 1981, p. 125.) spectral colors

>7

2.5PB

TABLE

3.

7

\\

\ \

notation

LW

I

R

YR

V

GY

G

BG

e

PB

1

5

7

8

7

6

5

4

4

4

4

2

9

12

15

13

11

10

9

9

9

9

chroma

\

Munsell

Yl

chroma

5PB"

Munsell (chroma C) and L'a'b* (chroma c") notations

Munsell hue

i

5RP

f

P RP

U

Figure 6. L*a*b* and Munsell notations (hue, value). For extremely small or large a*b* values, multiply or divide them by an appropriate amount before plotting

and reading the hue

values. (From Precise Color 3

15

17

22

22 19

16

15

13

13

13

13

4

19

22 25

29

29 25

22

20

17

17

18

18

26

6

27 30 34 38 42 45 43 39 34 31

28

26

26

27

8

37 41 46 50 56 59 58 51 45 42

38

34

34

36 35

10

46 51 57 63 70 74 73 65 56 53 51 47 44 40 41 44 45 44

12

55 62 68 76 84 88 87 77

14

64 73 79 90

16

84

94

101

Communication: Color Control from Feeling to Instrumentation, p. 19; courtesy of Minolta Camera Company, Ltd., Japan.)

48 55 53 51

98

66

109

75

62 60 Source From Precise Color Communication Color Control from Feeling to Instrumentation, p 19, courtesy of Minolta Camera Company. Ltd Japan Wote In columns with two digits, left figures are for hues 1-5 and right figures are for hues 6-10

Color Measurement

and Specification One

of the great challenges of

ment

gemology

is

Lightness (also called value)

the develop-

and reproducimeasuring and specifying gemstone

of an accurate, simple, consistent,

ble technique for

colors. Until the mid-1980s

is

a scale with white and

black as endpoints and shades of gray

however, that

all

in between. Note, chromatic colors can also be scaled as

progress in this direc-

to lightness as a function of their total reflectance. Light-

was made, despite the appearance and widespread promotion of various color-chart systems. None of these systems work, chiefly because they do not adequately cover the total range of gem colors, do not have enough detail in the areas they do cover, and the color-chart

ness can be visualized in terms of a vertical axis with

little

tion

white at the top and black at the bottom (see Figure. Saturation (or chroma)

is

a measure of the

vertical sections of three-dimensional color

not of sufficiently high quality to prevent variations

ure

is

1).

of

hue in a color, that is, its vividness, or how much it differs from a gray of the same lightness. Chroma can be seen in

materials (whether printed colors or transparencies) are

production runs. The ideal solution

amount

in

a gemstone color-

2).

A

space (Fig-

section along a specific radial direction of the

color circle

is

designated as a specific hue. Lighter shades

imeter; however, such an instrument must deal with the

of this hue are near the top of the section, darker shades

unique optical properties of gems, including such factors and pleochroism, which make gemstones extremely difficult specimens for instrumental measurement.

at the

bottom. The chroma (vividness) of the hue increases moving outward from the central axis. Figure 2 shows that the range of chroma varies with both hue and lightness; this makes the color solid an irregular shape, rather

as brilliancy

The science of colorimetry is well established all

areas of endeavor where color

paint, plastics, textiles,

is

and other

in

almost

important, such as industrial

than a simple ovoid or sphere.

Color specification can be achieved by subdividing

and con-

sumer materials. Objective instrumentation is now routinely used in these fields, but before such instruments were available people had to rely on visual systems for specifying color, namely, color charts. These charts are sections of what we may refer to as three-dimensional color space. These three color dimensions are termed hue, lightness, and saturation. Hue is the attribute we are describing when we speak of red, yellow, green, blue, purple, and other hues intermediate to adjacent pairs in this series. These hues can be readily visualized in terms of a color wheel (see Figure 3).*

the color solid into smaller units and giving each a

or set of numerical coordinates. This results in a cation

ways

known

as a color-order system.

there are also

Some

many

color-order systems.

of the color-order systems created during the

early decades of this century (including those of Munsell,

Ostwald, Ridgway, and others) were represented by charts

made

of paint colors coated on paper. These were used by architects and designers for selecting and specifying

and quality conand by biological scientists for color classification of thousands of specimens of flora and fauna. Thus the need for accurate color measurement and specification was firmly established before instruments and related color-order systems were available. Some of these older systems (Ridgway in biology, Ostwald in architecture) colors, by industry for color selection

1

Jr.,

and 22-year veteran of Munsell Color Co., Inc. both president and technical director), to whom the writer is deeply

private color consultant (as

There are many

to subdivide the color solid, and, not surprisingly,

trol,

Substantial portions of this text were provided by W. N. Hale,

name

classifi-

indebted.

•Figures 1-6 and Table 3 will be found in the preceding insert.

are

25

still

in

use today.

COLOR MEASUREMENT AND SPECIFICATION

26

Perhaps the most popular and widespread of the chartis the one devised by A. H. Munsell and extensively revised by the Optical Society of America (OSA) in 1943. The Munsell hue scale is based on five hues equally spaced around the hue circle (red, yellow, green, blue, purple) and intermediate hues type color-order systems

(yellow-red, green-yellow, blue-green, purple-blue, redpurple). The major hues are abbreviated R, Y, G, B, P and the intermediate hues YR, GY, BG, PB, RP (Figure 3). Further subdivision results in forty hue charts in the Munsell Book of Color. Colors appear on these charts at value (lightness) intervals of one unit from 2 to 9. Chroma is represented in whole units ranging from 2 (near-gray) in two-step intervals up to as high as 14 and 16 for the most vivid colors (Figure 4). The notation system is decimal, allowing colors to be specified as accurately as required. Munsell color books are available in both matte and high gloss finish, with the latter having about fifteen hundred colors.

published for such colors, the numbers are valid only

which the measurement data were computed. CIE color space is visually nonuniform. A more uniform color space makes specification of tolerances and small color differences more meaningful and is therefore more useful to science and industry. Extensive research has been done to produce mathematical transformations of CIE data into a more visually uniform color space. In 1942 Richard S. Hunter designed a filter colorimeter for the measurement of opaque surface colors and with it the Hunter color-order system. This is a transformation of CIE data using simple equations that were incorporated into the computational elements of the instrument. Hunter space was of the "opposite-hue" or "opponent-hue" type as shown in Figure 5. When Hunter

for the light source for

a attribute tive,

is

positive, the color has redness;

when b

greenness. Similarly

is

when

nega-

positive the color has

the Swedish Stand-

when negative, blueness, The third Hunter was L for lightness. Equal steps along the three scales (L,a,b) were intended to represent equal visual

ard Natural Colour System) have certain similarities.

steps in the several color directions, permitting color

All these color-order systems (including the

recent

German standard DIN 6164 and

Color sampling

is

more

along lines of constant hue (or a simi-

Thus corresponding colors on adjacent hue charts become visually farther apart as they become progressively more saturated (that is, move further away, radially, from the center of the color circle). This means that the most vivid colors are more distant from each

yellowness, attribute

differences to be simply

computed by the formula:

lar metric).

AE^yjAL Where It is

more. The color charts for use with gemstones are inadequate because they do not have sufficient colors in the

ments

vivid color regions to

which they extend, and they do not

gemstones. In addition, opaque paint colors do not look like transparent gemstones, even when they are, in fact, the

same

colors.

A

major step forward came in 1931 with the international adoption of the Commission International d'Eclairage (CIE) system, resulting in greater interest in color measurement and specification, especially by colorimetry. The CIE system included standard illuminants (incandescent, sunlight, north daylight) a standard observer, and standard response functions of the visual system.

The CIE continues

human

as the principal inter-

national organization in the field of color research and

standardization and since 1931 has

made important

improvements and additions to the original concept. The color industry was built around research and development of spectrophotometers and colorimeters capable of making measurements and reporting data in CIE terms. However, this created a problem with existing color-order systems. Such systems are necessarily spaced visually for their appearance under a specific light source; visual spacings and overall appearance will be accordingly altered

if

other sources are used.

If

CIE

data are

Greek

2

+ Aa + Ab\

letter delta {A)

+

E

denotes color

difference.

other than less vivid ones, often by a factor of five or

extend far enough. Opaque colors on paper simply cannot be produced to the color ranges of vivid, transparent

the

1

common practice today for color-measuring instruto include

Hunter color notations as a readout

option for expression of measurement results. Although material color samples were never produced to illustrate Hunter color space, the nearly uniform visual spacing

became

very useful for describing color specifications

and tolerances in industry and contributed importantly to the sale and use of these instruments. Work continued in the CIE and elsewhere to provide a color space with even better visual color spacing, resulting in the 1976 recommendation for the use of CIELAB space. This is similar to Hunter space, is a mathematical transform of CIE data, and is plotted on rectangular coordinates (see Figure attributes are designated

L*

6).

CIELAB

(L-star), a* (a-star)

color

and b*

(6-star) to distinguish them from Hunter and have the same nominal meanings. As with Hunter, CIELAB is a standard readout on current instruments. An even newer opponent-hue system, developed by the Optical Society of America and called Optical Society of America-Uniform Color Spacing (OSA-UCS), is not only an improvement over Munsell spacing but is 2

also a direct this writing

CIE

transform.

The OSA-UCS

colors (at

558 colors, available as 2 x 2 inch samples)

are in scales with intervals of two units in chromaticity

and one in lightness; a prototype OSA color collection produced in Denmark shows chromaticity scale intervals of only one unit, with lightness increments of 0.5

COLOR MEASUREMENT AND SPECIFICATION and over two thousand colors. The OSA-UCS colors are the best example of uniform color spacing produced to date and will probably appear soon as a readout option on instruments.

Some

gemologists have tried, without success, to use

tent as the integrating sphere/fiber optic system of

Rennilson and Hale. Also, the conversion of

conversion

may

arise

due

capacity of this device.

Instrument makers have not perceived the gem field to warrant the costly research and development necessary

when

The

ing color charts in

exist-

and simplistic optical devices currently

use by gemologists are severely limited in accuracy

trying to illustrate

enough

to

searchers to modify this instrument for gemstone col-

literature, the

beam

size

and adding a

glass plate to

real is

ogy for

purpose of

An improved version of this instrument, also using the Minolta colorimeter, was devised by W. N. Hale and J. J. Rennilson. This replaces the glass and mirror with a

how they were obtained and the new technology for gemology and

NOTES 1.

Hale Color Consultants,

2.

MD. 21131. In CIELAB

A gemstone mounted

in the

sphere wall. This

is

sufficiently accurate

and repeatable

for

C

(

is

likely that this

tion will totally revolutionize the

3.

4.

ing order

and objective

kind of instrumenta-

gemstone

field, bring-

reality to a chaotic

system of

vague and often obsolete terminology.

The Rennilson-Hale instrument was not yet available when the table of gemstone measurements (Table 2) was book; the Pettijohn instrument was illuminating and viewing geometry produces results that are neither as accurate nor consis-

prepared for

this

therefore used.

The

is

calculated from a* and

2

(both representative of standard daylight in slightly

different form). It

chroma

Chroma = C* =\/a* +

gem-

The data readout is in CIE data Y,x,y) and CIELAB {L*,a*,b*), for CIE standard illuminant D65 or stone work.

1505 Phoenix Road, Phoenix,

irradiated

colorimeter, with patented illuminating and collection

geometry

Inc.,

terminology, b* as follows:

2-mm light beam from below. Light reflected from gem is mixed with that transmitted through it and

picked up by a detector outlet

and objective

The numbers them-

the gemstone marketplace.

by a the

chapter and these measure-

to

be the xenon flashlamp built into the unit rather than an independently measured white standard.

is

compared

most species.

selves are considered less important in this context than

implications of this

plate centered within the sphere

this

color characterization of gemstones.

an understanding of

on a clear

small

nomenclature, direction and methodol-

this arrange-

small white-lined integrating sphere.

is

scientific, accurate, reproducible,

through the stone to the sensor. However,

measurement

tabulated numeri-

to establish, for the first time in the gemological

light passing

dictates the "standard" illuminant for

The

to the actual variation in color exhibited by

hold the sensor and a small mirror to reflect

ment has proven insufficently accurate and repeatable to be a viable solution. Moreover, the mirror arrangement

5

stone species, but this degree of error

ments

by reducing the

gemstones by photography and

must therefore not be considered accurate establish benchmark points for specific gem-

The

the Minolta sensor unit for specific use with gemstones

to the limited data storage

Further errors are inevitable

cal color data

lower-cost portable colorimeter motivated several re-

A first attempt by Dr. Richard Pettijohn adapted

4

printed reproduction on paper.

and usefulness. The recent marketing by Minolta Camera Co. of a

orimetry.

CIELAB

data to Munsell notation (see Figure 6 and Table 3) was done by the Minolta DP-KX) microcomputer; 3 errors in

existing color instrumentation to characterize gemstones.

to devise specifically applicable instruments.

27

b*

2 .

Invaluable assistance in converting measured L*a*b* values to Munsell numbers, along with many valuable suggestions, was provided by Richard E. McCarty of Silver Spring,

Maryland. Color data on gemstones reported herein are in the form of CIELAB readout and corresponding Munsell notation. The conversion to Munsell numbers are direct CIELAB conversions. No attempt has been made to simplify the resulting Munsell values in accordance with the limited range of actual Munsell color samples. This approximation is left to the reader.

5.

As many as possible of the gemstones photographed in this book were measured with the Pettijohn-Minolta colorimeter; these gems are cross-referenced by notation in the section of color plates at the back of the book, and the tabulated color information herein refers to specific gemstone colors, shapes, and weights, facilitating easy correlation with the photographs.

COLOR MEASUREMENT AND SPECIFICATION

28

TABLE

Adamite Andalusite

Shape

Location

dark green light green

0.63

— —

Tanzania Mapimi, Mexico

brown -green

9.55 4.72 2.92

Color

brown-green medium browngreen

Amblygonite Apatite

yellow light yellow light yellow violet violet

yellow-green yellow dark blue medium blue gray-blue

Brazil

round

Brazil

fancy

Morocco

75

round

Brazil

antique

Brazil

80 95

emerald cut hexagon rhomboid

Maine Maine

Canada

antique

Mexico

round

Brazil Brazil

Burma

dark blue

2.40

oval

dark brown pale blue

066

medium brown medium

blue

71

oval

1.07 1.19

blue

'

-7.7 -0.6 -3.5

6GY

5.5/1.7 8.2/3.8 5. 7Y 5.7/6.9 1.9Y 5.9/2.1 2. 8Y 3.7/2.9

9.1

7.

3. 2Y

26.0 49.0

1.0

14.1

1.6

20.0

2.7 5.3

50.0

2.

1Y 7.4/7.4

114

5.

3YR

-3.5

20.0

6.0Y 9.4/2.8

10.3 6.0

-15.0

3.

1P 7.0/4.0

-7.2

4.

9P

'

6.99 10.10 24.6 0.59 1.02 8.05 8.70 0.55 0.86 0.77 12.40 2.87 1.09 1.07 1.45 8.0

light

Benitoite

Brazil

antique

dark blue

green dark green medium green Axinite

emerald cut

round round round round emerald cut round pear round round round

light

Munsell

L*a*b*

56 82 58 60 38

086

light

Anglesite

Color Measurements

Weight

Gemstone Actinolite

2.

?

31 61

Brazil Brazil

Madagascar Baja, Baja,

75 68 83 34 52 50 42

Mexico Mexico

76 42

6. 7Y 9.

8.2/5.0

7B 3.3/10.4

4.6B 5.1/7.8 4.

6BG

4.9/1.5

5.3GY 4.1/1.6 0.1G 3.0/3.2 8.

5GY

6.0/2.4

7.0BG 7.5/4.2 10. OR 4.1/2.6

-29.1

61

-2.7 -17.5

2.8PB 6.0/4.3

38 54 80 65 85 55 70

-6.0 -8.0 -4.0 -11.0 -6.9 -9.0 -3.5 -18.0 -12.0 2.6 -55.0 15.0 -41.7 2.5

5.

46

-73.2

9.1

8.

-60.0 -23.5

15.0 0.5 6.5 13.2

6.0G 3.9/1 1.0

21.1

3.

3.1

2.

-1.0 -0.5

California

Coronel Murta

California

10.7 9.3 14.2 20.6 -7.6 5.6 4.5 -27.0

7.5/2.0

1.9GY 6.7/4.5

8YR 2.0/4.2 4P 8.4/2.0 6. 6PB 6.7/6.3 7.1 PB 4.5/7.0

21

85 68 46

California

-11.3 32.1 -6.2 36.0 -10.2 -406 -22.8 -25.9 -1.0 -7.5 -6.2 9.8 -16.4 12.3 -11.2 11.9 -4.1 -20.2

7.9/2.1

8.4

4. 4.

Beryl

Aquamarine

Mine, Brazil

dark blue dark blue

antique

Brazil

medium green

0.88

emerald emerald pear round emerald emerald

dark blue-green

1.35

emerald cut

medium medium Emerald

66.53 45.40 18.08 21.80 0.32

light

blue

blue

pale green light

yellow-green

—

cut cut

Brazil Brazil

Africa

cut cut

Colombia Colombia Chivor Mine,

8B 3.7/2.3 5PB 5.3/2.8 8. 2B 7.9/2.7 2. 6PB 6.4/4.4

9G 8.4/2.2 0G 5.4/10.1 2. 0BG 6.9/8.0

8. 6.

Colombia

dark green blue-green light green light yellow-green greenish-yellow blue-green dark yellow medium yellow dark orange light

Green

beryl

Golden

beryl

golden orange golden orange medium dark golden orange Morganite

pink

peach peach Brazilianite

yellow-green

Cassiterite

light

brown

yellow Calcite

dark brown-orange

—

Muzo

Mine,

Colombia Zambia

triangle

Brazil

19.09 4.54 20.00

antique

Brazil

emerald cut emerald cut

Brazil

3279

antique antique pear

Brazil Brazil

40 68 65 75 70 68 63 74 45

Brazil

61

oval

Brazil

emerald cut

Africa

50 70

17.33 6.92 9.06

square square

Brazil

81

Brazil

oval

Brazil

80 90

2.00 14.25 2.88 12.55

oval

Brazil

round round round

Bolivia

1.96 11.25 18.42

18.60 18.98 40.98 3.90

emerald cut emerald cut round

Nigeria Brazil

Brazil

Bolivia

Baja,

Mexico

-3.5 -5.1

-9.3 -5.2 -8.2 -6.0 17.4

10.2 4.6 10.4 8.9

39.0 34.2 71.7 42.0 41.0 70.0

-0.9

3G

4.5/13.6

7BG 6.7/4.6 3GY 6.4/1.0 2. 0GY 7.4/1.9 2.

4.

8.

7

2GY 6.9/3.2 0G 6.7/1.0 3Y 6.2/5.4 0Y 7.3/4.8

9.9YR4.4/11.5 4. 3Y

6.0/6.0 4.9/5.9 0.2Y 6.9/10.7 4. 5Y

2.8RP 8.0/1.1

10.0 11.8

9.

7R

7.9/2.7

1.3YR 8.9/2.6

2Y 7.3/2.4

74 47 82

-1.9

17.0

5.

7.5

266

9.

1.3

41

23.2

33.0 58.4

7.3YR4.0/10.1

3YR 4.6/4.3 1.8Y 8.1/4.9

COLOR MEASUREMENT AND SPECIFICATION

Gemstone Calcite-Co Child renite

Color

Weight

Shape cushion round

Spain

7.80 6.19

oval

Sri

oval

Sri

7.51

round round

Sri Sri

oval

Brazil

antique

Brazil

9.30 21.30

emerald cut

Sri

oval

Sri

11.49 12.02 13.59

oval

Brazil

round free form

Sri

dark rose pink

3.40

peach

1.37

brownish-green

Brazil

Munsell

L*a*b*

Location

29

20 74

ATA -16.4 19.0

9.3

3.8R7 .3/4.5

47 38 54 54 67 49

-3.6

28.8

6.7Y4 6/4.0

5.8 2.6

363

3.1RP

1

.9/1

9

1

Chrysoberyl

medium brown brownish-yellow green-yellow yellow-brown dark greenish-

7.04 11.84 13.25

Lanka Lanka Lanka Lanka

2.8

48.1

-6.0

36.3

1.3Y 3.7/5.4 1.9Y 5.3/4.1 4. 2Y 5.3/5.8 2.3Y 6.6/7.1 7.7Y 4.8/5.1

6.7

42.5 31.3

1.2Y 4.2/6.5 7.0Y 5.8/4.4

-0.4

27.7 40.4

yellow

brown dark greenish-

Lanka Lanka

43 59

-4.9

yellow

lemon yellow Chrysocolla

Cinnabar

greenish-yellow medium blue red

1.37

fancy

Lanka

Arizona Charcas,

-9.4

72 50 39

-7.1

30.8 41.3

-36.0

-9.5

0.9GY 7.1/4.2 8. 0Y 4.9/5.7 5.9BG 3.8/7.4

11

37.4

36.5

1.1YR 1.0/9.4

59.0

7.3YR3.5/10.3

Mexico Clinohumite

orange

1.52

emerald cut

USSR

36

24.8

pink-violetish red

3.66 3.56 2.23 2.30

antique

Thailand

Burma

23 24

oval

Thailand

19

oval

Burma

49

-0.8 40.9 48.0 -19.3 -1.3 44.0 45.8 -21.9

7.

oval

pink-orangy red

2.11

medium

2.07 3.56 1.02 0.98 2.12 3.76

antique antique antique pear

Thailand Thailand Thailand Thailand Thailand

26 24

46.2 2.4 45.9 0.2 -7.2 42.5 38.8 -19.3 50.5 -19.1 12.1 19.6 21.7 -40.7

8.5RP2.5/10.7 7.9RP2. 3/10.6 5.4RP1.7/10.2 0.6RP3. 7/10.3 2.2RP3.6/12.8 9. 1P 2.2/5.1

Corundum Ruby

dark pinkish-red dark red

medium

pinkish-

5RP

2.2/9.5

2.2RP2.3/12.3 7.6RP1.8/10.2 0.6RP4. 8/12.0

red red

violetish-red violet

Sapphire

pinkish-red light pink medium purpleblue

dark green fine

medium dark

oval oval

Sri

Lanka Lanka

antique

Sri

4.25

oval

Sri

5.21

oval

Sri

6.05 2.60 4.02 16.12 1.98

oval

Sri

oval

Sri

oval oval

Sri

antique

Umba

18

38 37 23 38

8.9PB3.7/102

Lanka Lanka

20

-11.6

11.5

21

23.0

-482

7.6PB2.0/12.1

Lanka Lanka Lanka Lanka

47

9.7

17

-30.9 -39.0 -21.8

7.4PB 4.6/7.3 7.0PB 1.6/9.7

37 70 52

15.5 33.7

-0.3 -5.4

56.8 19.8

79

4.7

5.4

34

7.2

-8.9

3.

55

8.3

38.2

0.1Y 5.4/6.0

36

154

12.3

9.

5R

40

44.7

15.6

2.

8R 3.9/10.5

42

84

-19.3

8.7PB4. 1/4.6

55

-9.1

19.2

3.5GY 5.4/2.9

54

5.4

-23.3

30

33.7

35.6

8.2GY 1.9/2.4

blue

medium

blue

dark blue violetish-pink

dark lemon yellow medium green

Sri

Valley,

8. 5P

3.6/8.9 6.9/8.2 9.3Y 5.1/2.7 3. 8Y

Tanzania very pale yellow

1

40

antique

Umba

Valley,

1.0YR 7.8/1.3

Tanzania red-violet

1.86

emerald cut

Umba

Valley,

1P 3.3/2.5

Tanzania orangy-yellow

3.41

antique

Umba

Valley,

Tanzania

brown-pink

3.28

emerald cut

Umba

Valley,

3.5/3.7

Tanzania

o rangy- red

0.96

antique

Umba

Valley,

Tanzania blue-violet

377

antique

Umba

Valley,

Tanzania

green

1.46

round

Umba

Valley,

Tanzania

powder-blue

2.56

round

Umba

Valley,

6.

9PB

5.3/5.5

Tanzania

brownish-orange

4 64

antique

Umba

Valley,

1.1YR 2.9/8.9

Tanzania [continued]

COLOR MEASUREMENT AND SPECIFICATION

30

TABLE

2.

(Continued]

Shape

Gemstone

Color

Weight

Heated Geuda

dark golden yellow

oval

Sri

oval

Sri

dark orange

6.13 3.89 4.00

oval

Sri

yellow

2.21

oval

Sri

orangy-yellow dark blue dark blue-green dark pink dark blue beige-yellow dark blue medium blue medium light blue light blue blue-green light yellow-green light greenish-

3.60 3.87 5.75 6.20

oval

Sri

emerald cut emerald cut

Australia

oval

Lanka Kashmir Sri Lanka Montana Montana Montana Montana Montana Montana Montana

60 28 40 52 77 48

Montana Montana Montana Montana

64 70 58 60

medium orange

Miscellaneous

Lanka Lanka Lanka Lanka Lanka

Australia Sri

—

—

Location

L*a*b* 81

42 53 80 58

11.6 11.2 31.5 8.0 11.4

15 18

-7.1

52 25

5.55 2.30 1.35 1.19 1.40 1.47 1.77 1.66

oval

octagon

orange-mauve

1.10 0.95 0.96

beige

1.03

pear

violet

0.96

orangy-red dark red

1.87

emerald cut emerald cut round emerald cut round round

Mexico Tasmania South Africa

60 33

Turkey New York

Kenya

69 72 36

antique

USSR

10

emerald cut

Tsumeb,

28

pear octagon pear shield

pear pear shield

75 70

.

8.7

25.8 5.0 13.7

Munsell 78.3 54.6 92.3 78.3 70.0 -32.0-7.3

-18 -25.0 1

0.1

1.0Y 7.9/1 1.9

0.7Y 5.7/10.7 5.7PB 1.4/7.8 2.5B 1.7/2.2 7.7P 5.1/7.0

5.4PB 2.4/6.0

29.9

6.

-8.4

4 8

-7.3 -6.0

-135

0.9 2.0

-17.0 -13.5

-8.2 -8.6

-119

0.7 13.3 25.3

-4.0 -2.0

13.3 26.7

5.8 8.1

5.8 9.5

Y 8.0/12.1

0.4Y 4.1/8.4 7.3YR5.2/15.7

0YR 5.9/5.4 0B 2.7/2.5 8B 3.9/3.6

4.8PB 5.1/4.1 7.0PB 7.6/3.1 1.1BG4.7/1.5 6.

1GY

7.4/2.2

4.0GY 6.9/3.8

yellow light

green

yellow

Creedite Crocoite Cuprite

Diaspore Diopside

chrome chrome Dioptase

pale gray-yellow

medium green dark green dark green green

11.62 2.10 2.23 0.75 4.95 0.41

shield shield

6

0.1GY 6.3/1.8 4. 8Y 6.9/3.8 0.6YR 5.7/1.5 1.7YR 5.9/2.2

15.7

-12.6

50.0 48.5

75.0 27 .7

3.0YR3.2/15.8 6.9R 0.9/1 1.1

-0.8 -3.5 -26.2 -18.0 -62.6

13.8 15.6 51.0 35.7

4. 2Y

-1.2

1.5BG

32.5 54.0 40.0 21.7

1.9Y 5.1/4.8 4GY 3.1/7.8 7. 7YR 4.9/6.8 0.1 Y 0.9/3.5 3. 6BG 7.6/0.9 0.8PB 3.4/5.0 0.9G 5.8/5.3 2 OR 6.9/4.4 1.8P 1.6/7.1 4. 5G 4.3/3.6 3.8Y 6.1/7.2 2.2PB 3.5/7.6

6.

6P

5.9/4.4

6.8/2.0

7.

6Y 7.1/2.2

4.

7GY 5GY

3.

3.5/8.0 0.9/5.5 2.7/1 2.0

Namibia Enstatite

brown green light

Epidote Euclase Fluonte

brown

dark brown light blue-green dark blue emerald-green

pink violet

blue-green yellow blue

0.52 2.43 4.38 3.43 1.33 0.24 3.05 0.92 5.75 6.05 8.80 75.77

round pear emerald cut cushion emerald cut emerald cut pear round round

Burma Africa Africa

52 32 50

Africa

2

Brazil

-4.6 0.0 -4.5 -20.4 -27.0 19.1

Switzerland

77 35 59 70

Illinois

17

20.3 -25.1

oval

England

7.6

Illinois

44 62 36

-19.8

round marquise

0.1

49.8 31.3

round round round

Korea Korea

50 47 29

-13.2

USSR USSR

51

-38.8

Asbestos,

44

14.4

Zimbabwe Colombia

Illinois

3.3

-20.2 14.8 7 3

18.4

-2.8

6.8

2.

Garnets Andradite

medium green olive

green

brown Demantoid Grossular

medium green medium orange

0.47 0.51

0.33 0.68 9.81

emerald cut round

East Siberia,

0.3 15.6

33.2 40.3 44.3

2.

5GY

4

2Y 4.6/5.8

8.

9YR

4.9/4.8 2.8/7.4

7.2GY 5.0/9.8

54.6 28.0

5.

9YR

4.3/5.2

Quebec light light

mint green brownish-

4.15

antique triangle

Tanzania Tanzania

70 55

-11.9

5.01

6.3

19.6 32.9

0.1

2.59

emerald cut

Tanzania

84

9.4

38.9

8.

4.48

antique

Tanzania

51

19.6

179

10.0R 5.0/5.0

5.8GY 6.9/3.2 Y 5.4/5.1

yellow light

brownish-

2YR

8.3/6.3

yellow

cinnamon brown

COLOR MEASUREMENT AND SPECIFICATION

Gemstone

Shape

Color

Weight

near colorless medium mint green dark green

2.18 3.88 2.47

dark orange very pale green medium brownish-

4.82 4.14 12.80

antigue antigue

11.39 6.38 8.23 8.56 14.46

antigue

round antigue

emerald cut

Tanzania Tanzania Tanzania

Munsell

L*a*b*

Location

92 58 50

31

Y 9.1/1.3

0.9

8.4

-168 -46.6

23.0 34.6

0.5G4

0.3YR 8.7/14.7

0.1

6

9GY5

7/4 1 9/9.2

(tsavorite)

Malaya

triangle

Tanzania Tanzania Tanzania

88 77 30

44.4

66.0

2.9

4.6

25.6

24.6

Tanzania Tanzania Tanzania Tanzania Tanzania

44 45 39 48 25

17.3 16.9 8.0

30.7

3.

5YR

7.6/0.9

0.6YR 2.9/6.5

orange brownish-pink

orange gray- brown pinkish-orange dark orange

triangle

antigue antigue antigue

19.1

35.9

5.6

206 21.3 48.9

9.1R4 3/1.7 5.3YR 8.0YR 1.3YR 3.3YR

4.4/5.9 3.8/3.5 4.7/5.2 2.4/10.6

Pyrope-

Almandine

medium

Rhodolite

Spessartine

dark

light

violet

orange

medium orange Spessartine

dark orange dark brownishorange dark brownishorange light orange medium brownishorange dark orange very dark brownishorange light orange

1.8

-5.7 38.4 22.0

antigue

12 10 16

3.61 3.81

round round

Orissa, India Orissa, India

18.1 29.1

5.65 4.05

oval

Orissa, India

pear

Brazil

55 45 22 25

emerald cut

Madagascar

4.65

oval

6.41

antigue

1.27

fine

367 -24.8

?

brown-orange brownish brownish-violet

Lanka

Tanzania Tanzania Tanzania

3.09 0.74 0.58

red-violet

round round round round emerald cut

28 54 23 30 26

rose-pink rose-pink dark red light

6.48 10.88 13.10 24.46

15.40

1.27

16.80 1.75

oval

round

Sri

North Carolina Arizona

Mozambigue

33.5 38.1

38.6 22.5 31.7 37.6

8.3RP 2.7/8.5 3.4RP 5.3/6.0

284

1YR 2.2/9.0 5R 2.9/8.9 8. 5R 2.5/9.3

-9.1

2.3RP 1.1/5.7

7.3

2.

6

2.

OR

0.9/7.3

-4.8

6.0RP 1.5/9.0

383

5.

5.2YR4.4/10.6

31.1

55.8 54.2 31.8

14

30.3

41.4

4.1YR 1.3/8.8

Amelia, Virginia

40

?

31

28.3 37.2

37.9 58.6

4.

34.2

4.

9YR

5.4/7.0

7YR2 .1/10.8

1.2YR 2.4/8.0

2.

8YR 1YR

3.9/8.2 3.0/11.9

round

Africa

38

antigue

Brazil

4

27.5 26.5

29.6 26.7

1.2YR 3.7/7.3 2.0YR 0.9/6.7

round

Ramona,

74

34.5

62.4

3.1YR7.3/12.5

40 50 44 32

-49.0 -46.6 -47.2 -51.8

32.4 34.6 27.8 32.6

0.5G 4.9/9.2 1.6G 4.3/8.9

Germany

1.0

-40.0

-6.0

Switzerland

52 25 46 52 35

Italy

51

41.7 52.6 51.5 42.6 67.0

India

28 26 65 50 34 48 40 47 59

California

Tsavorite

medium dark green medium green medium green

4.11

oval

fine

2.47 1.25

emerald cut emerald cut

dark green

4.01

oval

Tanzania Tanzania Tanzania Tanzania

fancy pear

Arizona

Hauyne

blue

Hypersthene

dark bottle green

Idocrase

brown green

brown brown lolite

Kornerupine (chrome)

blue blue light

green

light

brown

Lazulite

olivy-brown medium blue dark blue blue

Microlite

green

Manganotantalite

red yellow

Kyanite

Opal

brown -gray

0.04 2.52 2.30 1.05 3.82 1.40 1.56 3.00 0.40 12.07 2.62 8.30 4.01

0.70 0.14 4.85 11.74 5.15

round round emerald cut cushion round emerald cut round round

Africa

oval

Sri

cushion cushion round

Brazil

oval

Brazil

cushion emerald cut round

Mozambigue

11

37.2

Idaho Mexico

49 35

5.5 0.7

Africa

India

Africa Sri

Lanka Lanka

Brazil Brazil

14.9

-14.4

15.9 6.6 10.7 -24.0 10.1

-25.3

-32.1

28.6 30.5 19.7

5.4

-1.0 -11.6 -21.7 1.0 -33.0 -6.1 -31.5 -24.0 233 36.5 59.3 12.7

1.0G 3.9/9.4

1.1G 3.1/9.8 4.

1PB

5.1/9.7

8.1Y 2.4/5.7

2YR

4.5/8.5

LOGY

5.1/7.1

9.

3YR

3.4/7.2 2.4Y 5.0/9.9 8.2PB 2.7/5.9 8.

7.6PB 2.5/6.1 0.1G 6.4/6.7 0.3Y 4.9/4.6 5. 5Y

3.3/2.8 4.7/5.8 3.8PB 3.9/8.0 1.5PB 4.6/7.8 9. 4GY 5.8/5.1 7.

9B

1.2YR 10/9.4 2.

5Y 4.8/8.7

3.2Y 3.4/1 8 (continued)

'

COLOR MEASUREMENT AND SPECIFICATION

32

TABLE Gemstone

Color o rangy- red light

orange

medium green medium green

Peridot

light light

green green blue-green

Weight

2.

(Continued)

Shape

Location

triangle

Arizona Arizona

4.51

pear

Norway

8.22

oval

Egypt

0.81

emerald cut round

Bolivia

4646 47 34 66 58 85

Germany

18

emerald cut

Brazil

oval

Brazil

57 37

fancy oval

Zambia

oval

Brazil Brazil

6.41

round round

6.38

fancy

0.76 8.04 8.25 9.20

Phosphophyllite

light

Proustite

dark red

2.58

lilac

6.22 9.18 8.52 4.40

round oval

antique

Mexico Mexico

Munsell

L*a*b* 50.9 19.3

-20.9 -11.9 -19.0 -13.3 -4.2 51.6

95.4 55.7 52.3 48.5 31.7 31.9 -1.4 50.0

4.0YR4.5/186 8. 1YR 4.5/9.5 3.2GY4.6/7 7 0.1GY3.3/6 6

9GY 6.5/5.2 0GY 5.7/4.7 9. 8BG 8.4/0.9 5.

3.

10. OR 1.7/13.5

Quartz

Amethyst

light violet

dark

violet

medium dark violet medium dark violet medium dark purple dark purple

3.61

Brazil

6 6 12 14

19.4 -12.0 18.5 -14.5 25.5 -26.0 22.8 -21.1 29.8 -29.0 20.1 -23.2

Brazil

12

25.9

8. 6P

5.6/5.0

7.1P 3.6/5.2 3.0P 0.9/8.0 3.

9P 0.9/6.9

3.3P 1.1/9.2 2.3P 1.3/6.8

-25.3

3.5P 1.1/8.0

30.8 -23.4 13.5 43.1

7.8P 0.9/8.5

emerald cut "Siberian" medium yellow-

Citrine

14.91

7.55

round

Brazil

8.81

oval

Brazil

38 55

7.9 5.4

pale straw-yellow

12.64 16.90 19.72 15.76 15.33

oval

Brazil

61

antique

Brazil

oval

Brazil

oval

Brazil

oval

Brazil

56 53 33 29

0.7 12.1 19.2

34.8 23.9 19.3 61.0 66.5

21.7 30.5

51.1 61.1

oval

Brazil

52

-9.5

emerald cut

Brazil

13.1

13.0 4.2

antique

Brazil

51 71

round emerald cut emerald cut

Brazil

6.0 7.6 4.5 5.6

12.3 23.7 22.5

orange

Green quartz Rose quartz

("Madeira"] apple green medium pink pale pink

Smoky

medium brown

4.48 14.20 18.79 23.78

brown

15.61

light

medium

yellow-

brown dark brown very dark brown pink pink

orangy-red pink red gold-yellow gold-yellow very pale yellow lemon yellow violet

Scheelite

straw yellow

Scorodite

violet-blue violet-blue

Sinhalite

dark straw-yellow

brown green Smithsonite

52

4.20

dark orange dark orange

Scapolite

Brazil

dark straw-yellow

medium orange

Rhodochrosite

Para, Brazil

round

orange brownish-orange

light

quartz

8

oval

yellow pale yellow

beige

9.37

13.57 7.49 11.88 7.15 9.42 3.95 24.60 32.44 32.00 5.77 9.03 4.36 2.85 1.15 1.50 4.58 7.07 4 18 9.18 8.00 10.40

Brazil

26 63 43

emerald cut emerald cut

Brazil

20

antique

Colorado

39

40.2

rhomboid

Peru

51

42.1

round round

South Africa Argentina

30 49

antique

South Africa

16

52.7 37.6 43.6

oval

Tanzania Tanzania Brazil

67 53 76

-1.8

Burma

61

Tanzania Korea

30 84 23

antique antique antique oval

pear fancy pear antique oval oval oval

round oval

Brazil

Brazil

Namibia Namibia Sri Lanka Sri Lanka Sri Lanka Sri Lanka Namibia Namibia

1

15

50 16

47 65 75 73

6.1

8.4YR 5.1/7.1 0.1 9.

Y 3.7/5.4

8YR

5.4/3.8

7Y 6.0/2.8 0.1 Y 5.5/9.5 2.

8.7YR5.2/10.9 7.

4YR

3.2/8.9

6.3YR 2.7/1 6.

5GY

2.

OR

1.3

5.1/2.3

5.0/3.1

0.2YR 7.0/1.5 5.

6YR

0.1 0.1

2.5/2.4

Y 6.2/3.7 Y 4.2/3.5

15.1

6.5YR 1.9/2.8 6.

1.0

11.6 11.4 11.9 52.3 15.6 44.9 55.4 53.7 11.8 37.0

16.1

-16.2

8.6 6.8

3.0 3.2

0.0 5.7 5.3 6.6 16.7 1.0

8.9 4.2 1.3

30.3

-13.4

1

6YR 0.9/2.2 8R 3.8/9.4

1.3R 5.0/9.9 10. OR 2.9/14.0 3.

5R

4.8/8.8

1.2YR 1.5/1 1.4 2.5Y 6.6/8.1 3.

0Y 5.2/7.9

5. 9Y

7.5/1.6

Y 6.0/5.4 4 2P 2.9/5.0 2. 5Y 8.3/4.4 3.1

0PB

2.2/3.3 1.4/6.6 0.1Y 4.9/5.1 8.1YR 1.5/6.5 3. 2Y 4.6/3.7 9. 1YR 6.4/5.9 5.6YR 7.4/1.6 8.

-268 4.9PB 32.5 37.6 25.6 37.0 9.0 6.0

9.3YR 7.2/DQ

COLOR MEASUREMENT AND SPECIFICATION

Gemstone

Weight

Shape

0.85 1.93 3.30 4.65 14.48 5.57 6.22

emerald cut round round round round round emerald cut

Namibia Colorado

emerald green brown

1

round round emerald cut round round round

Baja,

medium green

1.55 1.76 7.01

India

51

antique

India

79

Color

Socialite

intense dark blue

Sphalerite

green yellow-orange dark green dark orange light orange brownish yellowgreen

Sphene

light

light

yellow-green

light

brown

yellow-green yellow

1.01

44

4.22 2.65

Location

Spain

Mexico Spain Spain

Madagascar

Baja,

Mexico Mexico

India Baja, Baja,

Mexico Mexico

Munsell

L*a*b*

23 68 72 43 39 55 49 73 28 34 24 60

200 -43.2 -2.8 6.9 0.6 38.1

33

73.4

100 55.0 86.6

7.7PB2.2/10.8 5.1Y6.7/10.4 2.

7Y 7.1/14.7

4. 6Y

4.2/7.9

26.6

103

6.3YR3.8/15.5 2.9R 5.4/6.3

2.3

66.9

4. 0Y

-10.8

56.2 51.0 47.5 34.2 80.4 67.8 74.9

8.

21.2 17.5

-33.3 11.9

-1.3 -5.8

4.8/9.7

1Y 7.2/7.8

9YR 2. 3GY

2.7/8.9 3.3/6.9 8.5GY 2.3/7.2 0Y 5.9/12.3 1 5. 2Y 5.0/9.6 5. 7Y 7.8/10.5 7.

Spinel

Blues

dark blue medium dark blue blue lavender-blue greenish-blue cobalt-blue light

slightly violetish-

8.35 9.20 9.30 15.22 4.78 11.23 7.27

oval

Sri

oval oval

Sri

oval

Sri

round emerald cut round

Sri

antique

Sri

oval

Sri

antique

Sri

oval

Sri

oval

Sri

antique

Sri

8.21

round

Sri

7.65 5.23 9.02 7.07

oval

Sri

5.89 6.56 8.87 11.40 5.30 2.98

Sri

Sri

Sri

Lanka Lanka Lanka Lanka Lanka Lanka Lanka

12 15 31

50 21

6

29

-0.6 -12.7 -6.9 -127 -6.6 -11.9 4.8 -16.8 -13.6 -11.1 -2.3 -19.7 2.8 -20.8

2.1PB

1.1/3.1

6.2B 1.4/3.3 7. 7.

2B 3.0/3.2 5PB 4.9/3.9

0.7B 2.0/3.8

0.8PB 0.9/4.8 4.

8PB

2.8/5.1

blue

dark

violet

magenta

medium

purple

blue-violet

Pinks

light purple gray-blue dark rose-red light rose-red dark pink

dark violetish-red

medium

reddish-

purple grayish-pink medium pink slightly bluish-pink light dusty-pink

Reds

dark orangy-red

medium

pinkish-

5.46 3.96 11.98 8.53 7.98 14.96

Lanka Lanka Lanka Lanka Lanka Lanka Lanka Lanka

13 19 14

25 27 30 14

-13.7 -4.5 -9.2 7 2 6.0 -12.6 -9.0 14.4 -5.1 -8.5 5.2

44.4

27.0 25.3

2.4

21

19.3

Sri

Lanka Lanka

26

27.1

-0.7 -4.8 -2.2 -6.8

oval

Sri

Lanka

oval

USSR

21.4 41.6

2.0 3.8

oval

Sri

antique

41

15.4 16.2 24.7 43.5

-2.5 -2.8

oval

Burma Burma Burma

47 68 42 54 27

round

Burma

42

34.5

7.8

round

Burma Burma Burma Burma Burma Burma

45 48

26.4 23.6 14 7 36.8 41.5 47.5

14.4

53 59 58 63 65

oval

Burma

oval

Sri

oval

round

Lanka

30 24

-24.8

20.7 10.4

7.2PB 1.2/3.4 6.3RP1.8/106 2.

OP

8.

6PB

1.3/2.5 2.4/3.1 9. OP 2.6/3.7 6 9B 2.9/2.3 9.3RP 1.3/6.3 7. 1RP 2.9/5.8 4. 7RP 2.3/6.0 5. 9RP 2.0/4.6 3. 9RP 2.5/6.6

8.1RP 4.6/4.9

4RP 5RP

6.7/9.7 4.1/3.7 4. 1RP 5.3/3.9 10. OR 2.6/6.0 0.9R 4.0/10.3 7.

4.

orange

medium brownish-

3.07

0.7R 4.1/8.2

pink

medium brown light

brownish-pink

dark grayish-pink dark red

medium medium

red pinkish-

2.34 10.98 3.95 8.89 2.68 3.21

oval

round oval oval

round

31

8

30 27

8.1

4.1

31.8 25.1 7.4

7R 4R OR

4.4/6.2 4.7/5.5 2 3 0/3.4 0.2YR 0.9/9.1 6. 8R 2.9/9.7 0.1R2. 5/11.1 5. 2.

red

Spodumene

blue

medium medium

pink pink yellow-green dark pink

29.85 16.06 17.76

oval

Brazil

emerald cut

Afghanistan

oval

California

17.01

emerald cut

Afghanistan

47.33

oval

Brazil

-3.4 -2.7 -17.7 -12.9 19.1 -10.9 -5.3 28.0 32.2 -19.0

7B 3B

5.2/1.0 5.8/4.8 9.1P 5.7/4.8 7. 5Y 6.2/3.9 8 7P 6.4/8.3 6

2.

(continued)

COLOR MEASUREMENT AND SPECIFICATION

34

TABLE Gemstone

Color

Taaffeite

gray-mauve

Topaz

yellow-brown red-orange dark beige

Weight

yellow

medium

blue

red-orange

medium

pink

[Continued]

Shape

Location

50-

Sri

round emerald cut round

USSR

465 2525

oval

Brazil

38 49 56 59

oval

Brazil

61

8.76 7.20 8.45 17.84

antique

Brazil

63 60 65 73

Lanka

Brazil

Mexico

oval

Brazil

antique

Brazil

oval

USSR

Munsell

L*a*b*

rhomboid

1.60 6.72 12.59 5.29

dark orange brownish-pink

2.

4.5 13.0 38.6 12.0 8.6 23.9 35.0

-14.3

37 2

9.0RP 4.9/1.0 8.6YR 3.7/6.2

37.5

9.

0.8

263 277

9R 4.8/10.1 2YR 5.5/4.8 8. 3YR 5.8/4.6 6.

61.5' 6.6YR6.0/10.8 8. 6RP 6.2/8.2 5.7 -17.6 6.1 B 5.9/5.2 26.8 7.6R 6.4/8.7

34.4 25.2

-169

7.

7P 7.2/6.7

21.2

6.

4R

-0.9

7.6RP2.3/11 9.6RP 0.9/6.5 5.8RP 1.9/9.1 0.1R 1.1/9.1

Tourmaline Rubellite

pinkish-orange dark red-violet very dark violet-red

medium

violet

dark red

36.85 13.16 17.13 16.73 10.26

emerald cut

Madagascar

oval

Brazil

25 24

emerald cut

Brazil

5

38.3 47.8 28.0

antique antique

20

38.1

-5.0

Ouro

12

39.5

7.4

Brazil

Fino,

2.8

2.4/8.9 1

Brazil

Blues and Greens

dark pinkish-red intense smalt blue blue-green fine green

9.

OR 1.8/9.7 6GY 4.0/4.3

2.

3BG

emerald cut emerald cut emerald cut

Brazil

19

41.8

Brazil

41

-21.0

Brazil

Africa

50 30

-40.1

triangle

-30.7

10.4 18.8 -0.1 23.9

968

emerald cut

Brazil

52

-39.7

15.9

3.9G 5.1/7.3

14.75 10.90 5.74

emerald cut round

Brazil

-38.8

31.1

31.1

Tanzania

18.6

20.5 56.6

0.1G3.1/7.7 7.2R 4.1/7.4

antique

32 42 43

round

Tanzania

48

20.9

70.4

8.7YR4.7/11.6

10.39

oval

Tanzania

28

10.7

46.0

0.4Y 2.7/7.1

46.84

oval

Tanzania

31

24.0

26.4

1.8YR 3.0/6.4

32.32 10.95

oval

Afghanistan Brazil

57 28

34.7 34.0

0.0

round

-4.2

6.5RP 5.6/8.2 5.6RP 2.7/8.1

11.13

antique

Mozambique

44

28.7

12.5

4.

21.22

emerald cut

Stewart Mine,

38

187

20.6

1.7YR 3.7/5.0

36.56 9.84 15.96 10.05

2.

4.9/7.7

0.1G 2.9/6.0

(chrome) slightly yellowish-

Orangy Colors

green dark green peachy-orange medium brownishorange dark brownish-

4.84

Mozambique

8.

5YR

4.2/9.4

orange

medium orangybrown

medium

pinkish-

brown Pinks

medium pink medium dark

rose-

pink slightly

brownish-

1R 4.3/6.6

pink

brown-pink

Pala,

California

Mozambique

medium

Color Suite

beige light pinkish-beige near colorless light pink dark rose-pink dark green dark brownish-

pinkish-

2.51

round

Mozambique

66

23.7

7.7

1.4R 6.5/5.6

2.37 2.59 2.19 2 15 2.16 2.34

round round round round round round

Mozambique Mozambique Mozambique Mozambique Mozambique Mozambique

78 85 56 35 24 34

19.1

5.5 3.9

0.4R 7.7/5.6 3.5R 8.4/1.9

round round round round round round round round

Mozambique Mozambique Mozambique Mozambique Mozambique Mozambique Mozambique Mozambique

52 64 69 84 87 37 36 45

7.9

-5.7 33.2 47.0 -11.6 -12.8 22.0 -14.7 37.0

4.

1RP

5.5/8.0

3.9RP3.4/11

6GY 2. 4GY

4.

.5

2.3/3/5 3.3/5.4

green

medium green

brown

2.68 2.10 3.08 2.22 2.04 2.33

dark brown

1.81

blue

2.30

lime green very pale green colorless beige-yellow light

-8.3 -8.6 0.1

41.4 26.0 12.8

1.5

2.1

3.8 9.0 18.9

21.6 51.1

-8.4

-2.1

33.8

8. 5Y

5.1/5.7

1.2GY 6.3/3.7 2.9Y 6.8/1.8

3YR 3YR

8.3/0.4 8.6/3.4 1.2Y 3.6/7.8 5. 6YR 3.5/6.4 6.2BG 4.4/1.7 2.

9.

COLOR MEASUREMENT AND SPECIFICATION

Gemstone Willemite

Color golden yellow

Weight 2.35

Shape pear

Franklin,

New

Munsell

L*a*b*

Location

85

35

2Y 8.4/8.9

63.0

6.

1.0

290

2.8Y 6.2/4.2

43.8

96.1

5.4YR4.4/17.6

-

7.4

Jersey Wulfenite

yellow

6.11

oval

orangy-red

2.54

emerald cut

Namibia Red Cloud

63 45

Mine, Arizona

Zircon

reddish-brown brownish-yellow

19.03 17.43

violet-rose

dark orange green rose-red lemon yellow medium blue yellow pale gray-green

reddish-brown light olive green dark blue light

pink

orange medium orange light

pale blue-green Zoisite

violet-blue light

blue-gray blue

medium

violet-blue

brown-blue

oval

Sri

oval

Sri

1420

round

Sri

9.26 4.36 11.26 15.70 5.56 8.92 16.63 7.77 5.34 2.87 1.36

oval

Sri

1.44

2.59 2.67 26.54 1.06 2.30 0.96 0.92

Lanka Lanka Lanka Lanka Lanka Lanka Lanka

oval

Sri

emerald cut

Sri

oval

Sri

oval

Cambodia

oval

Sri

antique

Sri

oval

Sri

round round round round round round pear round round emerald cut emerald cut

Sri

Lanka Lanka Lanka Lanka

Cambodia Sri Sri Sri

Lanka Lanka Lanka

Cambodia Tanzania Tanzania Tanzania Tanzania Tanzania

17

37 20 33

48 19

50 46 65 55 26 47 56 71

59 52 77 20 75 60 47 61

16.2 12.2 30.9 25.5 15.4 26.2

-0.3

-123 10.8 7.8 23.0

16.7

2.2YR

496 34

0.1Y 3.6/7.8

66.0 25.8 8.3

31.6 -14.1

-6.9 55.0 0.7 3.5

9.4RP 1.9/7.2 7.9YR 3.2/1 1.4 5.4GY 4.7/4.2 3.1R 1.8/5.9 4. 2Y

4.9/4.5

4.9B 4.5/4.2

Y 6.4/9.0

58.1

0.1

14.6 29.1 19.2

5.4/2.7 2.5/6.5 4. 3Y 4.6/2.7 6 8B 5.5/3.3 0.7B 7.0/2.8

58.1

5.7YR5.8/10.6 4.0YR5.1/13.9

-0.3 -8.4 -11.1 -5.8 -11.9 26.2 39.4

1.6/4.1

70.9 -1.4 -76.3 0.6

-20.7 16.8 -35.7 -11.7 7.1

4YR 3. 2YR

5.

7.2BG 7.6/1.4 8.6PB 1.9/20.9 9.5R 7.4/0.1 6.

4PB

5.9/4.8

8.8PB 4.6/8.7 2.

OP 6.0/3.0

A ACHROITE ACTINOLITE

See

1.619-1.622;

/J

=

1.632-1.634; y

=

V=

also: Tremolite; Nephrite; Pargasite.

0.022-0.026.

Birefringence:

2

Pleochroism:

Crystallography: Monoclinic; bladed crystals, usually granular. Often twinned.

a: pale yellow/yellowish-green. /J:

Pale to dark green, blackish green, black.

Colors:

Yellow to dark green. Material transpar-

ent to nearly opaque.

elongated; fibrous, columnar aggregates. Also massive,

pale yellow-green/green.

y: pale

green/deep greenish blue.

Vitreous, sometimes dull.

Luster:

Faint line at 5030.

Spectral:

Hardness: Density:

5.5

Luminescence:

Usually 3.05; Tanzania: 3.03-3.07; Max.: 3.44.

Cleavage: tle.

=

1.642-1.644 (Tanzanian material). See diagram on p. 38. 78°. Biaxial (-); 2

Ca (Mg, FehSigCMOH^

Formula:

a

Optics:

See: Tourmaline.

Occurrence:

2 directions good, often fibrous nature. Brit-

Compact

None (due

to presence of Fe).

Contact metamorphic limestones and dolo-

mites; magnesium-rich limestones

variety tough.

regionally

metamorphosed

and ultrabasic rocks;

rocks.

Tremolite-Actinolite Data Birefrin-

Locality Fowler,

New

York

Kenya Tanzania (Lelatema) Tanzania Tanzania (Merelani)

Taiwan

Pleochroic Colors red-violet

bright green

P

y

gence

1.602 1.602 1.607

1.630 1.628 1.632

0.028 0.026 0.025

3.03

Hexagonite

1.613 1.618

299

Tremolite

1.631

0.023 0.028 0.022

3.01

1.6301.633

0.023-

3.01

Tremolite

—

1.6311.633

0.0140.016

301

Catseye tremolite

1.6321.634

1.6421.644

0.021-

3.043.07

Tremolite-Actinolite

0024

1.653

0.020

3.15

Actinolite

yellow green/green

1.608

emerald green

1.611

yellow-green/emerald green yellow-green/green tones, also brownish

1.608

1.616 1.623 1.618

—

1.6071.609 1.6151.619

Uganda

yellow-green/green

green/brown

Comments

a

1.6191.622

-

1.633

37

1.639 1.630

S.G.

3.01

3.30

Tremolite Tremolite + Cr

Smaragdite

0024

ADAMITE

38

Hardness:

1.74

1

Vitreous.

Luster:

R.I.

4.32-4.68 (red-violet).

Density:

72

3.5

Good

Cleavage:

1.70

7

1

direction. Fracture subconchoidal to

uneven.

.

1.68

Optics: D

1.66

Birefrin-

a 1

64

—^ ---

Locality

a

P

y

gence

Mexico (reddish) Mexico (rose) Mexico (violet) Mexico (green) Tsumeb, Namibia (Cu) Tsumeb, Namibia (Co) Laurium, Greece

1.712 1.710 1.710 1.722 1.742 1.722 1.708

1.736 1.735 1.735 1.742 1.768 1.738 1.734

1.760 1.759 1.758 1.763 1.773

0048 0049

1.761

0.039

1.758

0050

35

.

1

62

33

D 1.60 -

3

—"

100

80

90

70 100 Mg

Chemical composition

60

40

50

iMg

+

30

Fe* 2 + Fe* 3

vs. optics

+

20

1

10

Mn)

and density

of

common

Mapimi, Mapimi, Mapimi, Mapimi,

0.048 0.041 0.031

hornblendes.

2V =

+ );

15° (Cu

Adapted from W. A. Deere, R. A. Howie, and J. Zussman, 1962, The Rock Forming Minerals, vol. 2 (New York:

Biaxial

Wiley), p. 296.

in optical properties.

(

Large variations

Dispersion: Chester, Vermont. Madagascar: small, dark green crystals. Many of these are clean and suitable for faceting.

Tanzania: transparent crystals.

in

var.) to

88°.

composition lead to wide variations

Strong.

Pleochroism: Colorless/blue-green/yellow-green. Pale rose/pale rose/pale purple.

Pink/pale rose/colorless.

(See also localities for nephrite.)

and usually in small fragments. Material from Chester, Vermont, could provide stones to about 10 carats. Stone Sizes:

DG:

Actinolite

is

2.06 (greenish, step cut, Africa).

Comments:

Actinolite

is

a

member

Mg end, and

ferroactinolite the

actinolite in the middle. Actinolites with

Fe are very 1.63);

Fe end, with

more than 50%

Catseye actinolite exists (S.G.

rare.

when chatoyant

material

is

cut,

it

is easy to cleave and hard would make a poor jewelry stone. Actinolite

constituent of nephrite (jade). Smaragdite

Name:

3.0, R.I.

exhibits a fine

eye. Actinolite

rich tremolite

to cut

and

is

the chief

a

chrome-

is

from Tanzania.

Greek

aktis,

meaning

Luminescence: yellow in SW. Occurrence:

of a series that

contains varying amounts of iron and magnesium. Tremolite is the

Not diagnostic.

Spectral:

rarely facetable

due

to the fibrous

Secondary mineral

LW;

in the

also

lemon

oxidized zone

of ore deposits.

Utah (various

localities): California:

Nevada.

Laurium, Greece: often containing copper,

in lovely

blue

and green shades. Mapimi, Mexico: fine sprays of crystals in limonite matrix, from the Ojuela Mine. Tsumeb, Namibia: fine crystals, sometimes colored purple by cobalt.

Cap Garonne, France. Also Chile,

ray,

Intense green in SW,

Stone Sizes:

Italy,

Germany, Turkey, Algeria.

Violet crystals noted up to

1

cm

long and

nature.

transparent, would yield stones up to about 1-2 carats.

ADAMITE

Green material usually not clean, would provide only small faceted gems (1-3 carats).

Zn (As04>OH + Co, Cu.

Formula:

2

Crystallography:

Orthorhombic; crystals elongated or

equant; druses, radial aggregates, and spheroids on matrix.

Colors:

Colorless, pale green, yellowish green, yellow

PC: 4.38

Comments:

fragile for jewelry; strictly a collector item.

Name:

and

who

shades (color zoned, contains Co).

Exceedingly rare as a cut gem, although many localities. Much too soft and

the mineral occurs in

(various shades), bluish green, green (contains Cu); rose violet

(pink, Mexico).

After Mr. Gilbert

supplied the

first

Adam,

mineralogist, of Paris,

specimens for study.

AMBER ADULARIA

See: Feldspar.

AGALMATOLITE

See: Pyrophyllite.

ALMANDINE

See: Garnet.

AMAZONITE

See: Feldspar.

AMBER

AGATE

Also: Succinite.

See: Quartz.

ALABASTER ALBITE

See: Calcite,

Formula: Approximately GoH^O + H 2 S. A mixture of hydrocarbons, plus resins, succinic acid, and oils. Amber is the hardened resin of pine trees, sp. Pinus

Gypsum.

See: Feldspar.

-30

succinifera, age

ALGODONITE

Also: Domeykite, Mohawkite.

Cu As (Domeykite =

Formula:

ft

Crystallography:

CibAs).

Hexagonal crystals rare; usually masDomeykite is isometric.

Silver white to steel gray; tarnishes rapidly to a

Colors:

Yellow, brown, whitish yellow, reddish,

Colors: color,

million years.

Amorphous.

Crystallography:

sive, granular, reniforn.

dull

orange shades. Rarely blue, greenish, Greasy.

Luster:

Hardness:

2-2.5.

1.05-1.096 (usually -1.08).

Density: Metallic; opaque.

None. Fracture conchoidal.

Cleavage: 3-4 (Domeykite: 3-3.5).

Hardness:

R.I. -1.54.

Optics: 8.38 (Domeykite: 7.92-8.10).

Density:

Not diagnostic.

Spectral:

Cleavage:

None. Fracture uneven

conchoidal

in algodonite.

in

domeykite, sub-

Luminescence: Yellow greenish in LW. Baltic

Occurrence:

Localities that

produce copper arsenide

minerals.

Mohawkite

is

a mixture of algodonite and other copper

arsenides, from the

Mohawk

Mine,

Keweenaw

Penin-

Michigan.

Domeykite Superior

is

from the

district,

Mohawk

Mine, Michigan; Lake

Ontario, Canada; Guererro, Mexico;

from Chile, Germany, Sweden, and from Cornwall, at Beloves, Czechoslovakia, and Mesanki, Iran. also

England. Related minerals are found

Stone Sizes:

Cabochons could be cut

depending on the

to almost any

availability of large

masses of

metallic rough.

Comments:

Cabochons

of these arsenides are bright,

and metallic and are both attractive and unusual. However, they tarnish rather quickly and the surfaces turn a drab brown and lose their luster. Cut stones are silvery,

rarely seen even in collections, although they are strikingly

beautiful

when

cut and polished to a high luster.

They

must be sprayed with lacquer to prevent tarnishing. Algodonite and domeykite are heat sensitive, and care must be exercised in cutting.

Name:

in

SW.

After the Algodones Mines, Coquimbo, Chile.

amber

See: Epidote.

SW

(Texas); bluish white or

fluoresce grayish blue

is

noted for

its

fluorescence.

Occurrence: In sedimentary deposits and on shorelines, due to the action of waves and currents in bringing material up from offshore beds. East Prussia (now U.S.S.R.): Succinite Entire Baltic Sea region, including Poland, East Germany, Norway, Denmark; also Rumania and Sicily. Sicilian material may be opalescent blue or green. Rarely found in England. Southern Mexico (Chiapas) produces golden yellow material. Burma: brownish yellow and brown amber; also colorless, pale yellow, and orange. Lebanon: scarce, from very old deposits. Dominican Republic: mined from sedimentary rocks, yellow, orange, and red colors; this amber often contains well-preserved insects and sometimes displays a strong bluish tone in reflected light.

Cedar Lake, Manitoba. Canada. Point Barrow, Alaska.

Stone Sizes: The normal size of amber fragments is less than half a pound, but pieces weighing several pounds have been found. Amber is used often in making pipestems, as beads (tumble polished or faceted), pendants, earrings,

and

rings.

It is

also carved,

sometimes ornately;

used as inlay material, umbrella handles, and so forth. Inclusions:

ALLANITE

in

amber may

Inert in X-rays.

Sicilian

Algodonite from Painsdale. Michigan, in fine crystals. In masses from the Algodones Mines, Coquimbo, Chile, and Cerro de Los Aeguas, Rancagua, Chile.

size,

cream

violetish.

brown.

Luster:

sula,

39

Amber is noted for its inclusions, which are

chiefly insects

and pollen as well as leaves and other

.

AMBLYGONITE

40

organic debris. These were trapped that

oozed from pine

in the sticky fluid

trees millions of years

provide an intimate look

at plant

and insect

Vitreous to greasy; pearly on cleavages.

Luster:

ago and

life

of that

Hardness:

5.5-6.

time period.

Approximately 2.98-3. amblygonite = 3.11; montebrasite Density:

Amber is classed in various types:

Comments: (found

in the sea), pit

amber (dug

sea

amber

up, especially from the

1

=

brasite

1

=

2.98;

natromonte-

3.04-3.1.

Baltic area), clear, massive, fancy, cloudy, frothy, fatty,

and bone amber.

Cleavage:

Perfect

1

direction,

good

1

direction.

Optics:

Birefrin-

Species

Locality

a

P

y

gence

Density

1.598 1.612 1.616 1.633 1.615

.020

3.101

.021

3065

.022 .022

3.085

.021

3.04

Amblygonite Amblygonite

Chursdorf,

Germany Sweden

1.578

—

Uto,

1.591

1.605

Montebrasite Montebrasite Natromontebrasite

Karibib,

Namibia

1.594

1

Kimito, Finland

1.611

Fremont County, Colorado

1.594

Frequently seen in amber are flattened starburst

known as sun spangles. These are internal feathand are caused by stress. Amber softens at about 1 50°C and melts at 250-300°C. Pressed amber, or ambroid, is made by melting small pieces of amber together under

shapes ers

great pressure. This

is

608

1.619 1.603

300

Note that refractive indices and optic angle decrease as Na and F content increase. Montebrasite is optically + and amblygonite is (— ). The change in optic sign (where 2V= 90°) occurs at -60% (OH). There appears to be a complete series of (OH, F) substitutions. (

)

None.

Pleochroism:

usually detectable by careful micro-

Amber often darkens with age to a red-brown color. Pressed amber, however, may turn white with age. scopic investigation.

Not diagnostic.

Spectral:

fine

Copal

is

a fossil resin of

more recent

origin than true

amber. Principal localities are South America, Africa, and New Zealand. Copals fluorescence whiter in S W-UV than amber and are easier to dissolve

in solvents.

Optical

and physical properties are otherwise similar to amber. "Kauri Gum" is a copal from the kauri pine tree of New

Amber centuries,

Good

is

in great

demand

more unusual colored

quality material

is

it has been for extremely rare, as

today, as

and very large material

is

for anything but

brown

LW

in

Inclusions:

clouds

(Keystone, South

(Pala, California).

Commonly

in parallel

veil-type inclusions, usually

bands.

Granite pegmatites.

Brazil: origin of ses, fine

SW

or bright green in LW, or pale

most gem material,

in crystals

and mas-

yellow color.

Custer County, South Dakota: masses up to 200 tons at Tinton, South Dakota, in masses.

(nongem) and

Name:

Arabic anbar, which the Spanish converted to ambar, then later to amber. Succinite is from succinum, the Latin

word

for

AMBLYGONITE

amber, meaning juice. Also: Montebrasite

Natromontebrasite (Na exceeds

Formula:

(Li,

(OH exceeds F);

Li).

Na)Al(P0 4 )(F, OH).

Usually Li greatly exceeds Na. Crystallography:

Triclinic; crystals

matic, rough faces. Twinning

equant to short

common.

Usually

pris-

in cleav-

able masses.

ish, tan,

Weak orange

varieties (blue, green).

seldom used

jewelry.

Colors:

Pale blue in

Dakota).

Occurrence:

Zealand.

are the

Luminescence:

Colorless, white, grayish white, yellow, pinkgreenish, bluish.

Also from Arizona: New Mexico: New Hampshire; Pala, California; and Newry, Maine, in crystals up to more than inches. These were found in 1940-41; they

3x4

were heavily included and provided only small gems. Germany; Varutrask, Sweden. Montebras, France: Montebrasite. Karibib, Namibia: Montebrasite. Sakangyi, Burma. Stone Sizes: The largest cut amblygonite is ~70 carats, cut from Brazilian material. The normal size is 1-15 carats. Facetable material is known from Maine, Brazil, and Burma, but cut gems over 10 carats are scarce. SI: 62.5 (yellow, Brazil), 19.7 (yellow, Burma).

,

ANATASE

ROM: 15.6. AMNH: 3 (colorless, DG:

47 (yellow,

Stone Sizes: Gems are nearly always colorless and less than 1-2 carats when faceted. Large crystals from Mt. Ste. Hilaire are white but may have small facetable areas.

Maine).

Brazil).

Gems

Comments:

are highly prized

are usually pale straw yellow and

the color

if

is

darker. Large stones have

been cut but are extremely rare. Amblygonite is too soft and cleavable to make a good ringstone. The material from Karibib, Namibia, is lilac in color and quite beautiful

when

faceted, as well as being extremely rare.

should be noted that reported

in

many

(

+ and

are there-

)

Many gems in collections prob-

ably should be reexamined and relabeled,

Most yellow gems

It

of the so-called amblygonites

the literature are optically

fore really montebrasites.

in collections

if

necessary.

and on the market are

amblygonites from Brazil; however, stones from Mogi das Cruzes, Sao Paulo, Brazil, are montebrasite.

Names:

Amblygonite

is

41

from the Greek words

for blunt

and angle, in allusion to the shapes of crystals. Montebrasite is from the French locality where found.

Crystals in basaltic cavities in general

inch

do not exceed U l

and are transparent.

in size

Comments:

Large colorless crystals of analcime are a

great rarity although small transparent crystals are abun-

gems

dant. Faceted

even

are extremely rare and seldom seen

in large collections.

The hardness

is

marginal for

wear, but the mineral has no cleavage and should present

no

difficulties in cutting.

Name: of the is

From the Greek analkis, meaning weak, because weak electric charge analcime develops when it

rubbed.

ANATASE

Also called Octahedrite. See: Brookite,

Rutile.

Ti0

Formula:

2

.

Tetragonal; crystals pyramidal,

Crystallography:

AMETHYST

See: Quartz.

ated; also tabular

AMMOLITE

See: Korite.

Colors:

stri-

and prismatic.

Black, red-brown, brown, deep indigo-blue;

colorless to grayish, greenish, blue-green, lavender. Band-

ANALCIME

Zeolite Group. See also: Pollucite.

NaAlSi 2

Formula:

6

•

H

2

;

common

usually trapezohedra. Massive, granular. Colorless, white, gray, yellowish, pink, greenish.

Luster:

Vitreous.

Density:

to zonal

growth often

visible.

Adamantine, sometimes

Hardness:

slightly metallic.

5.5-6.

Density:

Colors:

Hardness:

due

Luster:

0.

Isometric good crystals are

Crystallography:

ing

3.82-3.97.

Perfect 2 directions. Fracture subconchoidal.

Cleavage: Brittle.

0.046-0.067.

Birefringence:

5-5.5.

Optics:

2.22-2.29.

o

=

2.534-2.564; e

=

2.488-2.497.

Refractive indices are extremely variable, depending on

Cleavage:

Indistinct. Fracture subconchoidal. Brittle.

Anomalous

Birefringence: Optics:

Isotropic; TV

=

in

temperature and wavelength.

Anatase

polarized light.

is

sometimes

1.479-1.493.

0.213

Dispersion:

Pleochroism: Spectral:

(o);

0.259

(e).

None.

Pleochroism:

Not diagnostic.

Strong

in

deeply colored crystals:

brown/yellow-brown/greenish-blue.

Cream white

Luminescence: Occurrence:

biaxial with small 2 V( dark-colored

crystals).

in

LW (Golden, Colorado).

Secondary mineral

in basic

igneous rocks;

Not diagnostic.

Spectral:

Luminescence:

None.

and sandstones. Washington, Oregon, and California (Columbia Plateau

Occurrence:

area).

rocks; as detrital grains, as an accessory mineral in gran-

also in sedimentary rocks such as siltstones

and

Gneisses, schists, and other metamorphic

Houghton County, Michigan.

ites,

New Jersey: Watchung

Gunnison County, Colorado: Arkansas; Massachusetts; Virginia; North Carolina. Canada; Brazil; Cornwall, England; Wales; Norway; France; Italy; USSR. Switzerland: gem material from the Alpine regions.

India:

Nova

Deccan Plateau. Bay of Fundy

Scotia:

area.

Quebec, Canada. Also Scotland, Ireland, Iceland, Norway, slovakia, Germany, Australia. Mt.

in various

other igneous rocks.

California;

basalt flows.

Ste. Hilaire,

Italy,

Czecho-

Brazil:

found

in

diamondiferous gravels.

ANDALUSITE

42

Faceted gems are exceedingly rare and

Stone Sizes:

always very small material

known

than 1-2 carats). Usually the

(less

very dark and unappealing. Cut

is

~6

as large as

gems

are

carats.

Comments:

Anatase is usually found in very small crysseldom transparent, and even then very dark-colored. Gems have been cut as curiosities, but are almost never seen for sale on the market because of scarcity. tals,

Name:

Greek

meaning erection because the

anatasis,

Metamorphic

Occurrence:

developed within mica Also as a detrital mineral and very rarely in pegmatites and granites. California; South Dakota (Black Hills); Colorado; New Mexico; Pennsylvania; Maine; Massachusetts. East Africa; Spain. schist or gneiss.

main gem source today; found as pebbles in stream beds or on hillsides under layers of clay. Sri Lanka: gem material found as waterworn pebbles, Brazil:

really a tetragonal bipyramid and elongated with respect to the octahedron of the

sometimes large size. Burma: dull green material

isometric system.

Belgium: blue

"octahedron" of anatase

is

rocks, usually slates and

schists as a contact mineral, or

in

gem

gravels.

crystals.

Gems from Brazil reach 75-100 carats. Usually gems are 1-5 carats; stones in the 5-10 carat

Stone Sizes:

ANDALUSITE

Varieties: Chiastolite, Viridine. See:

Kyanite, Sillimanite.

range are available at several times the cost of the smaller

AbSiOs + Fe.

Formula:

ones. Stones over 10 carats are quite rare and extremely

Orthorhombic. Crystals prismatic, stricross section. Massive, compact.

Crystallography: ated, square in

Pinkish, reddish-brown, rose-red, whitish, grayish,

Colors:

yellowish, violet, greenish. Chiastolite: gray crystals with black,

carbonaceous cru-

rare over 20 carats. SI: 28.3 (brown, Brazil), 13.5 (green/brown, Brazil).

ROM:

12.44 (Brazil).

Comments:

Andalusite

is

required

of andalusite

ciform pattern

in interior.

6.5-7.5.

3.13-3.17.

Cleavage:

Distinct

1

direction. Fracture even to sub-

a=

The

1.629-1.640;/?= 1.633-1.644;

y=

1.638-1.650.

Near-colorless andalusite reported at low end of this range; green material at upper end.

(-),2V=

Birefringence:

Dispersion:

73-86°.

0.007-0.011. (Viridine: 0.029.)

mechanism.

Names:

Deep green

from Brazil display

varieties

faint lines at 5180, 4950,

Veil inclusions are

at

Mn

5505

and 4550.

common. Carbon

None

more or

less as a curiosity, since

it is

first noted locality, Andalusia (Spain ). from the Greek chiastos. arranged diagonally, because the pattern of carbon inclusions resembles the Greek letter Chi, which is written x-

SW

(

is

ANDESINE

See: Feldspar.

ANDRADITE

LW. Brown fluorescence in Dark green or yellowbrown-green gems from Brazil).

in

(Lancaster, Massachusetts). in

cut

See: Garnet

inclu-

sions in chiastolite. Hematite flakes in Brazilian material.

green fluorescence

is

After the

Chiastolite

spectrum: knife-edge shadow at 5535, fine lines

SW

material from Ottre, Western Belgium, +2 +3 -Fe charge transfer

andalusite.

Strongly pleochroic; olive green to flesh-

Luminescence:

in

has been attributed to an Fe

a lower hardness and density than other varieties of

Blue andalusite from Belgium: blue/colorless/colorless.

Inclusions:

a deep green variety containing manganese.

black cross on a gray background are quite attractive. it contains, has

Usually yellow/green/red.

and 5475;

the

Chiastolite, because of the impurities

red (Brazil).

Spectral:

is

blue color

Chiastolite

0.016.

Pleochroism:

how

always opaque; cross sections showing a well-formed

Viridine: 1.66-1.69. Biaxial

distinctive

rough was oriented before cutting. Catseye andalusites can be cut when fibrous inclusions are present but are extremely rare. Viridine

conchoidal. Brittle. Optics:

a slightly brittle material and

set as a ringstone.

or various other combinations, depending on

Hardness: Density:

is

if it is

shades; others display green in the center with brown tips

Vitreous to subvitreous.

Luster:

is

The pleochroism and extremely attractive. Sometimes gems are cut to show the pink and almost colorless

care

ANGEL STONE

See: Palygorskite.

ANGLESITE Formula:

PbS0 4

.

ANHYDRITE Orthorhombic. Crystals usually tabu-

Crystallography: lar,

prismatic; granular; massive; stalactitic.

lemon to golden and bluish shades.

43

is required in cutting, and wear is not recommended. Cut anglesites are true rarities and seldom seen except in very complete collections.

cleavage indicate great care

Colorless, white, yellowish gray,

Colors:

yellow, brownish orange, pale green,

Adamantine

Luster:

Hardness: Density:

to vitreous.

Name:

Anglesey, the English locality where

CaS0

Formula:

4.

6.30-6.39; usually 6.38.

Orthorhombic. Crystals equant, thick,

Crystallography:

Good a=

Optics:

1

direction. Fracture conchoidal. Brittle.

1.877;

=

1.883;

y=

Birefringence:

tabular or (rarely) prismatic; massive, cleavable.

Colors:

1.894.

2V -75°.

Biaxial (+),

found.

ANHYDRITE

2.5-3.

Cleavage:

first

Colorless, white-gray, bluish, violet, pinkish,

reddish, brownish.

0.017.

Greasy; pearly on cleavage; vitreous

Luster:

in

mas-

sive varieties.

Dispersion:

0.044.

Pleochroism: Spectral:

Hardness:

None.

Density:

Not diagnostic.

Weak

Luminescence: and LW.

SW

yellowish fluorescence in

Secondary mineral in lead deposits, formed by oxidation of galena (PbS). There are many localities,

and many have the potential of yielding

gemmy

crystals.

2.9-2.98.

Cleavage: Optics:

Occurrence:

3-3.5.

Perfect

a =

1

1.570;

direction, nearly perfect /?

Birefringence:

Dispersion:

Chihuahua, Mexico; England; Scotland; Wales; USSR;

Germany; Sardinia; Broken

Spectral:

In violet crystals: colorless-pale yellow/

Not diagnostic.

Dundas, Tasmania. crystals

from

Touissit, in

immense

sizes

for the species.

Tsumeb, Namibia: large transparent yellowish sometimes colorless, gemmy. Tunisia:

gemmy

crystals,

Stone Sizes: The usual range is 1-6 carats for faceted gems. Anglesites very rarely are large enough to cut bigger stones than this, but some rough has yielded 100+

DG:

88.75 (yellow, coffin-shaped triangle,

A

Tsumeb,

ROM: 23.62 (colorless, step cut, Tsumeb). NMC: 25.90 (yellow, scissors-cut, Morocco). 73

(light

golden brown, Morocco).

(yellow-orange, cushion cut, Morocco).

(lemon yellow emerald cut, Morocco). 171.12 (medium orange, Morocco). 169 (oval, Morocco). 63

Comments:

A

halite,

in

LW

(Germany).

rock-forming mineral, associated with

and limestones. Also occurs in in basalts, and other traprocks. Mexico, New Jersey Texas.

Nova

New

Scotia.

Trance. India,

Germany

Austria, Poland.

Faraday Mine, Bancroft, Ontario, Canada: large purplish masses,

some

facetable.

Simplon Tunnel, Switzerland: pale purple cleavages, facetable.

Mexico: large blue masses, very lovely

Namibia).

PC: 126

Occurrence:

gypsum beds, South Dakota,

from Tsumeb {note: 300-carat stone broke during cutting!) and Morocco.

Red color

Luminescence:

hydrothermal veins, cavities

crystals.

carat gems, notably the material

1.614.

0.013.

pale violet-rose/violet.

Morocco: gem

y =

0.044.

Pleochroism:

N.S.W., Australia;

1.575;

direction.

2V -43°.

Biaxial (+),

Chester County, Pennsylvania; Tintic, Utah; Arizona; New Mexico; Coeur d'Alene district, Idaho. Hill,

=

1

Anglesite gems are colorless to pale brown and are available from only a few localities. The dispersion is equal to that of diamond, and properly faceted gems are truly magnificent and bright. Low hardness and

color.

Volpino, Italy: a white-gray, marblelike textured material

known as vulpinite and locally used made into cabochons.

as a decorative

stone and

Stone Sizes: small

(

Faceted gems are quite unusual, usually

1-5 carats), but potentially

to 9 carats

much

larger.

Gems up

have been cut, but cleavage masses could

provide larger rough. Faceted gems are usually purplish or pale pink, from the Swiss and Canadian localities.

PC:

2.86 (pink-blue bicolor, Bancroft).

Comments:

The

blue or violet color disappears on

heating and can be restored by

gamma ray bombardment.

ANKERITE

44

The

natural color

may

Gemstones

radiation.

therefore be caused by natural

are very fragile

due

Hardness:

cleavages and must be cut and handled with great care.

Name:

Greek without

Vitreous

Luster:

to excellent

ANORTHITE

Optics:

varieties 3-4).

3.10-3.35 (massive varieties 2.5-2.9).

Density: water, in allusion to composition.

See: Dolomite.

(some massive

5

Cleavage:

ANKERITE

in crystals.

Poor. Fracture conchoidal to uneven. Brittle.

e

=

1

.598- 1 .666; o

=

1

.603- 1 .667. Very variable

with composition. See: Feldspar

Gem

varieties: o

=

1.632-1.649, e

Uniaxial (-); francolite

ANORTHOCLASE

=

1.628-1.642.

biaxial,

2V =

25-40°.

See: Feldspar.

Birefringence:

ANTIGORITE

may be

0.001-0.013.

Chlorapatites have the lowest birefringence (~0.001);

See: Serpentine.

medium (0.004); hydroxylapatites higher carbonate apatites as high as 0.008; and francolite

fluorapatites

APACHE TEARS

(0.007);

See: Obsidian.

as high as 0.013.

APATITE

Group name. Also

Formula:

Ca (P0 4 )3(F, OH, Cl) 3 Sr, Mn.

Ca

called Asparagus Stone.

5

Dispersion:

0.013.

Pleochroism:

.

Distinct in blue-green varieties; other-

wise weak. Yellow stones

often replaced by

Also contains: Ce, rare earths, U, Th. P0 4 replaced by SO4 + Si0 2 Carbonate apatites contain CO2. F is also present

may give

yellowish/greenish or

brownish/greenish.

Gem

.

in the

blue apatite shows strong dichroism: blue/yellow.

Blue and yellow apatites display a rare earth ("didymium," i.e. praseodymium + neodymium) spectrum. Yellow gems have 7-line group at 5800 and 5 lines at 5200. Blue gems give broad bands at 5120, 4910, and Spectral:

variety francolite.

Crystallography:

Hexagonal. Crystals usually prismatic

or stubby; massive, granular, compact; oolitic, earthy. Colors:

4640.

Colorless, green, white, blue, brown, yellow,

Luminescence: Yellow gems fluoresce lilac-pink in SW and LW (stronger in LW). Blue apatite fluoresces violet-

purple, violet, gray, pink, and various shades of most of these colors.

Refractive Indices Brirefrin-

Type

Locality

Chlorapatite Hydroxylapatite Fluorapatite Hydroxylapatite Fluorapatite

Japan

Carbonate apatite

Devonshire, England

with fluorine Hydroxylapatite Fluorapatite Fluorapatite Carbonate apatite

yellow

gemstone gemstone gemstone gemstone gemstone gemstone gemstone gemstone

Cut gemstone

—

Holly Springs. Georgia

Finland

Sweden Sweden

(with

Mn)

blue-green blue-green colorless

—

e

gence

SG.

—

1.624

005 007 004 005 003 005

1.634 1.632 1.633 1.603

1.630 1.629 1.630 1.598

004 003 003 005

— — — —

1.637 1.638 1.633 1.632 1.632 1.632 1.628 1.6401.642 1.632-

004 005 004 005 004 006 004 007

— — — —

1.658 1.651

1.633 1.646 1.634 1.629

1.653 1.644 1.629 1.641 1.631

321 3.2

3.22 3.27 3.14

(francolite)

Mexico

yellow

Canada

green

Maine

purple

St.

—

Paul's Rocks,

Atlantic

Cut Cut Cut Cut Cut Cut Cut Cut

Color

Ocean

Kenya

dark green

1.641

Zimbabwe

yellow-green yellow

Burma

dark green green

Brazil

deep blue

1.643 1.637 1.637 1.636 1.638

Canada

green

1

Mexico

Madagascar

Sri

Lanka (catseye)

Tanzania (catseye)

brown yellow

632

1.6471.649 1.6361.640

1

637

004

— — —

— 3.223.35

APHOPHYLLITE blue to sky blue, and violet material fluoresces greenish-

mauve (SW). Green apatite fluoresces greenish mustard color, LW stronger than SW. Man-

yellow (LW) or pale a

ganapatite fluoresces pink in SW.

Lazurapatite

found

45

a mixture of lapis and apatite that

is

is

in Siberia.

Name:

From

meaning

the Greek,

to

deceive because

mineralogists had confused apatite with other species.

Occurrence: Apatite is found in a wide variety of rock types. Igneous rocks are usually characterized by F and

OH

some containing Mn. Apatite occurs

varieties,

in

pegmatites, hydrothermal veins and cavities, metamor-

APOPHYLLITE Formula:

KCsuSUOarfF,

OH) 8H •

2

0.

phic rocks, and as detrital grains in sedimentary rocks

and phosphate beds. Blue: Burma; Sri Lanka; Blue-green: Arendal, also: Gravelotte,

Violet:

Crystallography: ular, prismatic,

Brazil.

Norway

(variety called moroxite);

East Transvaal, South Africa.

Germany; Maine;

California.

Green: India; Canada (trade-named bique; Madagascar; Spain; Burma. Brown: Canada.

Burma;

Trilliumite);

Mozam-

Italy;

Cut apatites are not

common

in

museum

gems (Brazil) are almost always small Burma produces 10 carat blue gems, but this color is very scarce in larger sizes. Yellow gems up to 15-20 carats are known from Mexico, but larger ones are collections. Blue (

Luster:

Vitreous, pearly on cleavage.

Hardness:

4.5-5.

Density:

Germany. Blue green and green from Sri Lanka and Burma. Catseye: Green catseyes also occur in Brazil, and yellow stones in Sri Lanka and Tanzania. Stone Sizes:

Colorless, white, grayish, pale yellow, pale green,

dark green, reddish.

Yellow: Durango, Mexico; Murcia, Spain; Canada; Brazil.

Colorless:

Colors:

Tetragonal. Crystals pseudocubic; tab-

sometimes pyramidal.

2.3-2.5.

Cleavage: Optics:

Perfect

=

o

1

direction. Fracture uneven. Brittle.

=

1.53-1.54; e

— );

Optically (+) or

(

Birefringence:

0.001 or

1.53-1.54 (variable).

uniaxial.

May appear

less.

isotropic.

None.

Pleochroism:

1-2 carats).

Not diagnostic.

Spectral:

Luminescence:

None.

quite rare. Violet stones are the rarest and smallest in

general, usually under 2 carats. However, the Roebling

purple apatite

SI

in

is

~ 100 grams, a superb

crystal.

Blue-green clean stones are usually less than 5 carats, rare

if

larger.

Green

apatite occurs in large crystals;

Canadian material has yielded 100 carat flawless stones.

The

gem may be

world's largest golden green

a 147 carat

stone from Kenya. Yellowish catseyes range up to about 15 carats, and green catseyes a bit larger (20 carats).

Comments:

Fluorapatite

is

the

commonest apatite vari-

abundant throughout the world, and is, in fact, the main constituent of bones and teeth. It is also the most abundant phosphorus-bearing mineral, especially collophane, the massive type that makes up large beds in some localities. Apatite is brittle and heat sensitive, and must be cut and worn with care. Properly cut ety.

Apatite

is

stones are truly magnificent, however, since they are

both bright and richly colored. suites of as

many

as 20 gems,

Mexican yellow

It is

all

possible to assemble

different colors.

perhaps the most abundant material available, and thousands of crystals exist that would cut stones up to 5 carats. Larger pieces are rare, however, even from this locality. The Mexican material may be turned colorless by careful heating. The catseye in Tanzanian stones may be so intense that the material resembles catseye chrysoberyl. apatite

is

Occurrence: Secondary mineral in basic igneous rocks, such as basalts and traprocks. New Jersey; Oregon; Washington; Colorado; Michigan; Virginia; Pennsylvania.

Guanajuato, Mexico; Brazil; Canada; Sweden; Scotland;

Germany; Ireland; Faroe Islands, Iceland; Bay ofFundy, Nova Scotia. Bombay, India: colorless crystals and also intense apple green color, due to Fe (Poona, India: o= 1.530, e= 1.533, birefringence 0.003, S.G.

Stone Sizes:

=

2.37).

Apophyllites are seldom faceted, and rough

to cut greater than 10 carats

is

very rare. Stones are

usually colorless, though green Indian material

is

also

cut.

SI: 15.4 (colorless, step-cut).

DG:

7.05 (colorless, Poona, India).

PC: 24.92

(free-form, Poona, India).

Comments:

Apophyllite

is

very brittle and fragile, with

an extremely perfect and easy cleavage. It is unsuited for jewelry, but colorless apophyllite is perhaps the whitest of

all

gems. The cut stones are so devoid of any trace of

color that they almost appear

silvery.

The

perfect cleav-

age dictates an orientation with the table of a faceted stone not perpendicular to the long axis of the crystals.

The

green, iron-rich apophyllite from India occurs in

AQUAMARINE

46

magnificent crystal groups, but facetable material

is

quite

scarce and usually smaller than the colorless variety.

Name:

From Greek words describing the tendency when strongly heated.

have yielded stones to 10 carats. of

apophyllite to exfoliate

AQUAMARINE

massive. Straw yellow crystals from Horschenz, Germany,

specimen

DG: PC:

1

Dimorphous

See

with Calcite.

Pb,

Sr, rarely

The hardness

huge transparent masses or

Zn.

Orthorhombic. Pseudohexagonal,

Crystallography:

gems

often acicular, chisel-shaped, prismatic; also mas-

sive,

columnar, fibrous,

stalactitic, coralloidal.

of aragonite

is

too low to

not as abundant or

crystals.

Faceted aragonite

are thus truly rare collector items.

Name:

Molina de Aragon, Spain.

Locality,

AUGELITE Colorless, white, yellow, gray, green, blue-green,

AhPCMOHh.

Formula:

lavender, reddish, brown.

Monoclinic. Crystals tabular and thick;

Crystallography:

prismatic; acicular. Also massive.

Vitreous to resinous.

Hardness:

3.5-4.

2.947 (pure). Usually 2.93-2.95; up to 3.0

Density:

Pb

is

Frequently

twinned.

Luster:

cut

crys-

tals

Colors:

known

widespread as calcite, except (in gem use) insofar as it is the major constituent of pearls. Faceted gems are almost always very small as opposed to calcite, which occurs in

also: Korite.

CaCOi +

Formula:

largest

10 carats.

10 (emerald cut, straw yellow, Bilin, Czechoslovakia).

allow for safe wear. Aragonite

ARAGONITE

1

:

Comments:

See: Beryl

The

from Bilin and weighs 7.85 (Germany). is

if

present.

Cleavage:

Colors:

White, yellowish, pale blue, pale rose.

Luster:

Vitreous. Pearly on cleavage surfaces.

Hardness: Distinct

1

direction. Fracture subconchoidal.

Density:

4.5-5.

2.696-2.75.

Brittle.

Optics:

a =

Biaxial (— ),

1.530;

2V =

Birefringence:

/}

=

1.681;

y =

Cleavage:

18°. Sector twinning observed.

y =

1

direction.

Luminescence: Pale rose, yellow, tan, green, rarely bluish in LW; may phosphoresce green in LW (Sicily). Yellowish, pinkish-red, tan, white in SW, also pink (Sicily).

Worldwide occurrences, especially in limestone caverns, hot springs, and in the oxidized zone of Occurrence:

locality, in

stubby twinned

= fi

0.014-0.020.

None.

Pleochroism:

Not diagnostic.

Spectral:

Luminescence: Occurrence:

None.

Crystals from the

Champion Mine, Mono

County, California, reach a size of about one inch; this locality

ore deposits.

1.570;

V -50°.

Birefringence:

Usually veil-type inclusions observed.

Molina de Aragon, Spain: type

good

1.590.

Biaxial (+), 2

Not diagnostic.

Inclusion:

direction,

a = 1.574; /J = 1.576; y = 1.588. White Mountain, California, material: a = 1.574;

Spectral:

1

Optics:

0.155.

None.

Pleochroism:

Perfect

1.685.

is

now depleted.

furnished cuttable

It

gem

material.

Masses occur at Keystone, South Dakota (nongem). Palermo Mine, New Hampshire.

crystals.

Potosi, Bolivia: in crystals. Bilin,

Czechoslovakia.

Sweden: massive. Uganda.

Austria; England; Peru; Namibia; Germany.

Agrigento, Sicily; with sulfur crystals.

Most gems

Chile; blue material.

Stone Sizes:

Guanajuato, Mexico; Laurium. Greece: blue aragonite.

nia material, are less than

1

carat

Many localities in the United States, including New Mexico.

Larger stones are exceedingly rare

South Dakota,

already a rare mineral.

Virginia, Colorado.

Fibrous aragonite from Wyoming, California, Iowa.

Stone Sizes: ats.

Faceted gems are usually only a few car-

Potential exists for

gems

much larger stones. Most faceted

are colorless, since colored material

is

usually

Comments:

Augelite

wear. However, the

is

gems

tals are true collector

complete collections.

from the Califorabout 3 carats. the case of what is

in existence,

soft

and

up in

to

brittle,

unsuited for

cut from rare transparent crys-

items and are seen only in very

1

AZURITE Name:

From

a

Greek word meaning

luster,

because of

the glassy appearance of the mineral.

Bourg d'Oisans, France: S.G. pockets

3.28, R.I.

=

47

1.68-1.69. in

in schist.

Switzerland: tinzenite.

AVENTURINE

Tanzania: magnesioaxinite.

See: Quartz.

Stone Sizes:

AXINITE Formula:

Mn,

(Ca,

tals;

Triclinic. Distinctive

PC:

16.5 (Baja California).

Geol. Mus., London: 0.78 (magnesioaxinite, Tanzania).

wedge-shaped

Comments: crys-

Cut axinites are usually intensely

with the brown and purple colors dominating.

also tabular.

exquisite but

rial is

Violet-brown, colorless, yellowish (Mn), pale

Colors:

violet to reddish

Luster:

(Mn), blue (Mg).

Vitreous.

Hardness:

3.26-3.36; magnesioaxinite

Good

Cleavage:

is

1

=

direction. Fracture

trichroic,

The mate-

almost never completely free of

flaws and feathers. Axinite

is

actually an extremely rare

cut

gem and could be one of the most magnificent because

of

its

and

rich colors

brilliance.

Clean stones over 5

carats are difficult to find and worthy of

6.5-7; variable with direction.

Density:

10

SI: 23.6 (brown, Mexico).

> Mn = ferroaxinite. If Mn > Fe = manganaxinite. If Mn > Fe and Ca < 1.5= tinzenite. Fe

Crystallography:

gems over

carats.

+ Mg — magnesioaxinite. If

rare in faceted

is

carats. Material

MghAhBSiXMOH).

Fe,

Axinite

from Baja California will yield gems to about 25 carats, but most stones, if clean, are less than 5

Group name.

Axinite

hard enough to be worn

is

museum display.

in jewelry,

though

it is

a bit brittle. 3.18.

uneven

to con-

Name:

From

a

Greek word meaning

axe, in allusion to

characteristic crystal shape.

choidal. Brittle. Optics:

a=

1.674-1.693;

/3

=

1.681-1.701;

y=

Magnesioaxinite: a = 1.656; /J = 1.660; y Biaxial (-), 2V= 63-80° or more.

May

turn

(

+

)

high in

if

=

1.684-1.704.

Mg.

Cu (CO

Formula:

1

J

)

2

(OH)

2.

Monoclinic. Crystals

Crystallography:

may be

large

and

perfect, tabular, prismatic; also massive, earthy, banded,

0.010-0.012.

Birefringence:

AZURITE

1.668.

stalactitic.

Dispersion:

Large.

Pleochroism:

mon

Intense in

all

Colors:

Light and dark azure blue.

Luster:

Vitreous (crystals) to earthy or dull.

colored varieties: cinna-

brown/violet-blue/olive green, yellow, or colorless.

Luning, Nevada: pale brown to colorless/deep brown/

Hardness:

3.5-4.

brownish red. Pale blue/pale violet/pale gray (magnesioaxinite). Sri

Lanka: reddish-brown/dark violet/colorless-yellowish.

Spectral:

4660, also

and 4150

Narrow line at 5120, broad lines at 4920 and at 4150. Sometimes lines visible at 5320, 4440, (latter

may be

strong).

Luminescence: RedinSW (Franklin, New Jersey). Dull red in SW, orange-red in LW (Tanzania: magnesioaxinite).

Density:

3.77.

Cleavage:

Perfect

Optics:

a =

Biaxial (+),

birefringence

=

0.010, S.G.

=

3.31).

Luning, Nevada: masses.

Pennsylvania;

New Jersey.

Cornwall, England: Germany; Norway; Finland; USSR: Japan; Baja California, Mexico, Tasmania.

direction. Fracture conchoidal.

1.730;

/J

=

Birefringence:

Spectral:

1.758;

y =

1.836.

2V -67°.

Pleochroism:

Occurrence: Axinite is found in areas of contact metamorphism and metasomatism. Yuba County, California: gemmy crystals. Also gem material from Coarse Gold, Madera County. California; New Melones, Calaveras County, California; Sri Lanka: ferroaxinite, cinnamon-brown (indices = 1.675/1.681/1.685,

1

Brittle.

0.

10.

Strong, in shades of blue.

Not diagnostic.

Luminescence:

None.

Occurrence: Secondary mineral in copper deposits. Chessy, France: chessylite, fine crystals in large groups. Morenci and Bisbee, Arizona: banded and massive material,

also crystals.

Eclipse Mine, Muldiva-Chillagoe area, Queensland.

gemmy crystals up to about 9 grams. New Mexico and other localities in that state.

Australia: Kelly,

48

AZURMALACHITE

Greece; USSR. Tsumeb, Namibia: fine, tabular

carbonate, malachite. Burnite

Italy;

in

small

crystals,

some

facetable

Facetable crystals are always

Stone Sizes: are

a mixture of azurite and

many

bits.

Zacatecas, Mexico: fine crystals (small).

gems

is

cuprite (copper oxide). Azurite occurs in fine crystals in

all less

stones, as they

than

1

carat.

It is

tiny,

and cut

pointless to cut larger

would be so dark as to be opaque. Dark is sometimes cabbed, and cabo-

localities, but in massive form is almost always mixed with malachite. In this form it is cut as very attractive cabochons and large decorative items, such as boxes. The intense blue color is distinctive and makes azurite very desirable among mineral collectors and gem

hobbyists.

blue crystalline material

chons may be several inches across.

Comments:

Faceted azurite

is a great rarity, but even extremely small stones are dark, virtually black. Azur-

malachite

is

a mixture of azurite

and another copper

Name:

In allusion to the color, derived

word lazhward, meaning

AZURMALACHITE

blue.

See: Azurite.

from the Persian

B

BALAS RUBY

See: Spinel.

BARBERTONITE

and

clay deposits,

rarely in cavities in igneous rocks.

Good crystals abundant worldwide. Meade County, South Dakota: fine brown

See: Stichtite.

crystals,

facetable.

BARITE

Colorado: exquisite blue crystals, some facetable

BaS0 +

Formula:

Ca,

4

(Ster-

ling area). Sr.

Illinois.

Thunder Bay

Orthorhombic. Tabular crystals, aggre-

Crystallography:

District, Ontario,

gates and rosettes; massive, granular, fibrous, earthy,

tals suitable for cutting.

stalactitic.

Rock Candy Mine,

reddish.

May be

crys-

Columbia, Canada: facetable

yellow crystals, up to 4 inches long.

White, grayish, yellowish to brown, blue, green,

Colors:

British

Canada: colorless

Cumberland, England:

color zoned.

fine crystals,

sometimes very

large,

facetable areas.

Many

Vitreous to resinous; pearly on cleavage.

Luster:

Hardness: Density:

many with

potential

3-3.5.

Stone Sizes: Large crystals are known, usually flawed, but many have facetable areas. English material will

4.50 (pure); usually 4.3-4.6.

Cleavage: Optics:

other localities worldwide,

for clean material.

Perfect

1

direction. Fracture even. Brittle.

a = 1.636; /3 = 2V/ =37°.

1.637;

y =

up to about 50 carats; one is known over 300 Yellow-brown crystals from France have been cut into gems as large as 65 carats. Colorado gems are usu-

yield stones carats.

1.648.

Biaxial (+),

ally 1-5 carats.

Birefringence:

Dispersion:

0.012.

0.016.

Weak

Pleochroism:

Brown

PC: 42 (golden-orange, cushion cut, British Columbia). 108 (dark brown oval, South Dakota).

crystal: straw

if

crystal

is

Comments:

colored.

yellow/wine yellow/violet.

Yellow crystal: pale yellow/yellow-brown/brown.

Green

Luminescence:

In

SW: white (Germany,

Ohio), blue-

ish white, yellow-green

LW:

like

marble and

hard to cut, and facet junctions tend to be rounded. The perfect cleavage makes wear very risky, and the low hardness would also prevent use in jewelry. In spite of the

crystal: colorless/pale green/violet.

green (Germany, England), gray (Germany). In

Massive white barite looks

could be used for decorative purposes. Faceted gems are

abundance of good crystals, cut barites are not commonly seen, especially in rich colors. With very few

green-

(Germany), pinkish white (Ohio),

exceptions, large stones could be obtained in almost any

cream-white (South Dakota).

desired color.

Occurrence:

Barite

is

common in low temperature hydroName:

thermal vein deposits; also as a component of sedimentary rocks,

sometimes

in large

beds; as concretions, in

Greek

cific gravity.

49

baros, heavy, because of the high spe-

BASTITE

50

BASTITE

Optics:

See: Enstatite.

=

o

1.757;

e=

1.804.

Uniaxial + ). (

BAYLDONITE Formula:

Birefringence:

CuhfAsCWOHh.

(Pb,

Dispersion:

Monoclinic. Fibrous concretions; mas-

Crystallography:

0.047.

0.046.

Pleochroism:

Strong: o

=

colorless, e

=

blue.

sive, granular.

Colors:

Various shades of yellowish green.

Luster:

Resinous.

Hardness:

Luminescence: LW. Occurrence:

Intense blue

SW only, no reaction to

in

Rush Creek, Fresno County,

California;

Texas.

4.5.

Belgium. Density:

5.5.

Optics: Biaxial

(

Only gem locality is in San Benito County, California, as superb crystals in a massive, fine-grained, white natro-

Not observed.

Cleavage:

a = 1.95; j) = + ), 2 V large.

Birefringence:

=

lite.

1.99.

Luminescence:

~2

crystals reach a size of

inches across, col-

areas are always very small.

Stone Sizes:

Always small because

flawed. Also, best color (along e) data.

tageous direction

Not diagnostic.

Spectral:

The

ored white and various shades of blue, rarely pinkish or colorless, zoned. Though crystals are large, facetable

data.

No

Pleochroism:

y

0.04.

No

Dispersion:

1.97;

tals,

giving smaller

stone on record

None.

in

is

crystals are badly

seen

in an unadvanterms of the flattening of the crysis

gems with good

color.

A

in SI, 7.8 carats.

large

The gem

was cut for a private collector but stolen in Most gems are under 1 carat, up to about 2-3

carats

Occurrence: Secondary mineral in Pb-Cu deposits. England; France. Tsumeb, Namibia: only major occurrence.

largest

of 6.52 transit.

carats.

The deposit has been gems sold, so benitoite

Larger stones are exceedingly rare.

worked out and available becoming very difficult to obtain in cut form. However, some new material is mined and marketed every year. largely is

Cabochons only from massive, fibrous matefrom Tsumeb.

Stone Sizes: rial

Comments:

Bayldonite

is

a nondescript greenish mate-

been cut into cabochons by enterprising collectors of the unusual. Cut bayldonites are a rarity, nonetheless, and are seldom seen in collections. The luster of cabochons is sometimes almost metallic and rial

that has

provides a curious appearance to the cut stones. Bayldonite

compact but too soft ties and pendants. is

for rings;

it

could be worn

in

AMNH:

3.57.

Comments:

Benitoite

is

one of the most beautiful of all

the rare gems, with the color of fine sapphire and the It was discovered in 1906 and thought to be sapphire. The dispersion is usually masked by the intense blue color. Benitoite is one of the

dispersion of diamond! first

most desirable,

attractive,

and scarce of

all

gemstones.

bola

Name:

After the occurrence

in

San Benito County,

California.

Name:

After Mr. John Bayldon.

BERYL BENITOITE Formula:

Crystallography:

Crystallography:

Hexagonal. Crystals triangular

in

shape,

flattened, very distinctive.

Sometimes zoned.

Luster:

2

Si60, 8

+

Fe,

Mn,

Cr, V, Cs.

Hexagonal. Crystals prismatic, elon-

gated or flattened, equant; often striated or etched; rolled pebbles; massive.

Blue (various shades), purple, pink, white, col-

Colors: orless.

Be 3 Al

Formula:

BaTiSi 3 09.

Colors:

Colorless, white, light green, olive green, blue-

green to blue (aquamarine), deep green (emerald), pink or peachy pink (morganite), greenish yellow, yellow

(heli-

Vitreous.

odor), pinkish orange, red (bixbite).

Hardness: Density:

Cleavage: Brittle.

Beryl

6-6.5.

is

one of the most familiar minerals because of

many famous gem varieties it offers. These specific gem types are named according to color and chemistry. The colorless variety, pure beryl, is termed goshenite. A the

3.64-3.68. Indistinct. Fracture

conchoidal to uneven.

trace of

manganese adds a pink or salmon-peachy-pink

BERYL color, and we have the variety known as morganite. Heliodor or golden beryl derives its color from ferric iron, and the color ranges from pale yellow to deep yellowish-orange. Aquamarine also gets its color from iron, but in the ferrous (reduced) state, and the range is from blue-green to deep blue. Emerald is the best known

color variety, the color of which, a fine, intense green,

due

to a trace of

beryl structure.

shades

Cr

is

is,

aluminum

is

in the

by definition, the green beryl

exist,

which are simply termed green

beryl,

where

chromium

spec-

Birefrin-

gence 1.584 1.576 1.572 1.570

1.591

biotite schist

1.582

(Emmaville)

Emerald

replacing

not present and does not reveal a

Occurrence

Locality

Australia (Poona]

chromium

colored by chromium. Other green beryls of various

Emerald

Austria (Habachthal)

51

1.578-1.579 1.575

schists

pegmatite

S.G.

Comments

0007 0006

2.74 2.73 0.005-0.007 2.69-2.70

0.005

268

Brazil

Anage Brumado

Bahia:

Carnaiba Salininha Minas Gerais (van] Goias (Sta. Terezinha)

1.584 1.579 1.588 1.589 1.578-1.581

mica schist

in talc

1.576 0.008 2.80 0.005-0.006 1.573 268 0.006-0.007 1.583 2.72 2.71 1.583 0006 1.572-1 .576 0.006-0.009 2.71-2 73

and

biotite schist

1.588-1.593 1.580-1.586 0.007-0.008 2.70-2.76 bluish-green

Colombia cracks

Chivor Mine,

dark

in

1.577-1 .579 1.570-1.571 0.005-0.006

schist

Muzo Mine

2.69

blue-green

calcite veins in

dark shale

Gachala Mine Burbar Mine trapiche emerald

Ghana

in biotite

poor

quality

.570-1.578 0.005-0 006 2.70-2.71 yellow-green 2.70 1.570 0.006 1.569 0.007 2.70 2.70 1.577 0006 1.582 0.007 2.70

1.580-1.584 1.576 1.576 1.583 1.589

India

Ajmer (unspecified)

1.595 1.593 1.593

schist

in biotite

Mozambique (Morrua)

1.585 1.585 1.585

0007-0010 0.007 0.008

2.74 2.73 2.73

Madagascar Ankadilalana Mine North Carolina

mica schist

Norway

in

(Eidsvoll)

in albite

matrix

granite

.581-1.585

1.589-1.591 1.588 1.590-1.591

1.581

583-1.584

0007 0.007 0.007

2.73 2.73 fluoresces 2.68-2.76

in

LW- UV

Pakistan

Mingora

1.596

Bucha

1.588

0.007

590

0.010

.588-1.593

0007

2.78

talc-quartz-carbonate

enclosed

in

ultramafics

Swat (general)

Zimbabwe

in

metamorphics

1.600 1.595-1.600

1

275-2.78

granite pegmatites

Victoria Province

cutting schists, also

Bubera Province

serpentines and

Shamva

fine

Province

mica

aggregates

Filabusi Province

Belingwe Province

Sandawana

1

.576-1 591 1.585 1.591

1.587-1.594 1.593-1.594 1.590-1.596

1

.572-1.585 0.004-0.007 2.67-2.74 with alexandrite also not gemmy 0.005 1.580 not gemmy 0.007 1.584 .583-1.588 0004 .586-1.588 0.005-0.007 .583-1 588 0.004-0.006 2.74-2.75

South Africa Transvaal, Gravelotte

(Cobra Mine,

etc.)

acid pegmatites and contacting schists

pegmatites and mica schists

Tanzania (Lake Manyara)

in

USSR

biotite-chlorite

(Urals)

schists

1.593-1 594 1.583-1.586 0.006-0.007 2.75-2.76

1.585

1.578-1.580 0.005-0.006 2.72-2.73 with alexandrite

0.006-0.007

2.74

1.589-1.590 1.581-1.582 0.007-0.009 0.007 1.588 1.581 0.006 1.586 1.580 1.592 0.010 602

2.74 2.68 2.79 2.77

1.588

1.581

Zambia Miku

in

schists

in

schists

Mufulira

Kitwe

Kafubu

1

BERYL

52

some

this also includes a deep green beryl colored by vanadium, which is technically speaking not emerald. A deep rose-red colored beryl, in small crystals from the Wah Wah Mountains of Utah, has been named bixbite; this color is also due to manganese; the material also contains Ti, Zn, Sn, Cs, Li, Rb, B, Zr, Nb, Pb, and traces

Australia: Biotite (abundantly); actinolite; calcite;

of other elements.

color zoning; garnets; hematite; feldspar; brown mica;

trum;

3-phase inclusions seen, tubes, "daggers," fluorite. Transvaal, Namibia:

Brown mica (makes gems dark

in

color); curved molybdenite crystals.

Zimbabwe: Fine long-curving tremolite needles; also 2-3 phase inclusions, short rods or fine curved fibers; negative crystals.

Vitreous.

Luster:

India:

Hardness:

7.5-8.

Cleavage:

Indistinct. Fracture

Oblong

cavities parallel to long crystal axis, with

gas bubbles; biotite crystals parallel to basal plane; fuchsite,

conchoidal to uneven.

2-phase inclusions; apatite crystals; groups of nega-

tive Brittle.

twin crystals with

comma

shape.

South Africa (Cobra Mine): Mica plates and 3-phase

Density:

inclusions.

goshenite: 2.6-2.9;

West Pakistan: 2-phase inclusions; thin

morganite: 2.71-2.90;

uid inclusions, few mineral crystals.

aquamarine: 2.66-2.80; emerald: 2.68-2.78;

cavities

Inclusions:

some

Beryl inclusions typically are long, hollow

sometimes filled with

liquid; the tubes are parallel

and run the length of prismatic crystals, sometimes have a brownish color and may contain gas bubbles. Negative

and tubes; actinolite, mica. Zambia: Biotite (black crystals) as small specks or dots; pinpoints, breadcrumb inclusions; also tourmaline (dravite) and magnetite. Material from Kitwe contains: rutile, chrysoberyl, muscovite, apatite, quartz; paragenesis indi-

metamorphic origin. Madagascar: brown biotite, muscovite, cates

apatite,

crystals are also seen, as well as flat inclusions that

resemble snowf lakes and have a metallic look, known as chrysanthemum inclusions. Aquamarines contain, in addition to the above, crystals of biotite, phlogopite, rutile, pyrite, hematite, and ilmenite in skeletal crystals that sometimes allow the cutting of star beryls. Some aqua-

marines contain snow-stars: irregular liquid droplets in These were especially noted in the Martha Rocha, a famous and large aquamarine. Red beryls from Utah display healed and unhealed fractures, growth banding, two-phase inclusions, quartz, and bixbyite. starlike patterns.

Habachthal, Austria: Straight, broad-stemmed tremolite

rounded mica

sphene; apatite;

plates; tourmaline; epidote;

rutile.

Colombia: Chivor Mine, 3-phase inclusions; pyrite; albite. Muzo Mine, 3-phase inclusions; parisite crystals (only known from Muzo mine), in yellow-brown prisms; calcite rhombs. Borur Mine, 3-phase inclusions. Gachala Mine, parallel growth bands, needlelike growth tubes; 3-phase inclusions: albite, pyrite; 6-sided cleav-

age cracks.

Coscuez Mine,

2-

tite,

and 3-phase

inclusions, pyrite, albite,

quartz, partially-healed fractures.

hema-

goethite, quartz, ilmenite, tourmaline, color zoning,

2-phase inclusions.

Norway: Mossy inclusions; also interconnected tubes (make crystals turbid). North Carolina: Quartz crystals sometimes seen. Beryl

Optics:

is

uniaxial

(

— ), and

refractive indices

vary with composition.

Goshenite: o

gence =

=

1.566-1.602; e

=

1.562-1.594; Birefrin-

=

1.578-1.600; Birefrin-

0.004-0.008.

Morganite: o

gence =

Inclusions in Emeralds

rods; biotite,

liq-

Tanzania: 2-phase and 3-phase inclusions; square-shaped

red beryl: 2.66-2.70.

tubes,

films;

=

1.572-1.592; e

0.008-0.009.

Aquamarine: o = 1.567-1.583; e = 1.572-1.590; gence = 0.005-0.007. Maxixe beryl, rich in cesium: o = 1.584, e

Birefrin-

=

1.592,

Birefringence 0.008.

Emerald: see table.

Red

beryl: o

gence

=

=

1.568-1.572; e

=

1.567-1.568; Birefrin-

0.004-0.008.

0.014 (low).

Dispersion:

Pleochroism:

Distinct in strongly colored varieties:

Aquamarine: blue/colorless (sometimes Maxixe-type aquamarine = blue/blue. Morganite: deep bluish-pink/pale pink.

greenish).

Heliodor: brownish-yellow/lemon yellow.

Bahia, Brazil: 2-phase inclusions; biotite; talc; dolomite

Emerald: blue-green/yellowish-green; rarely blue/yellowish

crystals; liquid films.

green.

Goids, Brazil: Pyrite, chromite, talc, calcite, hematite;

Red

notable also

USSR: bling

=

beryl: purplish-red/orange-red.

dolomite.

Actinolite crystals, singly or in groups, resem-

bamboo-cane; mica

plates.

Spectral:

broad band

Aquamarine spectrum due to at 4270, weak and diffuse band

ferrous iron; at 4560.

Also

BERYL weak

line

may be seen

at

5370 (absent

if

Madagascar:

stone has been

fine blue

heated).

specific localities.

Maxixe beryl has narrow line at 6950, strong line at 6540, and weak lines at 6280, 6150, 5500, and 5810. Emerald spectrum very diagnostic: there are fine lines in the red, weak ones in the blue and broad absorption in the violet; e and o have different characteristics: o: 6830/6800 doublet plus 6370 line; broad band 6250-5800; narrow lines 4775 and 4725. e: 6830/6800 doublet, very strong; no 6370 line, but see diffuse 6620 and 6460 lines; broad absorption band is weaker, no lines visible in the blue at all. Some Zambian emeralds contain Fe and display the spectral lines of aquamarine as well as emerald. Pleochroism in these gems is also distinctive: blue/

Jos, Nigeria:

beryl:

Bands

at

Burma and not

Occurrence:

Beryl occurs in granitic rocks, especially

granite pegmatites; also in schists (emerald),

metamor-

phic limestones (emerald) and hydrothermal veins.

The

occurrence of red beryl in rhyolitic volcanic rocks in the mountains of Utah is unique. The chemistry and mineralogy of this material is also singular. Beryl occurrences

San Diego County, in several localities— and gem material. Thomas Range, Utah: deep rose-red bixbite variety. Madagascar: in pegmatites and as alluvial material. Minas Gerais, Brazil: fine crystals and gem material.

Lake Manyara, Tanzania; Ghana; Madagascar. Colombia: at Chivor, Muzo, Gachala, Coscuez, and Borur Mines.

Swat area, West Pakistan. Zambia: at Miku and Mifulira, also other locations. Eidsvoll, Norway: in granite.

Red

Wah Wah Mountains.

Stone Sizes: Beryl crystals weighing many tons have been found in pegmatites, but these are never of gem quality. Aquamarines and green beryls, however, may be completely transparent and still be very large. A crystal weighing 243 pounds was found in Brazil in 1 9 1 that was completely transparent; another in 1956 weighed about 135 pounds. Some very large gems have been cut from type of material. Morganites are usually smaller, up

about 6 inches

known up

to

in

diameter, and the largest emeralds

are less than 10 pounds. Bixbite occurs in crystals

about 2 inches

in length,

and these are seldom

transparent, even in small areas.

Madagascar:

gemmy

material,

much

Namibia:

in

of

it

crystals.

deep orange colored

gemmy.

Connecticut: small but fine colored crystals, some

SI: 61.9 (colorless, Brazil).

Morganite: SI: 287 (pink, Brazil) and 235 (pink, Brazil); 178 (pink, California); 113 (peach, California); 56 (pale pink,

Maine; North Carolina; Mt. Antero, Colorado. Connecticut: some gem.

58.8 (heart-shape, Madagascar).

weight

not much gem material.

BM:

Rio Grande do Norte, Ceara, the world's major source of

aquamarine gems.

USSR:

large cut

gems with carved

1500 carats, tables carved

tables, total

in religious motifs.

82.25 (yellow).

ROM: is

-*

Heliodor:

San Diego County, California:

Mursinsk,

118.6 (pink, catseye).

BM: rose-red crystal from California weighing 9 pounds. PC: three very

other localities; Brazil

Brazil).

Madagascar). Natural Hist. Museum, Paris: 250 (pink, Madagascar).

AMNH:

gemmy. Aquamarine:

Brazil, also

very few stones

Goshenite:

ROM:

pegmatites.

Zimbabwe. Minas Gerais,

The

are less than 3 carats.

Leningrad Museum: 598.7 (Rose-pink, step cut,

Brazil: greenish yellow to fine

fine

beryl:

Utah, especially

Madagascar); 330 (dark orange,

Heliodor:

color.

Africa; Arusha, Tanzania;

known

California:

Madras and Kashmir, medium blue

Habachthal, Austria; Brazil; USSR; Sandawana, Zimbabwe; Poona, Australia; Cobra Mine, Transvaal, South

this

fine crystals

Lanka: aquamarine has been found,

there.

Hiddenite, North Carolina.

to

Morganite:

Sri

common

India: at

Goshenite:

Maine; South Dakota; Utah; Colorado; North Carolina; Connecticut; Idaho; New Hampshire. Canada; Mexico; Brazil; USSR.

fine color.

Emerald:

are worldwide.

California;

abundant material, some

more than 50

Rossing, Namibia: in pegmatites.

4250, 4800, 5300, and 5600-5800.

Luminescence: Emerald sometimes green in SW; very seldom weak red, orange in LW. If red fluorescence is seen, the color is visible in the Chelsea filter. Fluorescence is quenched by Fe, as in the South African and Indian emeralds. Morganite may fluoresce weak lilac.

material,

Australia: Mt. Surprise, North Queensland (small).

yellowish-green.

Red

gem

53

also other localities.

78.8 (yellow, step cut, Brazil).

SI: 133.5 (yellow, Madagascar); 43.5 (golden catseye,

Madagascar); 17.5 (yellow, USSR).

Aquamarine: A crystal was found

in

Marambaia, Teofilo Otoni,

BERYL

54

Brazil, blue-green,

an irregular prism 19 inches long

and 16 inches across and weighing 10.2 kg. It was transparent end to end. The famous Martha Rocha aquamarine, found in Brazil, weighed 134 pounds and 1

more than 300,000 carats of superb blue gems. even larger crystal found in 1910 weighed 229

yielded

An

pounds but yielded only 200,000 carats of cut gems. 67.35 (blue) and 60.90 (greenish); 879 (sea-green,

be large and flawless, but these are best displayed in museums rather than worn. Emerald is acknowledged as one of the most desirable gemstones, and aquamarine has recently sustained an unprecedented rise in price.

Morganite has similarly risen in both demand and value. Goshenite has never achieved great popularity and colorless beryls are easy to obtain at modest cost. The same

BM:

general

oval).

colored gems over 10-15 carats are

AMNH: 272, 215, and

160; also 355 (Sri Lanka), 144.5

(Brazil).

Hyde Park Museum, New

York: 1847 carats.

SI: 1000 (blue-green, fine color, Brazil); 911 (blue, Brazil); 263.5 (blue,

USSR);

71. 2 (pale blue, Sri Lanka);

comment applies to yellow beryls, although darker-

in greater demand. and olive-colored stones are not well known to the gem-buying public and therefore are in slight demand. Aquamarine of large size (15-25 carats and very deep blue color has become extremely scarce and very

Green

beryls

expensive. Large

gems continue

to

be available but

at

A major problem in aquamarine is the

66.3 (pale blue-green, Maine); 20.7 (pale blue,

ever higher prices.

Madagascar); 15.3 (blue-green, Idaho); 14.3 (blue,

which can be irradiated to improve the color. The deeper blue is not stable, however, and such gems may rapidly fade in sunlight. The dichroscope reveals the Maxixe beryl, both windows remaining blue whereas in normal aquamarine one window would be colorless or pale yellowish. Some controversy exists as to the definition of emerald. The type of definition involving a shade of green or depth of color is totally inadequate because it is completely subjective. A rigorous, adequate, and objective definition involves simply the presence or absence of chromium and the corresponding presence of the chromium absorption spectrum, plus (usually) a red color in the Chelsea filter. The deep green beryls colored by

Connecticut).

Other Colors: SI: 2054 (green-gold,

and 914 (green, Madagascar); 98.4 (pale green, Brazil); 40.4 (pale green, Connecticut); 23 (green, Maine); 19.8 (brown, star, Brazil). Emerald: The largest emerald crystal extant weighs 16,020 carBrazil); 1363, 578,

Brazil); 133.5 (golden yellow,

and is from the Muzo Mine in Colombia. Many museums around the world display fine and large emeralds, both crystals and faceted gems, as well as some ats

carvings and tumble-polished stones. SI: 117 (green,

Colombia); 10.6 (North Carolina); 4.6

(green catseye, Colombia); 858 carat crystal

— "the

so-called Maxixe-type beryl,

vanadium

are therefore not emeralds, despite potentially

Gachala."

high prices.

Moscow: 136 (nearly flawless, deep blue-green, step cut) (in the Diamond Fund). Kunsthistorisch.es Museum, Vienna: 2681 carat vase,

tone, with pleochroism blue-green/yellow green. Studies

showed

carved.

also revealed as iron bands in the absorption spectrum.

Topkapi Museum, Istanbul: 6-cm hexagonal 8-cm crystal; 3 other large crystals.

crystal;

Emeralds from Zambia may display an unusual blue that this

Zambian

is

crystals

due

to a high content of iron (0.73%),

may be

intensely color zoned, with

fine

near colorless cores and dark green rims, almost

Banque Markazi, Teheran: Many cabochons between

watermelon tourmaline. Recently discovered emeralds from Itabira, Minas Gerais, Brazil, rival the best Colombian

100 and 300 carats; one is 175 carats, another 225. There are also faceted gems of 100 and 110 carats; unmounted cabochons of 320, 303, 144.4, and two

others over 250 carats.

stones in quality.

down

"Devonshire emerald," a crystal 51 weighs 1384 carats, fine color.

mm.

long,

AMNH:

are typically light bluish-green

the c-axis.

Bixbite

BM:

They

like

is

a very rare, raspberry-red beryl from Utah,

seldom seen as a cut gem and then only

in

very small size

(1-2 carats).

Crystal 1200 carats, fine color, the Patricia emerald; 630 carat crystal — "the St. Patrick Emerald."

Catseye and star beryls are strange curiosities. Catseye aquamarine and emerald are known, sometimes rather

Banco de

Oriented ilmenite inclusions in pale green aquamarine from Gouvernador Valadares, Brazil, create a brown body color and cause a sheen or Schiller effect that, when included in a cabochon, creates a star. Black star beryls have no fluorescence or distinctive absorption spectrum and are also known from Alta Ligonha, Mozambique. They strongly resemble black star sapphire and are often confused with the latter. Most aquamarine is heated at 400-450°C to reduce any ferric iron present and eliminate the accompanying

la

Republica, Bogota, Colombia: collec-

tion of superb crystals

from 220

to 1796 carats.

PC: Atahuallpa emerald, 45 carats, set in Crown of the Andes, a magnificent gold headpiece with 453 emeralds totaling 1521 carats. Emilia crystal from Las Cruces Mine (near Gachala) weighs 7025 carats.

The beryls are among the most popular, and also the most expensive, of all gems. A wide range of color is represented, from colorless to black. Beryls can Comments:

large.

BISMUTOTANTALITE yellowish color. This has the effect of material pure blue, which

is

making blue-green

considered a more desirable

color in the marketplace. This heating

is

done

just after

cutting and does not affect the value of the cut stone,

aquamarine is heated in this manner. Emeralds from Muzo and Chivor can be distinguished in a general way, because Muzo material is yellowish green, whereas that from Chivor is blue-green. It somesince virtually

The

however.

inclusions in emerald

material, and hence cut

may be

Stoneham, Maine: only cuttable crystals ever found; also crystalline masses up to 1-2 inches, but only small clean areas within such masses could be cut. Stone Sizes:

gems less than 5 carats. The mineral gems are only known from Maine

All

all

times takes a trained eye to see the distinction

easily chipped.

55

itself is

very rare, and

Stones up to 10 carats have been cut, but they

localities.

are not clean. SI: 2.5, 3.3, 3.9, 5.10 (all Maine).

in color,

may weaken

the

gems are fragile and brittle and Care should always be taken in

wearing an emerald, especially a ringstone.

Names: Beryl is of Greek origin but uncertain derivation. Aquamarine comes from Latin for sea water, in allusion to the color. Morganite is named after J. R Morgan, the investment banker and financier. Goshenite is named after Goshen Massachusetts. Heliodor is from the Greek helios (sun), in allusion to the yellow color. Emerald is from the Greek smaragdos (green), through the Latin "smaragdus" to Middle English esmeralde. Bixbite is named after Maynard Bixby of Utah.

DG: PC:

HU:

5.70 (colorless, Maine). 7.82, 8.77, 4.32 (colorless, Maine).

6.22 (colorless, Maine).

Comments: and since there

Beryllonite

much

not

is

is

really not suited for wear,

available only as small colorless stones,

it is

incentive to

make

jewelry out of

it.

However, beryllonite is one of the truly rare collector gems and should be greatly prized as a cut stone. The cleavage makes gems hard to cut.

Name:

In allusion to the composition.

BISMUTOTANTALITE

See

also: Tantalite, Stibiotan-

talite.

Formula:

BERYLLONITE NaBeP0

Formula:

(Bi,

Sb) (Ta,

4.

Orthorhombic. Crystals sometimes

Crystallography: 4.

Nb)0

large; massive;

stream pebbles.

Monoclinic. Crystals tabular or prismatic, usually etched. Twinning common. May be

Colors:

Light

brown

pseudo-orthorhombic.

Luster:

Adamantine

Colors:

Colorless, white, pale yellow.

Streak:

Yellow-brown to black.

Luster:

Vitreous; pearly on cleavage.

Hardness:

Crystallography:

Hardness: Density:

Density:

5.5-6.

2.84 (pure); usually 2.80-2.85.

to black. to submetallic.

5.

8.84 (Brazil).

Cleavage:

Perfect

1

direction. Fracture subconchoidal.

Brittle.

Cleavage:

Perfect

1

direction,

good

1

direction. Frac-

Optics:

a =

Biaxial (-), 2

1.552;

y =

0.009.

None.

Not diagnostic.

Luminescence:

(

2.388;

+ ),2V=

p = 2.403; y

=

2.428.

80°.

1.561.

0.010.

Pleochroism: Spectral:

1.558;

Biaxial

V= 68°.

Birefringence:

Dispersion:

p =

a =

Optics:

ture conchoidal. Brittle.

None.

Hollow canals and fluid cavities arranged parallel to crystal axis. Material from Stoneham, Maine, has tubes, gas bubbles, and acicular crystals.

Birefringence:

0.040.

No

Dispersion:

No

Pleochroism: Spectral:

data.

Not diagnostic.

Luminescence: Occurrence:

Gamba

data.

Hill,

None.

Pegmatites.

Uganda; Acari,

Brazil.

Inclusions:

Occurrence: Granite pegmatites. Newry, Maine: opaque white crystals, not really possible to cut.

Stone Sizes:

Cut gems always small,

less

than 5 carats.

Comments: Extremely rare as a cut gem, even in very complete collections. Many of the minerals in the tantalite group have been faceted; bismutotantalite is perhaps the rarest of them all. The color is attractive, but

BIX BITE

56

low hardness and good cleavage make use

in

jewelry

unadvisable.

On

Name:

BORACITE

account of the composition.

Orthorhombic. Pseudo-tetragonal. Crys-

Crystallography: tals

BIXBITE

MgJ^OnCl.

Formula:

small and equant.

See: Beryl.

Colors:

Colorless, white, gray, yellow, pale to dark green,

bluish-green.

BLENDE

See: Sphalerite. Vitreous.

Luster:

BLOODSTONE

Hardness:

See: Quartz.

Density:

BOEHMITE

See: Diaspore.

Optics: Biaxial

P&AgaCusChifOH)*

•

H

2

0.

None. Fracture conchoidal

(

a = 1.658-1.662; + ), 2 V= 82°.

Birefringence:

Tetragonal. Pseudocubic. Crystals usu-

Crystallography:

2.95.

Cleavage:

BOLEITE Formula:

7-7.5.

ally

cube shaped, sometimes modified by other faces,

and

in parallel

Dispersion:

Not diagnostic.

Spectral:

Streak:

Blue with a greenish tinge.

Luminescence:

Luster:

Vitreous, pearly

Choctaw

Salt

=

direction,

1

2.05; e

=

good

1

direction.

2.03.

Stone Sizes:

Birefringence:

considered an extreme

0.020.

Comments:

None.

rence

Not diagnostic.

Luminescence:

Broken

Hill,

is

Boracite

Gems

over 2 carats would be

rarity.

is

not a

common mineral

restricted to salt deposits

;

its

occur-

and similar environ-

ments, resulting from the evaporation of sea water in enclosed basins. However, the mineral has no cleavage

None.

Secondary mineral

Occurrence: Chile;

Boracite crystals are very small and yield

stones up to 1-2 carats.

Pleochroism:

Otis, California.

only cuttable crystals. Crystals usually small, pale colored.

Uniaxial (— ).

Spectral:

Dome, Louisiana;

evapo-

in

and Hanover districts, Germany: source of the

Stassfurt

Perfect

o

greenish (SW).

Aislaby, England; Luneville, France.

5.05.

Optics:

Weak

Occurrence: Sedimentary deposits formed rite sequences (sea water).

on cleavage.

3-3.5.

Cleavage:

1.668-1.673.

None.

Indigo blue to Prussian blue, blackish blue.

Density:

y=

0.024.

Colors:

Hardness:

1.662-1.667;

0.011.

Pleochroism:

growths.

=

to uneven.

in

Cu and Pb deposits.

N.S.W., Australia.

Boleo, Baja California: magnificent single crystals and

and a high hardness, so

more abundant. The

V2

a

shame it is not larger or gems are usually deli-

cate shades of light blue and green, and the dispersion is

groups on matrix, with single crystals up to nearly

it is

colors of cut

moderate. Cut boracite

tor

is

one of the rarer of

collec-

gems.

inch.

Stone Sizes: Crystals up to 2 cm on an edge have been found. Crystals, however, are usually nearly opaque, and facetable material is exceedingly rare. Stones up to about 1 carat have been cut, and even these are not

Name:

In allusion to the borax in the composition.

BORNITE Formula:

CusFeS.*.

entirely clean.

Crystallography:

Comments:

Cut boleite

is

strictly for collectors, since

ally

Tetragonal. Crystals rare, twinned; usu-

massive, compact.

Faceted gems of any transparency the rarest of all gemstones. The color is so attractive that any available stones would be quickly snapped up by collectors.

cent purple color. Streak:

Light grayish black.

Name:

Luster:

Metallic; opaque.

it is

soft

and very

rare.

should be considered

among

Boleo, Santa Rosalia, Baja California, Mexico.

Colors:

Copper red

to bronze. Tarnishes to an irides-

BRONZITE Hardness:

cm. Some Density:

5.08.

AMNH:

Traces. Fracture uneven to conchoidal. Brittle.

Cleavage:

Crystals from Brazil are up to 12

Stone Sizes:

3.

Occurrence: Low temperature copper deposits. Connecticut; Virginia; North Carolina; Montana; Arizona; Colorado; California. Canada; Chile; Peru; England; Italy; Germany; South Africa; Madagascar.

gems have been

large

X

8

cut.

23 (emerald cut, Brazil), 19 (round, yellow).

and

SI: 41.9

57

17.0 (yellow, Brazil).

PC: 24 (yellow, Brazil). Most gems are 1-10 carats, or even

smaller.

Cut stones

Bristol,

Cabochons could be very

Stone Sizes:

large, several

inches long, because the massive material from ore veins is

available in large pieces.

Comments:

Bornite

is

when

The

they tarnish.

The

material

effort of cutting.

After Ignatius von Born, eighteenth-century

Faceted stones are often flawed

will

Monoclinic. Crystals equant, prismatic,

Crystallography:

Name:

Formula:

Colors:

Light copper-red, violetish.

Streak:

Reddish brown.

Luster:

Metallic; opaque.

7.59-8.23.

Cleavage:

None. Fracture subconchoidal to uneven.

Brittle.

Luminescence:

5.5.

Good

1

1.609;

y =

None.

Massive material could cut gems to hundreds of carats but only as cabochons. Stone Sizes:

1.621-1.623.

Comments: 0.019-0.021. tors,

although

color

0.014.

Pleochroism:

Weak — merely a change in shade of color.

is

Breithauptite it

extremely

is

is

Hydrothermal mineral

in

pegmatitic

is

The

material

in cut

gist.

BRONZITE

See: Enstatite.

is

interesting

not very rare but

form.

After G. W. A. Breithaupt, a

cavities.

Palermo Mine, Grafton, New Hampshire. Conselheira Pena, Minas Gerais, Brazil: only source of gem material, in crystals up to large size.

The

veined with streaks of native

gangue minerals, providing

seldom encountered

Name:

in jewelry.

both unique and attractive. Some-

times the reddish sulfide patterning to the color.

Occurrence:

a curiosity cut for collec-

lovely, a delicate reddish or violet with

metallic luster that

None.

is

could be worn with care

silver or colorless

Not diagnostic.

Luminescence:

in reflected light.

direction. Fracture conchoidal. Brittle.

a = 1.602; /J = + ),2V= 71°.

Birefringence:

Strong

Occurrence: In massive Ni sulfide ore bodies. Cobalt district, Ontario, Canada; Sarrabus, Sardinia; Adreasburg, Harz, Germany.

2.980-2.995.

Spectral:

rare, usually

5.5.

Pleochroism:

Dispersion:

Hexagonal. Crystals are

massive, compact.

Vitreous.

(

unlikely that they

NiSb.

Luster:

Biaxial

it is

BREITHAUPTITE

Colorless, pale yellow, yellowish-green, greenish.

Optics:

so a clean

After occurrence in Brazil.

Colors:

Cleavage:

Gems lovely.

ever be cut.

Density:

spear-shaped; also striated.

Density:

in large sizes,

is

gem over 15 carats is a great rarity. Many crystals that are in museums would yield very large gems, but these are

Hardness:

NaAMPCXMOHk.

Hardness:

in 1944.

See: Serpentine.

BRAZILIANITE Formula:

was discovered

are suitable only for collections, but the color

Crystallography:

mineralogist.

BOWENITE

Brazilianite

is

not rare, so cabochons have no great value beyond the

Name:

Comments:

retained as crystal specimens and

suitable only for cabochons.

bronzy color rapidly tarnishes in air to a magnificent iridescent color display, mostly purple, but also with blue and green tones. Bornite is too soft and brittle for anything but a collector curiosity, although cabochons are quite attractive

over 5 carats are scarce today.

German

mineralo-

BROOKITE

58

BROOKITE

Hardness:

Formula:

Density:

TiCh.

Orthorhombic. Occurs only

Crystallography:

in crys-

2.39.

Cleavage:

Perfect basal cleavage. Sectile, plates flexible.

prismatic, pyramidal; often striated.

tals; tabular,

o

Optics:

Brown, yellowish brown, reddish brown, dark

Colors:

brown

2.5.

=

=

1.559-1.590; e

1.580-1.600.

Uniaxial (+); sometimes biaxial with small 2V.

to black; rarely blue.

0.010-0.020.

Birefringence:

Adamantine

Luster:

Hardness:

to submetallic.

Cleavage:

a =

Optics:

Luminescence:

Indistinct.

2.583;

Occurrence:

=

/J

2.584;

y =

in

transmitted

light.

Not diagnostic.

Spectral:

4.14 normal; range 3.87-4.14.

Density:

None; colorless

Pleochroism:

5.5-6.

None. In

low temperature hydrothermal veins

in

serpentine, chloritic and dolomitic schists, and meta-

2.700-2.740.

morphic limestones.

Biaxial (+).

Asbestos, Quebec, Canada: Fibrous masses up to several

0.122-0.157.

Birefringence:

feet in length; also cuttable pale blue masses.

Pleochroism: Strong: yellow-brown/reddish-brown/ orange to golden brown. An hourglass-shaped zonal coloration is sometimes seen in bluish crystals.

Occurrence:

In gneisses, schists

and sometimes

in igne-

New

rocks.

York: hydrothermal deposits.

Switzerland: typical Alpine deposits. Gerais, Brazil; Dartmoor, England; France;

Stone Sizes: are opaque.

Always

Comments:

Brookite

Brucite

less

USSR.

than 1-2 carats; larger stones

transparent only

in

is

among

small fragments. Cuttable crystals

the rarest of

all

gems. Most stones are

Comments:

Brucite

are

After the English mineralogist and crystallogra-

BRUCITE Formula:

2.

variety

crystals, platy aggre-

sometimes

acicular.

Also

difficult to cut,

and

After Archibald Bruce, an early American min-

who

BUERGERITE

See Tourmaline.

See: Azurite.

BUSTAMITE (Mn, CabSiiO^.

Formula:

White, pale green, gray, bluish. Manganoan

to vitreous; pearly

on cleavages.

Triclinic. Crystals tabular, usually

rounded and rough; massive. Colors:

Pale flesh pink to brownish red.

Luster:

Vitreous.

Cleavage: Optics:

variety yellow to brownish-red, brown.

Waxy

described the species.

first

5.5-6.5.

3.32-3.43.

Perfect

1

direction,

good

1

direction.

foli-

ated, massive, fibrous, scaly.

Luster:

extremely

Name:

Density:

Hexagonal; tabular

Manganoan

Colors:

is

eralogist

Hardness:

Mg(OH)

Crystallography: gates.

The major

Asbestos, Quebec, which

known.

Crystallography:

H. Brooke.

J.

is

in

private collections.

pher

very rarely facetable.

a very dark-colored mineral,

are exceedingly rare, and attractive-looking cut stones

Name:

is

has yielded pale blue gems up to 1+ carats.

BURNITE

are

van),

{

California.

Minas

Sweden (manganoan

only a few faceted stones in the h~\ carat size range

Magnet Cove, Arkansas: contact metamorphic Tirol,

York: Small crystals.

California; Italy; Scotland;

source for cuttable material

ous rocks; contact deposits. North Carolina; Somerville, Massachusetts; Maine:

Ellenville,

New

Brewster,

Stone Sizes:

None.

Luminescence:

cm

across.

USSR.

Not diagnostic.

Spectral:

New Jersey: Fibrous aggregates. Lancaster County, Pennsylvania: Plates nearly 20 Hoboken,

Strong, ~0. 131.

Dispersion:

Biaxial

a = 1.662-1.692; = {-),2V= 30-44°.

Birefringence:

Pleochroism:

1.674-1.705;

y=

1.676-1.707.

0.014-0.015.

Weak:

rose red/orange/orange.

BYTOWNITE Spectral:

Comments:

Not diagnostic.

Luminescence:

Bustamite

very similar in appearance

The Japanese crystals are Mn. The color, when fresh, is paler than Bustamite may also be fibrous, and then yields

and properties

None.

is

59

to rhodonite.

very rich in

Occurrence: Manganese ore bodies, usually of metasomatic origin. Cornwall, England; Langban, Sweden. Franklin and Sterling

Hill,

New Jersey:

Iwate and Yamagata prefectures, Japan:

Broken Hill, N.S.

=

x

10

gems, but these are extremely

bustamites are very attractive, especially

Faceted pinkish

shades, but stones over 1-2 carats are very rare collec-

gemmy crystals.

tor items.

Mn 2V =

has high

cm; S.G. =

3.41,

1.688,/?= 1.699,y= 1.703, Birefringence 0.015.

ill

The cleavage makes cutting

Faceted gems are usually small,

less

Name:

After the discoverer of the mineral,

than 5

and mostly in the 1-2 carat range. Catseyes are also known, up to about 5 carats.

difficult

and wear

advised.

mente. Stone Sizes:

rare. in the

in fine crystals.

W., Australia: this material

content, in crystals up to 2

39°, a

rhodonite.

fine catseye

carats,

BYTOWNITE

See: Feldspar.

M.

Busta-

c CAIRNGORM

SW:

See: Quartz.

red, orange,

lemon

yellow, shades of green, shades

of blue, pink, white.

LW:

CALAMINE CALCENTINE CALCITE calcite

=

Occurrence: Occurs in all types of rocks as the most abundant carbonate mineral on Earth. Found in veins, ore deposits, and as a constituent of rock limestone and marble. Crystals often large (many inches) and transparent. Onyx is the material of most limestone caves, usually banded in shades of tan and brown. Iceland spar is colorless calcite, transparent, sometimes in large masses. The name alabaster refers to gypsum and is incor-

See: Korite.

Dimorph

of

ARAGONITE.

Sphaerocobaltite

tine

= Flowstone

ter;

Marble.

Also Cobalto-

= C0CO3; Onyx =

Traver-

(found in caves); Iceland spar; Alabas-

rect

CaCOj.

Formula:

orange, dull pink, tan, yellow, blue, gray.

See: Hemimorphite.

Crystallography

:

when

applied to calcite.

Gem material is commonly

seen from the following localities: Missouri (colorless),

Hexagonal R (

huge array of forms; massive;

)

.

Crystals

Baja California (brown), Canada,

common in a

New

York, Montana,

England, Mexico, Iceland (colorless), and the

stalactitic; chalky.

USSR

(pale yellow).

Colors:

Colorless (Iceland spar), white, gray, yellow,

Stone Sizes:

shades of pink, green, blue, purplish red (Co).

Rough material can be very

dreds of carats). Colorless material Luster:

Density:

Optics:

emerald-cut.

up

3.

2.71 (pure) to 2.94.

Perfect rhombohedral (3 directions).

Cleavage: e

=

1.486-1.550; o

=

Spectral:

7.5 (cobaltocalcite, Spain).

PC: 4,440

Birefringence:

(colorless); 1156 carats (colorless, twinned); 474 (yellowish, USSR). NMC: 606 (light yellow cushion cut, with sulfide inclusions; Bancroft, Ontario, Canada); 168.2 (colorless, Portuguese cut). HU: 1260 (Bancroft, Ontario, Canada). ROM: 183 (colorless, Balmat, New York). GIA: 48 (yellow, USSR).

0.172-0.190.

Strong.

Pleochroism:

Brown

to 50 carats,

DG:

1.658-1.740.

Uniaxial (— ).

Dispersion:

large (hun-

usually step-cut or

material from Baja is usually seen normal range 5-25 carats. Purplish red material from Paramca, Spain (cobaltian) is not transparent, usually cut 1-5 carat size. Onyx is opaque and yields cabochons and carvings of any desired size. SI: 75.8 and 45.8 (golden-brown, Baja).

Vitreous to pearly.

Hardness:

is

None.

Any lines seen are due

to specific

elements as

impurities.

Luminescence: Common and from many around the world.

localities

60

common and abundant through-

Comments:

Calcite

out the world.

The material has little

is

intrinsic value since

CARNELIAN it

not scarce. However, calcite

is

age

The

3 directions.

in

one of the most

is

minerals to cut because of perfect cleav-

difficult of all

cost of a faceted stone

is

there-

fore mostly in the labor of cutting. Normally, a faceted

stone breaks during cutting, and the finished

much

gem

50 carats

stones cut from material from

is

extremely

many

up, but the lack of scarcity value

rare.

might turn not encouraging to

potential calcite cutters.

Onyx

is

usually cut into slabs,

made

Name:

From

but

is

a

the composition: Ca, Na, and

Si.

into vases, lamps,

Formula: (Na,K,Ca)6-8(Al,Si) 12 024(C0 3 ,S04,Cl),-2 nH 2 0. Note: If S0 4 > COi, the species is called Vishnevite. The Cl-rich variety is called microsommite. Crystallography:

Colors:

Name:

Hardness:

derived from the Latin calx, meaning

is

it

CANCRIN1TE

and many other decorative objects. It is usually banded in shades of brown, green, and buff. Marble is a metamorphic rock often used in construction and in making decorative carved objects. Coloration in the form of banding and streaks is due to impurities. ashtrays, bookends,

Calcite

in

Faceted

localities

is

being called "canasite" has no canasite

new, distinct species.

is

smaller than the originally intended size. There-

fore, a cut calcite over

rial

61

Hexagonal. Crystals prismatic, but rare;

usually massive.

Colorless, white, yellow, orange, pink to red-

dish, pale blue, bluish gray.

Luster:

Vitreous; pearly

on cleavage;

greasy.

5-6.

lime.

Density:

2.42-2.51; Vishnevite: 2.3.

Cleavage:

CALIFORNITE

Perfect

1

direction. Fracture uneven. Brittle.

See: Garnet. Optics:

o

Formula:

(Na,K) 5 (Ca,

Mg)4(Si 2

O

Monoclinic. Occurs

Crystallography: ally

Mn,

s)5

(OH,F)3.

Greenish yellow.

Luster:

Vitreous.

in tiny grains, usu-

Biaxial

Perfect

1

direction,

a = 1.534; f} = (-),2K -53°.

Birefringence:

good

direction. Brittle;

1

1.538;

y =

1.543.

0.009.

Occurs

in

pegmatite

in

the Khibina Tun-

Stone Sizes: Massive blocks up to several inches have been found. Material is cut as cabochons and decorative objects.

None

in

UV

Occurrence: Primarily in alkali-rich rocks; also as an alternation product of nepheline. Iron Hill, Colorado; Kennebec County, Maine. Norway; Rumania; Finland; USSR; Korea; China; Zaire; India; Uganda; Kenya. Bancroft District, Ontario, Canada: fine gemmy material.

Masses occur up

is

to several pounds, but

usually in veins a few inches across.

The

as "canasite"

is

material usually seen on the market

purplish in color.

It

is

fused with another purplish material, a serpentine family

known

frequently con-

member

of the

as stichtite. However, stichtite

Comments: Cancrinite is one of the most attractive of all opaque or translucent gem materials. It is a bit too jewelry. Cancrinite

may be

Recent research seems to indicate

is

mate-

worthy of it

often

contains numerous hard inclusions. Faceted gems even as small as

Name:

1

carat are considered great rarities.

After Count Cancrin, Finance Minister of Russia.

granular.

that, in fact, the

is

tricky to cut because

elongated fibers that have a kind of lustrous

sheen, almost asbestiform, whereas canasite

It is

usually cut as cabochons and beads. The Canadian material is orangy yellow in color, with a greasy luster. Faceted stones are exceedingly rare and always less than 1-2 carats.

soft for average wear, but its distinctive color

Comments:

in

Not diagnostic.

cancrinite

USSR.

occurs

Weak.

Stone Sizes:

Not diagnostic.

Occurrence: dra,

is

0.022 (cancrinite); 0.002-0.012 (vish-

Birefringence:

Luminescence:

2.707.

Spectral:

1.495-1.503. (cancrinite).

+ ).

Spectral:

grinds to feltlike powder.

Optics:

(

Dispersion:

5-6.

Cleavage:

=

nevite).

Colors:

Density:

1.507-1.528; e

optically

twinned.

Hardness:

=

o = 1.490-1.507; e = 1.488-1.495 (vishnevite). Uniaxial (-); chlorine-rich variety (microsommite)

CANASITE

CARNELIAN

See: Quartz.

.

CASSITERITE

62

CASSITERITE Sn0 +

Formula:

except

ever, very rare 2

fine

Fe,Ta,Nb.

problem.

Tetragonal. Crystals prismatic, pyrami-

Crystallography:

gemstone — it

is

small fragments. Cassiterite

under

5 carats are not

dal; also botryoidal, reniform with a radial fibrous struc-

rare stones, but large clean

Twinning common. Brown, brownish black, black, colorless, Colors:

Name:

ture.

gray,

The Greek word

gems

for tin

among

is

a

no cleavage

is

unfortunate that cuttable rough

It is

Cassiterites

in

rather hard, and there

is

so scarce.

the rarest of

definitely are. is

kassiteros.

yellowish, greenish, red.

CATAPLEIITE Streak:

White, grayish, brown.

Luster:

Adamantine

Na

Formula: to vitreous; greasy

on fracture

ZrSiiO>)

2

•

2H 0; Dimorphous 2

with Gaidon-

nayite.

surfaces.

Hexagonal; crystals thin hexagonal Also lamellar masses; twinned. Gaidonnayite is orthorhombic. Crystallography:

Hardness:

6-7.

plates.

6.7-7.1; pure material 6.99.

Density:

Imperfect. Fracture subconchoidal to uneven.

Cleavage:

pink, yellowish red. Rarely pale blue or colorless.

Brittle.

o

Optics:

Uniaxial

zoned

Light yellow, yellowish brown, brown, salmon-

Colors:

(

=

=

2.006; e

biaxial, 2

Vitreous, greasy, or dull.

Luster:

2.097-2. 101

+ ); anomalously

V= 0-38°, usually in

Hardness:

5-6.

crystals.

Density: Birefringence:

2.65-2.8.

0.098.

Cleavage: 0.071 (nearly twice that of diamond).

Dispersion:

Pleochroism:

Weak

to strong; greenish yellow or yellow-

brown/red-brown. Most Spectral:

visible in strongly

colored crystals.

Not diagnostic.

Luminescence:

Perfect

o=

Optics:

direction, imperfect 2 directions;

1.596;

e=

1.624.

Uniaxial (+). Birefringence:

None.

1

also parting.

0.280.

None

Pleochroism:

Occurrence: Prinicipal ore of tin; occurs in medium to high temperature veins; metasomatic deposits; granite

Spectral:

pegmatites; rhyolites; alluvial deposits.

Luminescence:

in colorless

gems.

Not diagnostic.

None

reported.

Alaska; Washington; California; Nevada; South Dakota;

Occurrence:

South Carolina; Virginia. Canada; Mexico; Cornwall, England; Portugal; Japan; China; New South Wales. Australia. Araca Mine, Bolivia: source of most of the gem material known: yellow, gray, colorless and light yellowish brown to reddish brown.

Langesundfjord District, Norway; Magnet Cove, Arkansas.

Spain:

gem

Erongo

material in yellowish to red cuttable pieces.

tinfields,

Stone Sizes:

Namibia: gem material.

Clean

cassiterite

gems over

Greenland; USSR; Madagascar. Ste. Hilaire, Quebec, Canada: cuttable

Mt.

1

carat are

The

Comments:

Ste. Hilaire,

PC:

Formula:

:

From

catapleiite

is

carat have been cut

from

is from form of tiny

only reported cut catapleiite

Quebec, Canada,

in the

G reek words meaning rare minerals because

usually associated with other rare minerals.

CELESTITE SrS0 4

Crystallography:

SI: 10 (yellow-brown, Bolivia).

DG:

1

colorless gems.

Name

9.6 (brownish, Tasmania); 11.83 (brown, England);

under

crystals.

Canadian material.

up to several pounds in weight, but these are opaque and are sometimes cut into cabochons. Pale brown to dark brown gems up to 15 carats have been cut; slightly flawed stones up to 25 carats are known, mostly Bolivian material. 28.16 (brownish).

Gems

Stone Sizes:

Mt.

quite rare. Masses occur

Alkalic rocks and pegmatites.

ally tabular; also

.

Orthorhombic. Crystals common, usunodules, earthy, massive.

14.85, 9.51 (brownish, Bolivia).

Comments: Cassiterite has tremendous dispersive fire, much more than diamond, that is visible in properly cut pale-colored gems. This lighter-colored material

is,

how-

Colors:

Colorless, white, gray, blue, green, yellow, orange,

and red shades. Luster:

Vitreous; pearly

on cleavage.

CERUSSITE 3-3.5.

Colors:

Turquoise-blue shades, cerulean blue.

3.97-4.00.

Luster:

Earthy, dull.

Hardness: Density:

Cleavage:

Perfect

direction,

1

good

1

direction. Frac-

ture uneven. Brittle.

a =

Optics:

1.622-1.625;

V=

p =

1.619;

y =

1.624;

y=

Dispersion:

shades of indigo blue, bluish

cabochons

Luminescence: Blue in SW. Blue or May phosphoresce blue-white.

it

sometimes

deposits,

dull yellow in

is

in

many

fine color.

only.

Comments:

Ceruleite

truly exquisite color.

also found in hydrothermal vein

igneous rocks.

Clay Center, Ohio; Colorado; Chittenango York;

LW.

Celestite occurs in sedimentary rocks, espe-

cially limestones;

Huanaco, Chile: original material. Southern Bolivia: cabbing material of

Stone Sizes: Nodules are usually small, less than 1 inch and up to several inches in size. The material yields

Not diagnostic.

Occurrence:

in the vicin-

of copper deposits, like turquoise.

Cornwall, England.

0.014. in

index ~ 1.60. Very fine grained.

Sedimentary material formed

Occurrence:

green, and violet. Spectral:

Mean

Optics:

50°.

Weak,

softer).

2.7-2.8.

1.631-1.635.

0.009-0.012.

Pleochroism:

may be

1.631.

ity

Birefringence:

6.5 (conflicting data,

Density:

Madagascar gems: a = Biaxial (+), 2

Hardness:

63

Falls,

New

localities in California.

is

a little-known

gem

material of

takes a very high polish easily and

It

and the color of the polished gems

is far deeper extremely rare in fine, solid, cuttable pieces and consequently is rather ex-

quickly,

than that of the rough nodules. pensive.

Few cut stones are

It is

to be seen in

museum collec-

and the total amount of fine Bolivian material may not exceed several hundred pounds. A major problem tions,

San Luis Potosi, Mexico; Bristol, England; Girgenti, Sicily; Madagascar; Germany; France; Austria; Italy; Switzerland; USSR; Egypt; Tunisia. Lampasas, Texas: gemmy material (blue). Put-in-Bay, Strontian Islands, Lake Erie: gemmy material. Tsumeb, Namibia: gem material. Canada: orange crystals.

with ceruleite

and

porosity, rendering the material too soft

is

and wear. This problem can be

fragile for cutting

solved by plastic impregnation. Such impregnated ceruleite

has a density of 2.58.

Name:

In allusion to

its

color; the Latin caerulea

means

sky blue. Celestite gems are usually under 3 carats and are generally colorless or pale blue, often step-cut. However, some gems are known in the 30 carat range, and there is no reason why large transparent crystals cannot be found and cut.

Stone Sizes:

DG:

NMC: PC:

Madagascar). 3.11 (orange step-cut, Ontario, Canada).

20.1 (blue,

2.98 (blue,

New

CERUSSITE PbCOj.

Formula:

Orthorhombic. Crystals common, elon-

Crystallography:

gated, tabular, often twinned and striated; acicular, massive.

Colorless, white, gray, "smoky," greenish (Cu

Colors:

York).

inclusions), yellowish.

Comments:

Celestite

is

seldom seen

haps because faceted gems have

little fire

colorless or pale blue, rarely orange. fragile,

in collections, per-

and are usually are soft and

Gems

hard to cut, and cannot be worn with

Celestite

is

strictly for collectors; large,

gems are indeed

rare,

safety.

clean faceted

Adamantine

Luster:

Latin coelestis

means

celestial, in allusion to

the delicate and lovely pale blue color often displayed by this mineral.

Hardness:

to submetallic; vitreous; resinous;

3-3.5.

Distinct

Extremely Optics:

CERULEITE

6.55.

Cleavage:

Biaxial

Usually massive, compact, earthy.

1

direction. Fracture conchoidal.

brittle.

a =

1

.804;

(-),2V=

Birefringence:

CuiAMAsO^OH),,.

Crystallography:

due

pearly.

Density:

Formula:

is

whereas transparent crystals per se

are not.

Name:

Dark gray or black material

to inclusions.

Dispersion:

Pleochroism:

/J

=

2.076;

y =

2.079.

9°.

0.274.

0.055 (greater than diamond).

None.

CEYLONITE

64

Hardness:

Not diagnostic.

Spectral:

Luminescence: Pinkish orange (Utah) or yellow shades in LW. Pale blue or shades of green in SW.

Secondary mineral in the oxidized zones of lead deposits. Many localities known: Tiger, Arizona; Colorado; Idaho; South Dakota; Utah; New Mexico; Montana; Nevada; California. Broken Hill Mine, Zambia; Dundas, Tasmania; Broken Occurrence:

Hill, N.S. W.,

Australia;

Monte Poni,

4-5.

Density:

2.05-2.16.

Cleavage: Optics:

Distinct

1

direction. Fracture uneven. Brittle.

=

Variable; R.I.

Uniaxial

1.470-1.494.

+ or (— ). )

(

Not diagnostic.

Spectral:

Luminescence:

None.

Sardinia; Leadhills,

Scotland.

Occurrence:

Tsumeb, Namibia: source of the largest and finest gem material; colorless, gray and yellowish, in masses up to several pounds (completely transparent).

rocks; also hot spring deposits.

Large masses of transparent rough are

Stone Sizes:

known from Tsumeb, Namibia, that could cut stones several thousand carats. The real problem is cohesion

of

known from 2-6 carats; the material is from and Tsumeb, Namibia. (pale yellow, Tsumeb, Namibia); 109.9 (smoky,

Catseyes are

Tiger, Arizona,

4.7

Tsumeb, Namibia).

NMC:

Tsumeb, Namibia). PC: 408 (brownish-gray oval, Tsumeb, Namibia); 262 (emerald cut, colorless, Tsumeb, Namibia). 71.25 (colorless octagon,

Comments: since

it

Cut cerussite

as beautiful as

is

has higher dispersion,

is

usually free of

diamond any body

and has an adamantine luster. However, cerussite is extremely soft and one of the most brittle and heat sensitive of all minerals. Cutting a gem is a major chore, and cutting a very large one without breaking it is almost impossible. Consequently, faceted cerussite is one of the rarest of all gems. Abundant rough material is available among the thousands of crystals and crystal fragments recovered from Tsumeb, Namibia. Few cutters, however, have the skill and knowledge required to successfully fashion a gem from this rough. The cost of a cut stone will therefore largely reflect the cutting cost. Time, patience skill, and tender loving care are essential. color,

Name: cial lead

From

the Latin cerussa, the

name

of an

See: Spinel.

2

0.

Hexagonal. Crystals rhomb-shaped, tabular; frequently twinned. Crystallography:

Colors:

Colorless, white, yellowish, pinkish, reddish

white, salmon color, greenish. Luster:

Vitreous.

Stone Sizes: Cut chabazites are always very small, usually less than 1-2 carats. Crystals are never entirely transparent, and often only one corner of a pinkish or colorless crystal can be cut. Very few chabazites have been cut at all,

and they are seldom seen

Comments:

Chabazite

is

in

museum

collections.

too soft for wear.

The

colors

are pale but attractive. Unfortunately, clean material

extremely scarce. Chabazite

is

is

not a terribly difficult

material to facet, but finding suitable material

is

not

one of the rare gems that are seldom discussed or heard about. There may be only a handful of cut gems easy.

This

is

in existence.

Name:

From

the

Greek chabazios, an ancient name

applied to certain materials.

CHALCEDONY

See: Quartz

CHALCOSIDERITE

See: Turquoise

CHAMBERSITE Formula:

M113B7O13CI.

up

to

1

Orthorhombic. Crystals shaped cm on edge.

Colors:

Colorless, brownish,

Luster:

Vitreous.

Hardness:

•

Nova Scotia, Canada; Greenland; USSR; India;

Australia; Czechoslovakia.

tetrahedra,

CaAhSi^n 6H

district.

Scotland; Ireland; Italy; Germany; Hungary;

Crystallography:

CHABAZITE Formula:

Bay of Fundy

artifi-

carbonate.

CEYLONITE

Nevada; California; Oregon; Colorado; New Jersey; Hawaii.

of

large stones.

57:

Cavities in basalt and other basic igneous

Density:

3.49.

None.

a =

Optics: (

purple.

7.

Cleavage:

Biaxial

lilac,

+ ),

2

1.732;

Birefringence: Spectral:

/J

=

1.737;

V ~ 83°. 0.012.

Not diagnostic.

y -

1.744.

like

CHIOLITE None.

Luminescence: Occurrence: ber's Hill salt

scenic stones due to the admixed minerals.

Occurs in brines in storage well dome. Chambers County, Texas. Cut stones are not

Stone Sizes:

are usually under 2 carats. in

at Bar-

really transparent

and

shape and are cut by beveling and polishing off part of

Some

is

chatoyant.

Name:

Gems are generally triangular

65

For the

CHERT

locality.

See: Quartz.

CHIASTOLITE

See: Andalusite.

are, in a sense, truncated crystals with their surfaces

CHILDRENITE

Series to Eosphorite

polished.

Fe.

Comments:

Formula:

the tetrahedron of a crystal to save weight. Cut stones

Chambersite is an exceedingly rare minmight be gathered from the locality information.

eral, as

Crystals are generally tiny and are recovered by skin

much

diving to a depth of as

as 70 feet in brine.

Cut

(Fe,Mn)AlP04
Colors:

Brown

Name:

Luster:

Vitreous to resinous.

the Texas locality.

Hardness:

CHAROITE K(Ca,Na) 2 Si4O 10 (OH,F)

Formula:

H

•

2

Monoclinic; crystals thin, acicular

Crystallography:

Density:

0.

Luster:

Vitreous.

Hardness:

to yellowish

brown, golden yellow.

5.

3.2 (pure

Fe end member).

Poor. Fracture uneven to subconchoidal.

Cleavage:

a = 1.63-1.645;

Optics: Lilac to violet, in various shades.

0.

(i.e.,

fibrous).

Colors:

2

exceeds

often doubly terminated.

stones are merely curiosities and very few exist.

From

H

Mn

Orthorhombic. Crystals equant, pyram-

Crystallography: idal, platy,

2

if

Biaxial

(-),2V=

=

1.65-1.68;

y =

1.66-1.685.

0.030-0.040.

Birefringence:

Pleochroism:

5-6.

/3

40-45°.

Distinct: yellow/pink/colorless to pale

pink.

Density:

2.54-2.68.

None.

Luminescence: Cleavage:

Indistinct; fracture splintery.

May show

Spectral:

a = Biaxial + ). Optics:

1.550;

/J

=

1.553;

y =

lines of iron

spectrum.

1.559.

Occurrence:

In granite pegmatites

and hydrothermal

(

vein deposits.

Birefringence:

0.009.

Pleochroism:

Distinct; colorless/rose-pink.

Luminescence: Spectral:

Cornwall, England; Greifenstein,

None

Stone Sizes:

Occurrence: This unique and striking material comes only from the Chary River area in the Murun Massif, Northwest Aldan, Yakutsk, ASSR, USSR. The material is intimately mixed with prismatic orange crystals of tinaksite, pale greenish gray microcline, and greenish black crystals of aegirine-augite. This makes a unique, distinctive, and highly ornamental rock. The geology is that of nepheline and aegirine-bearing syenites contacting limestones; the charoite rock occurs in metasomatic for

making bookends,

It is

a massive material suitable

vases, goblets

has been widely marketed since

its

and cabochons.

It

original description

Stone Sizes:

more

tals

up

Large blocks suitable for making objects a in size are available.

South

much

Charoite also produces

Childrenite occurs in brown opaque crys,

to several inches long. Transparent material

smaller,

and facetable

crystals yield stones

about 3-4 carats. In general, cuttable material series

is

DG:

up

is

to

in this

closer to the eosphorite end.

3.58 (Brazil).

Comments: Cut childrenite is a great rarity, and all gems are small. Cut eosphorite is more abundantly available,

though both materials are very scarce.

Name:

J.

G. Children, English mineralogist.

CHIOLITE Formula:

in 1978.

foot or

Custer,

Minas Gerais, Brazil: gemmy crystals. These are found to be Fe:Mn =1:1 and could be called childro-eosphorite.

reported.

Not diagnostic.

bodies at the contact.

Germany;

Dakota.

Na.sAhFu.

Crystallography: tals,

commonly

in

Tetragonal; minute dipyramidal crys-

masses.

66

CHLORASTROLITE

Colors:

Colorless, white.

Luster:

Vitreous.

Cleavage: None. Fracture uneven. weakly magnetic. Optics:

Hardness:

Sometimes

2.08-2.16. Isotropic.

3.5-4.

Not diagnostic.

Spectral:

Density:

2.998.

Cleavage: Optics:

=

R.I.

Brittle.

Perfect

o

=

=

1.349; e

None.

Luminescence:

direction.

1

Occurrence: In igneous rocks rich in, olivine; in serpentines; in stream and beach sands. Sometimes in mas-

1.342.

Uniaxial (— ).

sive deposits of large size.

Birefringence:

0.007.

California: Oregon: Washington: Wyoming: Maryland: North Carolina: Pennsylvania. Canada: Cuba: Norway: USSR: France: Zimbabwe: India.

None.

Pleochroism:

Not diagnostic.

Spectral:

Any

Stone Sizes:

None.

Luminescence: Occurrence:

Ivigtut,

Miask, Urals,

USSR:

rial.

Greenland: associated with in a cryolite

cryolite.

pegmatite.

Chiolite has nothing It is

much

crystals

none

Comments:

Chromite

is

shiny and black, and

to offer in the

makes

a

curious-looking cabochon with no special attraction.

have little value because the material dant but are cut as curiosities only.

is

The stones

extremely abun-

very soft, has perfect cleavage, has no

appealing colors, and

usually small and nondescript.

is

However, it has joined the ranks of minerals that have been cut by facetors who must try their hand at everything clean enough to cut. There may be less than one or two dozen cut stones in existence. Chiolite exists solely as a curiosity in the

gem

Name:

In allusion to the composition.

CHRYSOBERYL BeAl

Formula:

+

Fe,Ti.

Orthorhombic. Crystals tabular or priscommon; also massive and as water-

matic, sixling-twins

worn pebbles. Yellowish green, yellow, gray, brown, blue-green,

Colors:

deep green,

See: Pumpellyite.

red, violet. Rarely colorless. Alexandrite

varies in color with incident light: green, blue-green, or

pale green in daylight; mauve, violet to red, purplish in

CHLOROMELANITE

CHONDRODITE

4

2

Crystallography:

From the Greek words for snow and stone because in its white appearance it is similar to cryolite, whose name means ice-stone.

CHLORASTROLITE

Also called Catseye, Alexandrite.

world.

Name:

CHROMITE

some deep reddish

to contain very tiny facetable areas, but thus far

Occasionally, a cabochon has a reddish color.

quite rare.

Comments: way of a gem.

could be cut from massive mate-

size

possibility exists for

have been discovered.

Stone Sizes: Always tiny, 1-2 carat range, if clean. Large, clean fragments do not exist for cutting. The mineral itself is

The

See Jadeite.

See:

Chromite

incandescent

light.

Catseye

brown

to pale yellow,

Luster:

Vitreous.

is

usually dark yellowish

honey yellow, greenish.

Humite Group. group, extensive solid-solution

Hardness:

8.5.

series.

Note: Magnesiochromite

= MgCr

2

4;

Hercynite

= FeAbOv

Density:

3.68-3.80; colorless 3.70;

gems usually

higher,

alexandrite highest.

FeCr

Formula:

2

04.

Cleavage: Crystallography: 1

cm on

Isometric. Octahedral crystals up to

Streak:

1

direction,

Black, reddish brown.

Brown.

Biaxial

a= (

1.740-1.759;

+ ), may

Submetallic; opaque, translucent in thin splinters.

Hardness: Density:

5.5.

4.5-4.8.

/3

=

also be (-),

1.747-1.764;

y=

1.745-1.770.

2V= 70°. Indices vary with

Fe content. Colorless (Sri Lanka): a

Luster:

seldom observed, varies

edge; massive. Optics:

Colors:

Distinct

to poor. Fracture conchoidal. Brittle.

Australia:

a

1.768-1.777;

SG =

Birefringence:

=

1.740;

1.756-1.765;

==

3.72-3.74.

0.008-0.012.

fi

=

==

1.745;

y =

1.750.

1.761-1.772; y

=

CHRYSOBERYL

AMNH: 14A

Properties of Alexandrite from Various Localities

(emerald-cut, yellowish green)

67

— may

be

world's finest of this color). Urals

Sri

Lanka

Density Optics

Burma

Zimbabwe

Brazil

3.71

3.68

3.64-3.80

1.746 1.748 1.755 0.009

1.747 1.748 1.756

1.749 1.752 1.758 0.009

Lanka); 58.2 (The Maharan.

Birefrin-

1.749 1.753 1.759 0.009

1.745 1.749 1.755 0.010

0.009

gence

Sri

(Sri

Lanka); faceted: 114.3

Lanka, yellow-green); 120.5 (Sri Lanka, green); 46.3 Lanka, brown); 6.7 (Bra-

(Sri

a P r

Lanka, gray-green); 47.8

SI: catseyes: 171.5 (Sri

(Brazil, yellow-green); 31.7 (Sri zil,

dark green

Iranian

star); alexandrites: 65.7, 16.7 (Sri

Crown Jewels:

Lanka).

141.1 (Sri Lanka, chartreuse); 25

(gray-green catseye). Institute

of Mines, Leningrad (St. Petersburg): Urals crysalexandrite, 6x3 cm, consisting of 3 crystals.

tal cluster,

Dispersion:

0.015. Distinct, in shades of yellow

Pleochroism:

and brown.

Alexandrite: deep red/orange-yellow/green. (Note:

gem anomalous:

Burma

purple/grass-green/blue-green.)

gems have strong band Lankan gems. Also may

Yellowish and brown

Spectral:

4440 due to Fe, especially Sri be bands visible at 5040 and 4860. Alexandrite has narrow doublet at 6805/6875, with weak, narrow lines at at

6650, 6550, and 6490 and broad band at 6400-5550. Total

absorption below 4700.

Fersman Museum (Moscow): Alexandrite crystal cluster 25 x 15 cm, with crystals up to 6 x 3 cm, from Urals. PC: U.S. dealers have reported alexandrites up to about 50 carats. Catseyes up to 300 carats are in private collections. Faceted gems over 40-50 carats are very rare. 185 carats; a superb 120 carat yellow Brazilian

Japanese collection, and a 79.30 carat brown Sri Lankan oval and a 66.98 carat flawless yellow Brazilian stone in a U.S. collection. The world's largest faceted chrysoberyl is a 245 carat flawless oval, slightly yellowish green, from Sri

Luminescence: Alexandrite fluoresces weak red in SW and LW; pale green chrysoberyl from Connecticut noted yellow-green in SW. In catseye, there are short needles

Inclusions:

and tubes

parallel to the long axis of the crystal. Liquid-filled cavi-

with 2-phase inclusions; stepped twin planes.

ties

Occurs in pegmatites, gneiss, mica schist,

Occurrence:

dolomitic marbles; also found as stream pebbles and

gem of gem in a

Stones reported include a flawed yellow Brazilian

Lanka. Transparent chrysoberyl makes a handsome

Comments:

gem and

one of the hardest and toughest for is not distinct, and the hardness is near that of sapphire and ruby. In general, the bright yellow and yellow-green shades are the most desirable, but some of the browns are also striking and handsome. Properly cut gems are very brilliant, although they lack fire due to low dispersion. The chrysoberyls from Australia have unusually high refractive indices and could

faceted

is

jewelry purposes. Cleavage

detrital grains.

South Dakota; Colorado; Maine; necticut;

USSR;

New

New Hampshire; Con-

York; Finland; Zaire; Madagascar; Japan.

alexandrite of finest quality in mica schist, near

possibly be misidentified as yellow-brown sapphires.

Catseye gems of such minerals as apatite, tourmaline,

and diopside are well known, but when the term catseye is

Sverdlovsk. India: catseyes with sillimanite fibers, from Kerala. Brazil (especially Jacuda, Bahia): fine facetable material;

also catseyes, alexandrite.

Zimbabwe: Sri

Lanka:

fine alexandrite, intense color change.

all

types,

some

of the world's finest catseyes,

also alexandrite; faceting material

used alone

it

always refers to chrysoberyl.

The

silk in

such a gem, which creates the chatoyancy,

so fine that a microscope

colors, rarely effect within the

colorless.

Burma: some alexandrite;

light

rarely colorless facetable

chrysoberyl.

Anakie, Queensland, Australia: yellow-green chrysoberyl.

The

Stone Sizes:

largest alexandrites

Russian locality are chrysoberyl

is

from the

in the 30-carat range.

known up

to several

hundred

classic

Facetable carats,

and

catseyes of similar size have been found. Star chrysoberyls are

known but

are very rare.

needed

is

is

stone obliquely usually creates a shadow

gem, such

that the side

away from the

a rich brown, while the side facing the light

is

yellowish white, creating the so-called milk and honey

look characteristic of the finest chrysoberyls. This ap-

pearance

in a large (over

20 carats) stone results

in

very

high value.

Alexandrite is well known today as a scarce and costly gem. Stones over 5 carats are very rare, especially if the color change is good. The quality of the color change with illumination conditions

is

BM: 29.4 (Sri Lanka, yellow-green); 4b(Hope Chrysoberyl,

andrite quality and value.

flawless oval catseye); 43, 27.5 (Sri Lanka, alexandrites).

blue-green to green (daylight)

ROM:

descent light). Brazilian

42.72 (Sri Lanka, chartreuse green).

is

to resolve the fibers.

Consequently, the eye is the sharpest of any catseye gemstone. The optimum color is a honey brown, and light striking the

all

The eye in a

chrysoberyl catseye often has a shimmering blue tone.

the primary basis of alex-

Optimum vs.

gems tend

colors are intense

purple-red

(in

incan-

to have pale colors.

CHRYSOCOLLA

68

pale

mauve

to pale blue-green, but finer

found reeently (12(K)

ppm)

in limited quantity.

of the element gallium (replacing Al) have

been detected alexandrite

is

some

in

Brazilian alexandrite. Sri

Lanka

often deep olive green in sunlight, whereas

Russian stones are bluish green

gems

gems have been amounts

Substantial

Zimbabwean

in daylight.

are a fine emerald green color in sunlight but are

usually tiny (under

carat)

1

clean.

if

The

color change in

Comments:

Chrysocolla often forms as a gel mixed

with silica and hardens to a blue material that a chrysocolla-saturated quartz. This material

wears well, and is often seen in jewelry. Chrysocolla mixed with malachite is often sold as Eilat Stone and comes from many localities; the color is blue to blue-

= 2.8-3.2.

green, S.G.

Material of fine blue color but very

tends to be brittle and crumbles easily, mak-

little silica

Stellarite

from the rough from

chrysocolla and quartz. Parrot-wing

Names:

Catseye

is

named from

eye in the stone to the narrow

the resemblance of the the eye of a cat.

iris in

Another name for this gem, cymophane, is from Greek words meaning appearing like a wave because of the opalescent appearance of some crystals. Alexandrite is named after Czar Alexander II of Russia, on whose birthday the gem was found. Chrysoberyl is derived from the Greek chrysos, meaning golden, in allusion to the

basically

very hard

(7),

Zimbabwean gems is among the best known, and it is a shame that large clean stones are virtually unobtainable this locality.

is is

ing

impossible to cut stones for jewelry purposes.

it

the trade

is

name

for a light blue mixture of is

a mixture of chrys-

ocolla and jasper, with a brownish green appearance.

Name: glue.

Greeks

Greek Chrysos means golden and

In

name was

This

kolla

means

applied to a material used by the

now fulfilled by name from Eilat, Gulf of

soldering metals, a function

in

borax. Eilat Stone takes

its

Aqaba, Red Sea.

CHRYSOLITE

See: Olivine.

usual yellowish color of this mineral.

CHRYSOPRASE

CHRYSOCOLLA

CHRYSOTILE

(Cu,Al) 2 H 2 Si20 5 (OH) 4

Formula:

•

nH

2

See: Quartz. See: Serpentine.

0.

CINNABAR Monoclinic. Crystals are microscopic,

Crystallography:

Blue, green, and blue-green in various shades.

Colors:

Mixed with matrix of quartz and oxides of Cu, Mn, adding brown and black colors. Luster:

Vitreous

(if silicified),

2-4 (as high as 7

Hardness:

if

waxy,

HgS.

Formula:

in aggregates; cryptocrystalline, opalline.

Fe, and

Hexagonal. Usually massive, fine

Crystallography:

grained; crystals are prismatic or rhombohedral and characteristically twinned, especially those

from China.

Colors:

Scarlet red, brownish red, brown, black, gray.

Luster:

Adamantine

dull.

to submetallic; massive varieties

heavily silicified, or includull, earthy.

sions in quartz).

Hardness:

None. Fracture uneven

Cleavage:

to conchoidal.

Density:

brittle.

Optics:

a = 1.575-1.585;

/3

=

1.597;

y =

1.598-1.635.

If

readings

material

may be

Luminescence:

is

included in quartz,

In the oxidized

Perfect

o

Optics:

Uniaxial

(

direction. Fracture conchoidal to

=

2.905; e

=

3.256.

+ ).

Spectral:

0.351 (very large).

Strong, over 0.40.

Dispersion:

zone of copper deposits.

1

Brittle.

Birefringence:

None.

Not diagnostic.

Occurrence:

May

or

0.023-0.040.

Birefringence:

Spectral:

is silicified

those of quartz.

8.09.

Cleavage:

uneven.

Biaxial (— ).

Note:

2-2.5.

Very

Not diagnostic.

Luminescence:

None.

be mixed with copper carbonates such as malachite

and turquoise. Western United States, especially Arizona, New Mexico, Nevada, Utah, Idaho. Mexico; Chile; USSR; Katanga, Zaire; Israel.

Occurrence:

Cinnabar

is

a mineral of low temperature

ore deposits; also in veins, igneous rocks,

and around hot

springs. Crystals are very rare.

Stone Sizes:

Utah; Nevada; California; Texas; Arkansas. Mexico; Peru; Yugoslavia; Italy; Spain; USSR; Germany. Hunan Province, China: source of the world's fin-

eral

est crystals.

Large masses of material, weighing sevpounds, have been found.

COLEMANITE Stone Sizes: Cut cinnabars are extremely small, normally less than 3 carats, and very rare. Some rough exists that might cut up to 50 carats; it is unlikely that fine Chinese crystals that might be transparent would ever be cut since they are extremely valuable as mineral specimens. Cabochons of almost any size up to several inches could be cut from massive cinnabar. DG: 2.68 (red, Mexico).

PC:

22.15, 13.91 (red, China); 19.87 (red pear shape,

Occurrence: High temperature deposits, in metamorphosed rocks, and in vein deposits. Colorado; Idaho; California. Dashkesan, Azerbaijan, USSR; India; Sonora, Mexico; Tunaberg, Sweden; Norway; Germany; Cornwall, England: Western Australia. Cobalt, Ontario: in masses and fine crystals. Massive material would cut stones of any

Stone Sizes: desired size.

China).

Comments:

Faceted cinnabar is extremely rare and only a handful of stones exist. It is cut primarily for collectors and is extremely soft and fragile. This is unfortunate since it is a magnificent red color. Cinnabar carved in China appears regularly on the market, but it is not abundant. Note that cinnabar is used by the Chinese to make a red pigment, which is applied to wood in the form of lacquer, and this

is

the nature of most "cinnabar"

Comments:

The name

very old and lost in antiquity but

is

is

Cabochons

are interesting because of the appearance of this mineral. Cut stones are infrequently seen and are cut only as a curiosity by the collector who wants to have one of everything. lovely reddish metallic

From

Name:

the composition.

COLEMANITE Formula:

carvings sold.

Name:

69

CajBsO,,

5H 0.

•

2

Monoclinic. Crystals are equant.

Crystallography:

pris-

believed to be derived from an Indian word, since India

matic, pseudorhombohedral; massive, cleavable; granu-

was the country of

lar,

origin.

CINNAMON STONE CITRINE

Colors:

Colorless, white, grayish, yellowish white.

Luster:

Vitreous to adamantine.

See: Garnet.

See: Quartz.

CLEAVELANDITE

and as aggregates.

Hardness:

See: Feldspar.

Density:

4.5.

2.42.

Cleavage:

CLINOCHRYSOTILE

See: Serpentine.

CLINOHUMITE

See:

Humite Group.

CLINOZOISITE

See: Epidote.

Perfect

1

direction. Fracture subconchoidal

to uneven. Brittle.

a =

Optics:

Biaxial (+), 2

1.586;

V

Birefringence:

fi

1.592;

y =

1-614.

^ 55°. 0.028.

None.

Pleochroism:

COBALTITE Spectral:

Not diagnostic.

CoAsS.

Formula:

Luminescence: Isometric. Crystals usually cubes

Crystallography:

May fluoresce and phosphoresce

strong

yellowish white or greenish white in SW.

and pyritohedra or combinations of forms; also massive; granular.

Silvery white to reddish, steel gray with a violet

Colors:

tinge; blackish gray.

Occurrence: In saline lake deposits in arid regions. Widespread at localities in California, especially Boron and Death Valley. Argentina;

Streak:

Grayish black.

Luster:

Metallic; opaque.

Stone Sizes:

Density:

Cleavage:

5.5.

Turkey.

Could be

as

much

as 50-100 carats from

large crystals or masses. Crystals are normally

about Hardness:

USSR;

1

6.3.

Comments:

Perfect

1

direction. Fracture uneven. Brittle.

Not diagnostic.

Luminescence:

to

SI: 14.9 (California).

it

Colemanite

is

cut only as a curiosity, since

has no attractive colors. Faceted gems are normally

colorless, have a low dispersion (no fire),

Spectral:

up

inch in size.

None.

and

fragile as well as difficult to cut.

and are

brittle

They have no appeal

except to collectors of the unusual, and material for

70

COPAL

cutting

Name:

Akori coral from Cameroon was highly prized before

potentially abundantly available, since trans-

is

parent material

not extremely rare.

is

the eighteenth century. Similar coral, in shades of red,

After William T. Coleman, owner of the mine

where the mineral was

first

African coast

found.

was found along the South

pink, violet and yellow-orange,

Coral.

The

1978 and marketed as African Star

in

natural coral

is

nonluminiscent, but addition

LW. The and dyed before

of dye produces a bright scarlet fluorescence in

COPAL

See: Amber.

African coral

is

stabilized, bleached,

marketing.

CORAL

Name:

CaC0 (Composed

Formula:

3.

Latin corallium, from the

Gem

CORDIERITE

Calcite.)

Hexagonal

Crystallography:

Greek

korallion.

primarily of the mineral

names:

Iolite;

Water Sapphire.

Dimorph of Indialite.

(R).

(Mg,Feh AUSisOi*.

Formula:

White, flesh pink, pale to deep rose red, salmon pink, red to dark red, blue (rarely), black. May be banded

Crystallography:

or zoned and show a cellular structure.

rectangular cross section; also massive, granular;

Colors:

Orthorhombic. Crystals prismatic with

pseudohexagonal. Note: Indialite Dull to vitreous.

Luster:

Colors:

Hardness:

Blue, bluish violet,

Density:

blue; rarely green-

brown.

2.6-2.7.

Note: Black coral, composed of con-

Vitreous.

Luster: 1.34.

is

Hardness:

None.

Cleavage: Optics:

smoky

3.5-4. ish, gray, yellowish,

chiolin,

maybe

hexagonal.

is

1

.69

2.53-2.78.

Density:

and

.49 (calcite indices) not usually

1

,

meas-

urable. Black coral (conchiolin) has R.I. of 1.56.

7-7.5.

2.57-2.61 (higher

with higher Fe content).

Cleavage: Birefringence:

Most gems are

Distinct

1

direction. Fracture conchoidal.

0.160. Brittle.

Not diagnostic.

Spectral:

a=

Optics:

Luminescence:

Pale violet or dull purplish red.

= Occurrence: Throughout the Mediterranean Sea and Red Sea areas; Southern Ireland; Spain; Mauritius, Malaysia; Japan; Australia; Hawaii; Taiwan. Stone Sizes:

Branches may be several inches to several

feet long but are not always thick. Coral

into beads, cabochons,

is

usually fashioned

and cameos, and

is

also carved.

Large fine carvings of rich-colored material are very rare and costly. Most of the Mediterranean coral is worked in Italy but

much

Conversely, Italy

Comments:

is

is

also sent to

Coral

is

lives in

we know

mm), almost

warm oceans

as coral

is

1.534; y =

1

Dispersion:

y=

1.527-1.578.

.539; birefringence

+ ), 2V = 65-104°. Frequently

optically (-).

0.005-0.018.

Birefringence:

0.017.

Intense and distinctive. Fe-rich crystals:

Pleochroism:

a =

1.524-1.574;

colorless;

y =

violet.

Mg-rich crystals: pale yellow to green/pale blue/violet,

(13-16°C).

Spectral:

Iron spectrum.

Weak bands

at

6451, 5930,

5850, 5350, 4920, 4560, 4360, and 4260. Spectrum observed varies with direction of crystal.

plantlike

The

solid

which these tiny animals live. Coral is often branched and treelike. Japanese coral is pink, white, and red. Hawaii produces black coral. Black and blue corals also come from the coast off Cameroon. The best red coral comes from the Mediterranean. The darkest color is called oxblood and the light pink variety, angel skin. Some black coral is composed of conchiolin, a horny organic material, which looks like coral but is much tougher and less brittle. Large amounts of white, pink, mottled, and oxblood coral from the South China Sea are cut in China and Taiwan. material

(

=

violet-blue.

the axial skeleton of an animal (1

Biaxial

/}

=

for cutting.

also a major buyer of Taiwanese coral.

called the coral polyp, a tiny

animal that

Hong Kong

1.522-1.558;

Lanka: a = 1.530; /J 0.009; S.G. = 2.58).

(Sri

Luminescence:

the colony in

Inclusions:

None (quenched by

Fe).

Crystals of apatite and zircon, the latter

with pleochroic haloes, the outer edges of which are yellow. Frequently dustlike masses of tiny crystals. Also hematite plates in parallel orientation (from Sri Lanka) impart a red color, and gems are sometimes called bloodshot iolite.

deep

Occurrence:

In altered

aluminous rocks; igneous rocks;

alluvial gravels.

California; Idaho;

New

Hampshire.

Wyoming; South Dakota; New York;

CORUNDUM Great Slave Lake, Canada: Greenland; Scotland; England;

Optics:

Norway; Germany; Finland.

1.768).

gemmy material that cuts up to 2 carats. gem iolite in abundance. Lanka and Burma: gemmy material from the gem

o

—

Connecticut;

Uniaxial (— ).

Madras. India:

See

Sri

.757-1 .770; e

Paraiba, Brazil:

some gemmy

material from Virgolandia,

=

1

.765- 1 .779 usually (

1

.760,

table.

Birefringence:

gravels.

in

1

71

Dispersion:

0.008-0.009.

0.018 (low).

nodules.

Pleochroism: Very pronounced. Ruby: strong purplish red/orangy

gem material. Namibia: gem material.

Babati, Tanzania:

Karasburg.

Madagascar; Japan; Australia. Stone Sizes:

red.

Blue sapphire: strong violet-blue/blue-green.

Iolites are frequently in the

1-10 carat

range, dichroic with blue to violet color. Large clean

stones free of inclusions are not

common at all, but gems

Green sapphire: intense green/yellow-green. Orange sapphire: yellow-brown or orange/colorless. Yellow sapphire:

medium

yellow/pale yellow.

over 30 carats have been reported.

Purple sapphire: violet/orange. Brownish orange sapphire: brownish orange/greenish.

BM: worked

Padparadscha: orange-yellow/yellowish orange.

NMC:

crystal

fragment of 177 grams. (Canadian localities).

2.20, 3.93, 2.60

PC:

17.

SI:

15.6, 9.4 (blue, Sri

Lanka); 10.2 (indigo, Sri Lanka).

The crystal structure of cordierite has many

Comments:

dimorph,

similarities to that of beryl; indialite, the

in fact

has the same structure as beryl. Iolite with hematite

comes from

inclusions (bloodshot iolite) inclusions sometimes yield a (quite rare).

The

Sri

gem showing

blue color of

iolite

Lanka. The

a 4-rayed star

along one optical

direction strongly resembles sapphire, and such gems, correctly oriented in settings, are often confused with sapphires. Iolite

not a very rare material, but stones

is

that are completely clean over 10 carats are quite

mon, and clean 15-20 carat gems

are worthy of

uncom-

museum

display.

Lankan ruby fluoresces strong orange-red in LW, pink (moderate) in SW. Sapphire: Blue stones give no reaction, except some blue Thai gems, which fluoresce weak greenish white in SW. Sri Lankan blue sapphire may fluoresce red to orange in LW, light blue in SW. Green gems are inert. Sri Lankan yellow sapphire fluoresces a distinctive apricot color

LW

and X-rays, and weak yellow-orange

fluorescence

Name: studied

Luminescence: The luminescence of corundum is intense and distinctive in identification. Ruby: Burma stones fluoresce intensely, red, in SW, LW, and X-rays. Red fluorescence is, however, not diagnostic of country of origin or natural origin. Thai ruby fluoresces weak red in LW, weak or none in SW. Sri

who

first

ios (violet)

and

After Mr. Cordier, a French geologist its

crystals. Iolite

is

from Greek

lithos (stone).

in

LW

is

weak

in

Hexagonal

Crystallography:

(trigonal). Crystals

mon, often barrel-shaped, prisms with

LW, weaker color strong red in

in

LW,

SW.

LW. LW. Orange: strong orange-red in Some sapphires from Sri Lanka, Montana, and Kashmir glow dull red or yellow-orange in X-rays. Colorless: moderate light red-orange in

(= Ruby, Sapphire)

AI2O3 + Fe,Ti,Cr.

Formula:

light red in

in

SW. The

proportional to depth of color of

gem. Pink sapphire: Strong orange-red SW.

Violet or alexandritelike sapphire:

CORUNDUM

in

flat

com-

ends, some-

purple, orange, yellow, yellow-green, brown, golden amber,

The spectrum of ruby and sapphire can be used diagnostically. Ruby: A distinctive spectrum; a strong red doublet at 6942/6928 is notable, and this may reverse and become fluorescent. Weaker lines at 6680 and 6592. Broad absorption of yellow, green, and violet. Additional lines seen at

peachy pink, pink, and black.

4765, 4750, and, 4685. (The reversible fluorescent dou-

times bipyramidal; also massive, granular, in rolled pebbles.

Colors:

Pinkish red,

medium

to

dark red varieties are

called ruby. All other colors are called sapphire, including colorless, white, gray, blue, blue-green, green, violet,

Spectral:

blet

Luster:

Vitreous to adamantine.

Hardness: Density: Cleavage:

9.

3.99-4.

1

;

usually near 4.0.

None. Fracture conchoidal; frequent parting.

Slightly brittle, usually tough.

is

a sensitive test for the presence of

chromium

in a

corundum. Even mauve and purple sapphires have a trace of Cr and show these lines.) Sapphire: The ferric iron spectrum dominates these stones. In green and blue-green gems, rich in iron, there are lines at 47 10, 4600, and 4500 in the blue-green region. Also lines at 4500 and 4600 may seem to merge and

CORUNDUM

72

become

a broad band.

known

generally

as the

The

three bands described are 4500 complex and are very dis-

tinctive in sapphires. Some blue Sri Lanka sapphires also show a 6935 red fluorescent line and the 4500 line is very weak in these gems. Intermediate sapphire colors are a

metamorphic marbles This

is

weathered away.

Thailand:

The

areas of major importance here are

Chantabun and Battambang. The corundum deposits have only been worked in a major way in modern times.

Gems are found

mixture of the various spectra discussed.

that have largely

the source of the world's finest rubies.

in

a sandy layer within 6 to 20 feet of the

surface and are recovered by washing. Thai rubies are

Corundum

is a mineral of metamorphosed and dolomites, as well as other metamorphic rock types such as gneiss and schist; also in igneous rocks such as granite and nepheline syenite. Gem corundums are often found in placer deposits. Non-gem corundum is abundant throughout the world,

Occurrence:

crystalline limestones

but

gem

material

Burma: Ruby

is

more

restricted in occurrence.

historically

comes from

the

Mogok stone

Gems occur in a gravel layer called byon at a depth of 20 to 100 feet and are recovered by washing and screening with broad screens and then hand-picking encouraging-looking pebbles. Corundum originates in turbulent.

Characteristics of

Cambodia:

Pailin in

Cambodia

is

a source of

the world's finest sapphires, but the country

is

some

not

of

signifi-

cant as a ruby producer.

Kashmir: Fine sapphires occur in northern India in Himalayas at an elevation of nearly 15,000 feet. The deposit is snowed under most of the year. Gems occur in a pegmatite and in the valley below, in surface debris. Kashmir sapphires have a cloudiness due to inclusions and an extremely good blue color, making them greatly the

The history of the mines here is long, complex, and

tract.

important on the current market because of the scarcity Burmese gems.

of

NW

desired, but they are extremely scarce.

Pakistan:

Ruby and

Ruby and Sapphire from Various

spinel of fine quality occur in the

Localities Birefrin-

Sapphire

Australia

gence

S.G.

1.769 1.772 1.772 1.774 1.775 1.772

0.008 0.009 0.009

4.02

1.770 1.770

0.008 0.008-0.009 0.008

3.95-4.05 3.996 4.00

1.761

1.770 1.770 1.769

0.008 0.008 0.008

3.99 3.99-4.02 3.89

.760-1 761 1.762-1.763 1.760

1.770 1.771-1.772 1.768

0.009 0.009 0.008

— — 3.98

1.762

1.770

0.008

3.99

1.769-1.772

0.008 0.008 0.008 0.008-0.009 0.008 0.008-0.009 0.008 0.008

Color

e

blue

1.761

dark blue green

1.763 1.763 1.765 1.767 1.763

Variety

Locality

light

yellow yellow-green golden yellow

Comments

399 4.00 3.97 3.99

0009 0.008 0.008

4.01

Brazil

Jauru, MattoG rosso

Sapphire

dark blue

Ruby

finest red

Sapphire

dark blue

Kashmir Colombia Japan

Sapphire Sapphire

fine blue

Ruby

Malawi

Sapphire

Nepal

Ruby Ruby

purplish-red to pink various red red

Ruby

red

Ruby

red blue yellow

Burma

1.762 1.760-1.769 1.762

1

768-1.778

India

(Taplejung Pakistan

Hunza Sri

1

district]

Valley

Lanka

Sapphire

green Tanzania

Longido

Umba

1.762 1.762

blue, violet

River Valley

Thailand Yugoslavia

Ruby

red

Sapphire Sapphire

orange red -brown

Ruby Ruby Ruby

dark red

red red

1.761-1.763 1.757-1.760 1.760-1.761 1.765-1.770 1.764 1.760-1.763 1.763-1.765 .760-1.764 1.768 1

—

1.765-1 .768 1.768-1 .769 1 .773-1 .779 1.772

1.768-1.772 1.771-1.773 1.768-1.772 1.776

0008

—

-1.765

3.99-4.00 4.00 3.99-4.01 4.00-4.01

399 3.99 3.99-4.06 4.01

4.00

380-3.98

Prilip

= .759-1 .761 o = have higher indices.

Note: Colorless: e

more

iron-rich,

1

;

1

.768-1 769; blue and green: e =

1

.762-1 770; o

=

1

.770-1 779

Among sapphires the green gems,

CORUNDUM Hunza Valley on the Pakistan side of the Kashmir Valley. The color is comparable to Burma ruby but the material Sri

Lanka:

Sri

Lanka

many

a source of

is

sapphire, as well as ruby and star gems. in a gravel layer

known as Mam

at a

colors of

Gems occur here

depth of up to 50 feet.

washed and screened, and gems are is not as good Burma material, and the sapphires are often pale in

The

material

is

recovered by hand-picking. Sri Lanka ruby as

Australia: Anakie, Queensland,

a source of sap-

is

some green gems

phire in blue, green, and yellow shades, as well as ruby. All are in alluvial deposits;

known,

some

fine

gem.

as well as an occasional excellent blue

Other occurrences are noted

in

New South

Wales, espe-

cially the Inverell district (often referred to as the

England

fields).

some

Victoria

Ruby has been found

is

ruby.

a source of fine sapphires

The Umba River Valley

in a

wide range of colors.

of various colors are found,

often zoned with a creamy-white core and blue outer

The

formed and At the Baruta Mine, in Northeast Zimbabwe a deep blue crystal of 3KX) carats was found. Zimbabwe is also a source of black star sapphire. Sapphires from here are not well known on the zone, or vice versa.

up

usually

crystals are well

to 3 inches in diameter.

market.

color but can be very large.

are

is

Zimbabwe: Sapphires

heavily flawed.

is

Province, along with

73

New

a location for green sapphire.

Harts Range, Northern

in the

Malawi: Sapphires were found about 1958 at Chimwadzulu Hill. Kenya: Excellent ruby is known from a small ruby mine. The ruby is pinkish but of fine color and is usually in small sizes.

Afghanistan: Ruby of fine color has come from Jagdalek,

near Kabul. This India:

Territory.

Montana: Yogo Gulch is a well-known locality for fine blue sapphire of very good color that occurs in igneous dikes. The crystals are very flattened and waferlike, so it is difficult to cut large, full-cut gems from them. Crystals occur in many different colors and are usually quite

an ancient source of many of the fine

is

stones of ancient times.

Mysore produces poor quality rubies but a amount of star ruby. Some of the stones from

significant

common. The Matto Grosso area has produced sapphires. Gem corundum is occasionally found in Norway; Finland; Greenland; USSR; Czechoslovakia; Pakistan; Nepal. this

area are of excellent quality but are not

Brazil:

small, but the blue stones are extremely fine. This material is

often zoned and

luster.

Ruby

is

may have

uncommon

a curious metalliclike

here.

,

blues are

also exists.

somewhat

The

pale;

some

asteriated material

stones are rich in iron and poor in

titanium. Metallic rutile crystal inclusions are typical.

Japan: Transparent crystals to 5 zoisite

rock on Mt. Gongen,

cm

Hodono

amphibole-

in

Valley,

Ehime

Scotland: Blue sapphire crystals (cuttable) up to about

mm in diameter have been found at Loch Roag, Isle of

Lewis, Outer Hebrides. Colors are variable, sector zoning observed. Paragenesis similar to that of Pailin,

Cambodia. Cut stones are small (maximum 2-3 Tanzania: Large ruby of fine color and quality in

green, massive chromiferous zoisite.

usually opaque,

and the rock

as a

enough

The

whole

decorative material, but occasionally of this ruby are transparent

and Australian

orthoclase, niobite, columbite, calcite, monazite,

carats). is

crystals are is

cut as a

some small

to facet.

found

areas

Many colors

of sapphire are found in the vicinity of Morogoro, Tanga

zir-

con, apatite, fergusonite, and thorite. Tanzanian sapphires contain crystals of chlorapatite, pyrite, magnetite,

and Matto Grosso): rounded

biotite, graphite, phlogopite, zircon,

Brazil (Jauru,

spinel. gas-filled discs

that resemble bubbles.

Burma (Mogok): silk

short rutile needles at 60° angles;

consisting of hollow tubes plus crystals of rutile,

spinel, calcite, mica, garnet; zircon crystals with haloes;

color swirls

known

as treacle.

Thailand: feathers

—

canals and tubelike liquid inclu-

brownish cavities; twin planes; crystals of niobite, almandine, apatite, pyrrhotite; plagioclase crys-

sions; flat,

sapphires. Rutile

tals in

Sri

Lanka: long

is

absent.

rutile needles; healing cracks; zircon

crystals with haloes; flakes of biotite

and phlogopite

mica; feathers with irregular liquid hoses inside; color

zoning

Prefecture.

45

In general, Burmese, Thai,

blue sapphires contain crystals of plagioclase feldspars,

North Carolina: At Cowee Creek, in Macon County, small rubies and sapphires are found in stream gravels and soil. The quality is usually poor, but an occasional fine, small ruby is found. Namibia: At Namaqualand opaque ruby is found that is suitable for cabochons. Colombia: Blue and violet sapphires, many showing a distinct color change, are being mined near Mercaderes, Cauca, Colombia, probably originating in alkalic basalts. Crystals are prismatic and rounded, up to 3 cm in size. Colors are typically blue, green-brown and violetish, but some yellow, pink, and red crystals have also been found.

The

Inclusions:

is

frequent; crystals of spinel, graphite, ilmenite,

apatite.

Pakistan (Hunza Valley): phlogopite; chlorite; monazite; spinel; rutile;

magnetite; pyrite, calcite.

Cambodia (Pailin): specks of uranian pyrochlore (ruby red color, very small).

Kashmir: yellow and brown feathers and thin films; 60° and 120°; cloudy haziness; negative crystals, flat films; rods and tubes. Tanzania (Umba River Valley): apatite; graphite; liquid-filled canals; veil-like lines at

pyrrhotite.

Tanzania (Longido): pargasite, spinel,

zoisite.

CORUNDUM

74

Australia: Discoloration and twin lamellae; rutile crystals; liquid-filled feathers, flat cavities;

color zoning

is

frequent.

Nepal: Undulating

strong color zoning, pris-

veils,

matic crystals, margarite.

Natural History Museum, Paris:

Malawi (Chimwadzulu Hill): fine tubes; small black and short rods; healed fissures; color zoning.

(

stone from this locality.

Diamond Fund, Moscow: 258.8 (blue), fine, lively gem.

ROM: do

size than

Sapphires, in general, reach a far greater rubies.

whereas sapphires

A

in

ruby of 30 carats

a great rarity,

is

museum collections weighing hununcommon. The largest rubies

dreds of carats are not

come from

the chrome-zoisite matrix in Tanzania, but

these are not really of large size

occur

gem

in the Sri

quality. Fine

Lankan

gem

on the

is

cur-

Ruby:

Crown Jewels of England: Edwardes Ruby, 167

carats.

-Guy, Prague: 250 carats.

BM:

ruby crystal of 690 grams (Burma).

Burmese rough

and 45 carat gems. A rough of 304 carats was found about 1890. Also famous are the Chhatrapati Manick and the 43-carat Peace Ruby.

Crown

up

Jewels: fine buckle of 84

(violet-red star

Burma ruby

Reeves star ruby (red, Sri Lanka); 50.3 ruby, Sri Lanka); 33.8 (red star, Sri

Lanka).

LA: Burma

of 119 carats. Also

-75

carats.

Ruby

Comments:

is the most valuable of all gemstones, one of the most popular. Despite the enormous size of these gems as seen in museum and Royal collections, corundums available on the market are usually of more modest size. A 3-4 carat ruby, if of fine quality, is a rare and very expensive gem today. Sapphires of good blue color over 5 carats, if clean, are similarly rare and also valuable. There is an abundance of good quality small sapphires but not of rubies.

and sapphire

is

corundum

is

created by the inclusion of rutile

corundum

needles provide a chatoyancy.

crystal.

The

rutile

into a

cabochon the sheen

is

reflections

from these

When such material is cut

concentrated along the top 1 20° angles,

of the stone into three white lines crossing at

creating a six-rayed

star.

Very rarely there are two disaccording to the first and

tinct sets of needles oriented

second order prisms of the corundum (30° apart), resulting

Lanka, "Logan sapphire"); 330 (blue 316 (blue, Sri Lanka, "Star of Artaban"); 98.6 (deep blue, "Bismarck sapphire"); 92.6 (yellow, Burma); 67 (black star, Thailand); 62

Burma,

in a strong, 12-rayed star.

Next to diamond, corundum is the hardest mineral known and is very compact and dense, with no cleavage. As a result, corundum is one of the best of all jewelry stones, especially star

423 (blue

(black

gem

oval, nearly clean,

crystal 196.1 carats.

Sapphire:

star,

Kashmir blue

fine

to 11 carat size.

SI: 138.7 Rosser

SI:

Hollow rectangular cabochon

symmetry of the corundum, and

that yielded 70

cabs,

Crown Jewels:

of 191.6 carats; oval, yellow

needles orient themselves according to the hexagonal

PC-

Iranian

Iranian

needles within the host

100 (de Long star ruby).

Historical rubies include a 400 carat

Thailand).

Star

Narodni Museum, Prague: 27.11 (Burma).

AMNH:

Burma, in 1929, saw 951 carat sapwhich may be the largest ever found there. AMNH: 536 (blue, "Star of India"); 116 (blue, "MidBritish mission to

phire,

night Star"); 100 (yellow, Sri Lanka); 100 (padparadscha,

a fine ruby over 3-4 carats

St.

Lanka); 43.95 (greenish yellow, Sri Lanka);

very fine, Sri Lanka); 163 (blue, Sri Lanka); 34 (violet,

rent market.

Cathedrale

Sri

193.3 (blue star sapphire).

rubies of

range. In general, a fine blue sapphire over 5-10 carats is

179.4 (golden yellow, Sri Lanka); 28.6 (pad-

paradscha,

gravels, with smaller

ones from Burma and Thailand. Enormous sapphires of fine color and transparency have been found in the gem gravels of Sri Lanka and Burma, but most are from Sri Lanka. A 1400-gram ruby was found in Yugoslavia (Prilip) but was not gemmy. Malawi material reaches a size of about 12 carats (sapphire). Large sapphires have been found in Australia; Montana sapphires over 1 carat are very rare, but the blue ones are magnificent in this size very rare, as

Raspoli, 135 carat

sapphire, cushion-cut, 12.54 carats, believed largest

crystals

Stone Sizes:

le

brown, lozenge-shaped rough, clean. Tested by GIA: 5600 carat sapphire cabochon; also Mysore India) ruby cab of 1795 carats; Montana blue

Sri

"star of Asia");

star, Australia);

42.2 (purple, Sri Lanka); 35.4

(yellow-brown, Sri Lanka); 31 (orange, Sri Lanka); 25.3 (colorless, Sri Lanka); 19.9 (pink, Sri Lanka); 16.8 (green, Burma).

PC: Black Star of Queensland,

oval,

carats, world's largest black star.

A

found

in 1948,

733

yellow crystal of

217.5 carats was found in Queensland in 1946.

corundum, which is tough as well gems are slightly brittle and

as scratch-resistant. Faceted

can be chipped, though much less easily than other gems. Very few ruby deposits are known that can be actively worked, which creates ever greater strain on ruby supply in the marketplace. Many more sapphire deposits are

in

operation, so the situation here

is

not as

critical.

Name: Corundum is from the Sanskrit word kurivinda. Ruby and sapphire come from the Latin words meaning red and blue, respectively. Padparadscha

word meaning

lotus blossom.

is

a Sinhalese

CROCOITE COVELLITE Formula:

Biaxial (-), 2

CuS. Hexagonal. Crystals are tabular; also

Crystallography:

massive and cleavages.

and

iridescent, yellow

commonly

1.461;

Shining gray-black.

Luster:

Submetallic to resinous; opaque, except

in thin

y =

1.485.

Moderate.

Not diagnostic.

Spectral:

Luminescence:

Medium

bright white to

cream (LW).

white to cream color (SW);

Occurrence: Colquiri, Bolivia.

Hardness:

1.5-2.

Creede, Colorado: Density:

4.68.

Thin sheets

Brittle.

o

Optics:

=

Wagon Wheel Gap, Colorado: 1

direction. Facture uneven.

1.45.

Occurrence:

None.

Secondary enrichment zones of copper

mines.

Montana; Wyoming; South Dakota; Colorado;

Utah; California; Alaska. Sardinia, Italy; Argentina;

New

Zealand; Philippines;

Australia; Yugoslavia.

Cabochons are generally cut from massive material. The stones can be very large, up to

Stone Sizes:

PC: 0.96

Comments: Covellite is cut strictly as a collector curiosity. Cut gems have no great value, but the blue or iridescent colors can be very attractive. Covellite

too soft to wear and difficult to cut —

it

is

much

who discovered

the mineral on

Italy.

CREEDITE Ca Al2(SO 4 )(F,OH), 1

Name:

Occurrence

less

than

•

2H

2

in the

Creede Quadrangle, Colorado.

See: Quartz.

CROCOITE Formula:

PbCrO*. Monoclinic. Crystals prismatic, some-

times hollow. Colors:

Red-orange, cherry red, orange, yellowish.

Streak:

Orange-yellow.

Luster:

Adamantine

0.

Hardness: Crystallography:

to vitreous.

2.5-3.

Monoclinic. Crystals short, prismatic; Density:

also radial clusters.

Colors:

Colorless, white, rose to lilac or purple.

Cleavage:

Luster:

Vitreous.

Optics: Biaxial

5.9-6.1.

Indistinct. Brittle.

a = 2.29-2.31 (+),2V= 57°.

;

/J

=

2.36;

y=

2.66.

4.

Birefringence:

Cleavage:

1

gem.

Crystallography:

After N. Covelli

Density:

to

Comments: Creedite is one of the very rare minerals known to collectors. It may well be that less than a dozen creedite gems have ever been cut. The mineral itself is rare, cuttable crystals even more so. These would be colorless or purple and from the Mexican occurrence. The hardness is too low for wear— strictly a collector

can be scratched

with a fingernail!

Hardness:

up

(purple, Chihuahua).

CRISTOBALITE

several inches long.

Formula:

in crystals

Faceted gems very small, usually

Stone Sizes:

Strong, but visible only in very thin sheets.

Luminescence:

Mt. Vesuvius,

a fluorite-barite mine.

1-2 carats.

Pleochroism:

Name:

in

gemmy.

inch long,

(

or foliated

rock with fluorite and

Santa Eulalia, Chihuahua, Mexico:

flexible.

Uniaxial + ).

Germany;

in cavities in

barite.

Perfect and easy

Cleavage:

Brittle.

1.478;

Darwin, California; Granite, Nevada.

slivers.

Butte,

=

0.024.

red.

Streak:

j)

V= 64°.

Birefringence:

Dispersion:

Light to dark indigo blue; purplish;

Colors:

a =

Optics:

75

0.270.

2.71-2.73.

Perfect

1

direction. Fracture conchoidal.

Dispersion:

Pleochroism:

Strong.

Orange-red to blood red.

CRYOLITE

76

band

Distinct

Spectral:

at

fragments. Transmits mainly

5550 but seen only in

in thin

the yellow-red region of

the spectrum.

Luminescence: Weak reddish weaker effect in LW.

to

in

oxidized zones of

lead deposits.

Dundas, Tasmania: best crystals found

some gemmy; Beresov Tiger,

in the

world,

large clusters.

USSR: red

District,

Minas Gerais,

Gems

Stone Sizes:

Comments:

Cut

cryolite

birefringence,

is

The

is

somewhat

translucent,

and

cuttable material has a very low

colorless,

and very

soft

— not exactly an

exciting-looking gem. However, there are very few cut

stones in existence because of the extreme scarcity of suitable rough. In addition, cryolite

abundantly

at

is

one

locality (Ivigtut).

the

Greek kryos (frost) and

only found

crystals.

Name:

Arizona: very tiny crystals.

California:

abundant material

has a "sleepy" look.

Secondary mineral

Occurrence:

dark brown (SW);

Large cabochons could be cut from the in Greenland. Facetable material is quite rare, however, and only tiny gems can be obtained. Stone Sizes:

hence

Brazil.

can be up to about 10 carats, but

From

ice-stone, in allusion to

CRYSTAL

its

lithos (stone),

appearance.

See: Quartz.

these are usually not transparent. Clean stones up to 1-2

carats are available in

deep red-orange color from

Tasmania.

DG:

CUPRITE Formula:

CU2O.

14.5 (orange, Tasmania).

Comments:

one of the loveliest of all collector stones. It's too soft and brittle for wear, but it is quite a rare mineral and relatively few stones have been cut. The dispersion is high but completely masked by the intense body color. Crocoite

From

Name:

the

is

Greek krokos, meaning

octahedra, or combinations; also needlelike,

in densely packed mats called chalcotrichite with no gem significance.

Colors:

Brownish red, red, purplish red, nearly black.

Streak:

Brownish

Luster:

Adamantine

Hardness: Density:

CRYOLITE 3

AlF6.

Optics:

Monoclinic. Crystals cuboidal and

Crystallography:

6.14;

pris-

N=

Sometimes anomalously pleochroic.

Pleochroism:

Luminescence:

None.

Occurrence: Secondary mineral in copper deposits. Usually microscopic crystals. Arizona; New Mexico; Pennsylvania; Colorado; Utah;

to black.

Vitreous to greasy.

Hardness:

6.0-6.07.

2.848.

Colorless, white, brownish, reddish; rarely gray

Luster:

Namibia =

Poor. Fracture conchoidal to uneven. Brittle.

matic; usually massive. Colors:

to submetallic; earthy.

3.5-4.

Cleavage:

Na

red.

saffron, in

allusion to the color.

Formula:

Isometric. Crystals, cubes, and

Crystallography:

SI: 5.7 (orange-red, Tasmania).

Idaho.

2.5.

Mexico; Bolivia; Chile; France; USSR; Zaire; Japan;

Density:

2.97.

other locations.

None. Fracture uneven.

Cleavage:

a =

Optics: Biaxial

(

1.338;

+ ),2V=

-

1.338;

y =

43°.

Not diagnostic.

Luminescence: Occurrence:

Stone Size:

Largest mass of cuttable cuprite (PC)

is

completely transparent and weighs 2 kg. Before the amazlargest stones were less than 1 had ever been found. Onganja stones have been cut up to 300 carats, are flawless, and

ing

Onganja discovery, the

potentially could be

None observed.

Occurs

transparent;

often coated with green malachite.

carat, as only tiny crystals

None.

Pleochroism:

more than 6 inches across, blood red and

1.339.

0.024 (approximately).

Dispersion:

Onganja, Namibia: unique occurrence, with crystals up to

0.001; almost isotropic.

Birefringence:

Spectral:

/?

Brittle.

in alkalic

rocks at Ivigtut, Green-

much

larger.

SI: 203.75 (octagon, Namibia);

Namibia).

ROM:

66.34 (oval, Namibia).

land.

PC: 299.5

Also Spain; USSR; Colorado (small amounts).

DG:

(oval,

Namibia).

48.6 (red, Namibia).

172, 125.5, 110 (red,

CYPRINE Comments: all

Cuprite

is

one of the

rarest of all

practical purposes, cuttable material

gems. For

comes from

only one locality. Only good crystals or pieces of crystals are cuttable, however, as other material

from

this

mine

is

opaque. Mineral collectors do not wish to see their fine crystals cut, limiting the supply of available faceting material. Cut gems have a metallic appearance and mag-

nificent

77

deep red color. There are unwearable, but among all gems and someday may be

the most beautiful of

extremely rare

in

Name:

the Latin

From

the marketplace.

cuprum

the composition.

CYPRINE

See: Idocrase.

(copper), in allusion to

D

DANBURITE Formula:

Madagascar: yellow crystals

USSR:

CaE^SizOs.

is

wedge-shaped terminations,

gemmy

Danburite

Stone Sizes:

Orthorhombic. Crystals prismatic with

Crystallography:

colorless,

at

Mt.

Bity, often

is

not a very rare mineral, but

scarce in large facetable pieces.

The

usual range

like topaz.

carats, especially for colorless material

The yellow Burmese gems

Colorless, white, pink, light to dark yellow,

Colors:

is

it

1-5

from Mexico.

are rare today, especially in

the 7-10 carat range.

yellowish brown, brown.

BM: Burma gem,

Vitreous to greasy.

Luster:

gemmy.

material.

step-cut, flawless, wine-yellow color,

138.61 carats.

Hardness:

PC: 20 (Burma, peach color); 22.76

7.

(yellow,

Madagascar);

37 (USSR). 2.97-3.03 usually 3.00.

Density:

SI: 18.4 (yellow,

Cleavage:

Indistinct. Fracture

subconchoidal to uneven.

a=

Biaxial (-); at

12.4, 10.5 (colorless,

LA: 115 (brownish emerald

Brittle.

Optics:

Burma)

1.630-1.633;/?

2V =

88°

in

-

1.633-1.637;

y=

ROM:

1.636-1.641.

red to green light; optically

(

+

Dispersion:

Pleochroism:

sufficient material exists to allow almost every collector

0.017.

to have a colorless

None.

Sometimes shows rare earth spectrum

didymium

lines.

Name: ,

gem.

After the type locality, Danbury, Connecticut.

so-called

Luminescence: Sky blue to bright blue-green Also thermoluminescent (red). Occurrence:

USSR).

Danburite is a hard and durable stone with poor cleavage— an excellent choice for wear. The dispersion is quite low, so gems have no fire but are very bright when properly cut. Large ones are very rare, but

0.006-0.008.

Spectral :

cut, Madagascar).

12.72 (colorless step cut,

Comments:

)

lower wavelengths.

Birefringence:

Mexico);

7.9 (colorless, Japan).

in

DATOLITE

LW.

CaBSiO^OH).

Formula:

In dolomites; in carbonate veins in granitic

Crystallography:

Monoclinic. Crystals prismatic or

rocks.

stubby; massive, granular.

Danbury, Connecticut: type locality. Charcas, San Luis Potosi, Mexico: colorless, yellow, light pink (gemmy). Mogok. Burma: yellow and colorless, sometimes large

Colors:

Colorless, white, pale yellow, green, also pink,

reddish, and brownish ties

due to impurities; massive variecan be white to orange-brown or pink.

crystals (rolled pebbles).

Obira, Bungo, Kyushu, Japan: colorless crystals,

Luster:

some-

times gemmy.

Vitreous.

Hardness:

78

5-5.5.

DIAMOND Density:

None; fracture uneven toconchoidal;

a=

Optics:

1.622-1.626;

(-),2V=

Biaxial

excellent books on these topics are listed in the Bibliog-

2.8-3.0.

Cleavage:

=

/3

1.649-1.658;

y=

raphy on page 237. brittle.

1.666-1.670.

C

Formula:

(carbon).

Essentially pure with only

75°.

minor traces of impurities.

Isometric. Crystals sometimes sharp

Crystallography:

0.044-0.047.

Birefringence:

79

octahedra, dodecahedra, and combinations with other Dispersion:

forms. Crystals modified, often rounded and distinguished

0.016.

by the presence of triangular-shaped

None.

Pleochroism:

pits

on octahedral

faces (once believed to be due to etching, these "trigons"

Not diagnostic.

Spectral:

Luminescence:

Blue

are currently believed to be a result of the growth process).

SW (attributed to the presence

in

of Eu).

Colorless, gray, shades of yellow, brown, pink,

Colors:

green, orange, lavender, blue, black; rarely red.

A secondary mineral in basic igneous rocks

Occurrence:

Adamantine.

Luster:

and traprocks. Massachusetts; Lane's Quarry,

Springfield,

Massachusetts; Paterson, ties in

New Jersey

Westfield.

(and other

locali-

the state).

Faraday Mine, Ontario, Canada: colorless material. Tyrol, Austria; Habach, Austria; Cornwall, England. Lake Superior Copper district, Michigan: nodules of

Hardness:

10.

Diamond

is

the hardest natural substance

any other mineral. The difference in hardness between diamond and corundum (9) is very much greater than that between any other two minerals

and

easily scratches

on the Mohs Density:

scale.

3.515;

Carbonado

2.9-3.5.

massive datolite. Cleavage:

Brown or white massive

Stone Sizes:

material will cut

cabochons up to several ounces. The colors in the Michigan material are due to copper staining. Cabochons are seldom seen in collections— collectors prefer to polish the faces of sliced-open nodules. These can be up to about 6 inches in diameter. The best faceting material comes from Massachusetts, with fine pale green material from New Jersey. The largest gems cut from this are in the 5-carat range. Larger stones are very rare. SI: 5.4

HU:

and

5.0 (colorless, Massachusetts).

spite of

Perfect

its

1

direction (octahedral). Brittle. In

great hardness,

diamond can be

along octahedral planes. This feature since cleaving a large

sawing.

monds

The to be

Optics:

diamond saves weeks

cleavage also makes

chipped

in

it

split easily

useful in cutting,

is

of laborious

possible for dia-

wear.

Isotropic, index very constant; TV

=

2.417.

0.044. This high dispersion in a colorless

Dispersion:

diamond creates the

"fire" that

the source of the

is

diamond's attractiveness.

13.21 (flawless triangle, Massachusetts).

NMC:

Pleochroism:

0.45 (colorless, Canada).

Comments: considered.

Datolite

is

a rather soft gemstone

The nodules come

Faceted stones are extremely persion

(fire) is low.

if

wear

is

in very attractive colors.

brilliant,

though their

Most faceted gems

dis-

are colorless,

pale yellowish or pale green.

Name:

From

a

Greek word meaning

to divide

because

See: Garnet.

DIAMOND is the best known gemstone. Its history of use and great value extends thousands of years into the past. Diamond has been the center of intrigue, warfare, romance, and tradition on a scale unequaled by any other gem. The history and lore of diamonds, diamond technology, and cutting are subjects so vast in themselves that they are far beyond the scope of this book. Several

Diamond

The absorption

diamonds are quite

spectra of various colored

distinctive

and

useful, especially in

diamond from natural The colored diamonds can be grouped

distinguishing irradiation-colored

colored stones.

into several series:

of the granular nature of the massive variety.

DEMANTOID

Spectral:

None.

Cape

Series: Colorless to yellow

diamonds

that fluo-

resce blue. Strong lines at 4155, 4785, 4650, 4520, 4350,

and 4230. Most

lines are

hard to see.

Brown Series: Brown, green, and greenish yellow monds that fluoresce green. Strong line at 5040 weak lines at 5320 and 4980.

dia-

plus

Yellow Series: Colorless, brownish yellow or yellow and yellow-fluorescing. This series includes the true "canary"

No discrete spectrum

yellow diamonds.

weak

but sometimes a

line at 4155.

Type 1TB Blue: No absorption spectrum. Pink diamonds show the so-called "cape" absorption line at 4150 and a broad, diffuse band centered at 5500. The strength of this

band correlates with the

color of the diamond.

intensity of

DIAMOND

80

Many diamonds

Luminescence: let,

fluoresce blue to vio-

with fluorescence sometimes in zones (often a result

The

sometimes strong enough to be visible in daylight. Yellow stones sometimes fluoresce yellow-green. Some pink diamonds from India fluoresce and phosphoresce orange. The famous Hope diamond, deep blue in color, phosphoresces deep red. Most fluorescence occurs in LW; the SW reaction is weaker and the same as LW. Many diamonds fluoresce bluish white in SW. Blue-fluorescing diamonds may phosphoresce yellow (an "afterglow" reaction). The various diamonds have been organized into types, with varying UV of twinning).

effect

is

transparency.

Type

Transparent to

I:

3000 A;

this

all

down

wavelengths

type contains nitrogen and

is

to

about

further subdivided

Types la and lb. Type la represents the majority of diamond, and the nitrogen is in the form of platelets. About 0. 1 % of Type I diamonds are Type lb, in which the into

all

dispersed throughout the crystal.

nitrogen

is

Type

Transparent

II:

all

contains aluminum. Type

the

way

Ha does

to

2250 A;

this

type

not phosphoresce in

SW

and contains little nitrogen. Type lib has bluish phosphorescence in SW and is also electrically conductive.

Nitrogen

these

diamonds is absent or very scarce.

Diamond

Inclusions: tals of

in

crystals frequently contain crys-

other minerals.

Olivine

may

look

like

bubbles (rounded

crystals), pres-

ent in single crystals or clusters, often on octahedral faces and aligned parallel to octahedral edges.

These are

pale green or colorless.

Garnet

is

present in single crystals or clusters; brown,

lilac, and purple colors have been observed. These are usually pyrope garnets

orange, yellow, pink, violet-red,

and sometimes reach large size. They are seen frequently in South African diamonds. Graphite

is

present as black inclusions.

Pyrrhotite, pyrite, pentlandite, ilmenite,

colored ore minerals) these are typical of

Diamond

and

rutile (dark-

may resemble graphite

inclusions;

diamond from Ghana.

crystals are often seen as inclusions in other

diamonds, usually

in perfect crystal

forms.

Chrome diopside is present as emerald-green, well-formed crystals. Also seen in South African diamonds is chrome enstatite.

Chrome

spinel in octahedra, sometimes distorted, usu-

reddish-brown or black; these are Russian diamonds. ally

Ruby has

also

been observed

in

commonly seen

in

an eclogitic diamond.

Cloudlike inclusions are sometimes in the shape of a Maltese cross, and are diagnostic of diamonds from India.

Occurrence: Diamond is a mineral formed at very high temperatures and pressures, deep within the earth. Synthetic diamond is produced at pressures as high as 100,000

atmospheres (equivalent to 200 miles of rock!) and temperatures around 5000°C these conditions may approximate those of natural diamond formation. Diamond formed at depth is apparently "exploded" to the surface in fissures that become circular near the surface and are known as "pipes." The mineralogy of the rocks in these pipes, known as kimberlite, is unusual and unique and reflects high pressure of formation. Diamond is found in kimberlites and also in alluvial deposits (streams, river channels, beaches, deltas, and former stream beds) derived from kimberlite weathering and erosion. South Africa: Diamonds were first discovered on the shores of the Orange River. After several "rushes," abundant "diamond fever," and a turbulent period of changing ownership, nearly all the deposits were under control of De Beers Consolidated Mines, Ltd, by 1888. De Beers is now part of Anglo American, a huge conglomerate that also owns the rich gold mines of the Rand in South Africa. South African diamonds are among the world's most famous, and such mines as Premier, Jagersfontein, Bultfontein, Dutoitspan, and Wesselton are famous for their output. South Africa is still a world leader in dia;

mond

production, but large stones are becoming very

scarce.

Other African countries: Diamonds are found in many Zimbabwe is noted for alluvial deposits. The huge production of very fine stones from Angola has been interrupted by political problems. Ghana produces diamond from gravel beds, mostly industrial; some are gem quality. The Ivory Coast and Republic of Guinea produce alluvial diamonds. A large deposit is known in Namibia where the Orange River enters the Atlantic Ocean. Huge machines work enormous beach deposits in Namaqualand, and other spots along this coast. Central African Republic produces diamonds associated with gravel beds. Alluvial diamonds occur in Zaire and especially in Sierra Leone. The Sierra Leone diamonds are among the world's finest. They occur in river gravels, are often very large, and are of top gem quality. Occasional stones are found in Tanzania: John Williamson found a large pipe in 1935, and some fine diamond has been recovered from this deposit. Other African sources include Lesotho and Botswana. India: The first major historical source of diamonds, and also the source of many of the largest and most famous gems (including the Hope diamond). Mines are in Golconda, Andhra Pradesh (Hyderabad), Kollur, and other localities. Indian diamonds are primarily alluvial, found in sandstones and conglomerates or gravel deposits. Brazil: Produces a large quantity of diamond, but little of good gem quality. The Diamantina district was opened in 1725, and diamond also comes from Bahia, Minas Gerais, Matto Grosso, and other states. Diamond in Brazil occurs in a variety of rock types and also parts of Africa.

alluvial deposits.

Most of

the stones are small in size but

an occasional large, fine gemstone

is

found. Bahia pro-

DIASPORE duces black microcrystalline diamond known as carbonado. The largest of these found weighed 3078 carats. Borneo and Indonesia: Small alluvial deposits. Most stones are small (less than 1 carat). Diamonds from Borneo have been reported to be harder than those from other deposits.

Venezuela:

A

substantial alluvial production, mostly

1893), the Star of Sierra

81

Leone (968.8 carats, white. Mogul (787.5 carats,

Sierra Leone, 1972), and the Great

A fine yellowish octahedron of 616 on display at the Mine Museum in Kimberley, South Africa, found in 1975. The world's largest uncut diamond, an 890 carat "fancy

white, India, 1650). carats

is

intense golden yellow"

African

is

owned by

the Zale Corp.

The

but from an undisclosed source.

of small, yellowish crystals.

stone

USSR: Russia is one of the leading world suppliers of diamonds. The country is rich in pipes (several hundred have been found), some of very large size (such as the famous "Mir" pipe). However, most Russian diamonds are very small, severely limiting the value of the production. A high percentage of crystals is of good color and transparency, and the production is substantial enough to be a major factor in the world diamond market. All the pipes are located in Siberia, where weather conditions make mining both difficult and expensive. Australia: As long ago as 1972 it was realized that the geology of northwestern Australia was strikingly similar to that of South Africa's diamond region. A group called the Ashton Joint Venture Partners started to explore this region and found kimberlite pipes in 1976. A diamondiferous pipe was then found at Ellendale in 1977 and a rich field of alluvial diamonds at Smoke Creek in 1979. An immense pipe known as AK-1, south of Lake Argyle, is being developed; this pipe is complex with an elongated

If cut, it could yield a finished stone of 600 carats, which would then become the world's largest polished diamond. The Zale diamond is the fourth largest rough ever

surface outcrop.

AKT

,

discovered

in 1979,

than 100 million tons of kimberlite,

contains more

much

unusually high grade of 7 carats per ton.

It

of

it

with an

was estimated

Smoky Creek plus AK-1 could add as much as 50% to the world's known diamond reserves. However, Argyle that

diamonds tend

and low

(5% gem, South African diamond will therefore continue to dominate the world gemstone market. However, Australia (in carat production) is expected to become the world's largest diamond to be small

40% low-grade gem, 55%

is

in origin,

found.

The largest cut stones include: Cullinan I (530.2, white, in the British Crown Jewels), Cullinan II (317.4, white, cushion, British Crown Jewels), Great Mogul (280.0, white, dome-shape, location unknown), Nizam pear shape,

(277.0, white, table-cut,

was

in India in 1934), Jubilee

(245.35, white, cushion, privately

owned,

Orloff 189.6, white, rose-cut, Russian

Paris),

and the

Diamond Fund

in

the Kremlin).

Diamond

Comments:

heavily marketed of

all

the most romanticized and

is

gemstones. Nearly every jewelry

establishment handles diamonds, even if it has no other gemstones in stock. The annual world production of diamonds is on the order of 10 tons. Of course, only a small percentage of this

very fine quality

is

is

gem

quality, but

nowhere near as scarce

diamond

of

as equivalently

high quality ruby or emerald.

From

Name: hardest

steel,

the Greek word adamas, meaning the and hence the hardest gemstone.

in quality

industrial).

producer.

DIASPORE

Dimorph o/Boehmite.

AIO(OH) + Mn.

Formula:

Orthorhombic; crystals are elongated

Crystallography:

plates, acicular needles; also massive, foliated.

United States: The only significant diamond deposit North America is at Murfreesboro, Arkansas. This is a very large pipe, which has never been systematically developed and might be extremely rich. It is on governmentowned land and has been worked surficially only by tourists who pay a small fee for the privilege of digging. The largest crystal found here weighed 40.23 carats and was named the "Uncle Sam" diamond. Alluvial diamonds have been found throughout the United States, presumably carried south by waters flowing from Canadian glaciers thousands of years ago. The Canadian source pipes have never been discovered, however. Large diamonds found in Virginia include the "Dewey" (1885, 23.75 carats) and the "Punch Jones" (34.46 carats). in

Colors:

Colorless, white, yellowish, pink, rose red to

dark red (due to Mn), Luster:

greenish, brownish.

Vitreous; pearly on cleavage.

Hardness:

6.5-7.

3.3-3.5; Turkish material 3.39.

Density:

Cleavage: Optics:

lilac,

Perfect

a =

Biaxial (+),

Pleochroism:

direction. Fracture conchoidal.

1.702;

2V =

Birefringence:

1

y =

=

1.722;

in

manganiferous variety:

1.750.

85°.

0.048.

Strong

violet-

blue/pale green/rose to dark red.

Stone Sizes:

The

largest

rough diamonds ever found

include the Cullinan (3106 carats, white. South Africa.

Spectral:

1905); the Excelsior (995.2 carats, white. South Africa,

bands

at

Not diagnostic; Turkish stones show broad 4710, 4630, 4540. and a sharp line at 7010.

DICKINSONITE

82

Luminescence:

Dull pale yellow in

SW

(Chester, Mas-

Birefringence:

Dispersion:

Occurrence: In metamorphosed limestones, chloritic schists, and altered igneous rocks. Also in bauxite deposits. Mamaris, Yagatan, Mugla Province, Turkey: gemmy, pale-

brown

some fragments

corundum in emery deposit;

cuttable.

to 2 inches long

and k inch x

thick, colorless to

brown;

cuttable.

Pale olive green to pale yellowish green.

Not diagnostic.

Spectral:

Diaspore crystals from Massachusetts were,

Stone Sizes:

when found, apparently suitable for cutting, and a few gems may have been cut from the Pennsylvania material. However, cut disapore was, at best, an extremely unlikely gemstone until the find of crystals in Turkey. This locality has produced the vast majority of cut diaspore now in existence. Moreover, the locality produced cuttable pieces enormously larger than had ever been known previously mineral.

PC: some of the

(light

brown,

oval); 10.63 (light brown).

hard enough to make a durable jewelry stone, but the typical light brownish color is not easy to sell. Despite the large Turkish material, this is Diaspore

is

From

because

it

secondary phosphate mineral

in gran-

Branchville, Connecticut; Portland, Connecticut; Poland,

the

falls

Very tiny green gems, less than 1-2 carats, have been cut from Connecticut material. Stone Sizes:

Comments:

is seldom even mentioned in because it is so rare and has been so seldom cut. Faceted gems are practically nonexistent, and would be among the rarest of all cut stones.

the

gem

Name:

This mineral

literature

After the Rev. William Dickinson in recogni-

tion of his interest in the locality

DINOSAUR BONE

where

first

found.

See: Quartz.

Greek

DIOPSIDE CaMgSi

Formula:

Complete

2

O

series to

Intermediate

ft .

CaFeSi 2 Oe = Hedenbergite

members =

Salite, Ferrosalite

Mn and Zn = Jeffersonite Diopside rich in Mn = Schefferite Diopside rich in Mn and Zn = Zinc Schefferite (variety) Ferrosalite rich in

a very rare gemstone indeed.

Name:

A

pegmatites.

ite

larger Turkish stones include: 157.66

(brown, emerald-cut— world's largest); 26.97

Comments:

None observed.

Luminescence:

Maine.

Hungary: good crystals. Postmasburg district. South Africa: manganiferous variety. Cornwall, England; Greenland; Norway; Sweden; France; Switzerland; Germany; Greece; USSR; Japan; China.

in the

Pleochroism:

Occurrence:

Chester County, Pennsylvania: fine transparent crystals

some

Strong.

crystals of very large size.

Chester, Massachusetts: with

up

0.013-0.014.

SW.

saehusetts); Turkish stones fluoresce green in

diaspeirein,

meaning

to scatter,

apart in the hot flame of a blowpipe.

in Cr = Chrome Diopside (variety) Diopside color varieties include baikalite, alalite and

Diopside rich

malacolite (pale green) and violane (purple).

DICKINSONITE Crystallography:

H

Formula:

2

Na6(Mn,Fe,Ca,Mg), 4 (P0 4 )i

Crystallography:

rhombohedral;

2

•

H

2

0.

Monoclinic. Crystals tabular, pseudo-

foliated,

micaceous, radiating.

Monoclinic. Crystals often well formed,

prismatic, stubby, also massive. Colorless, white, gray, pale green, dark green,

Colors:

blackish green, brown, yellowish to reddish brown, bright

green (Cr variety); rarely blue. Oil green, olive green, yellowish green, brown-

Colors:

brownish.

ish green,

Hardness: Density:

light to

dark brown.

Vitreous.

Luster:

3.5-4.

Hardness:

5.5-6.5.

3.38-3.41.

Usually 3.29; range 3.22-3.38 for diopside,

Density: Cleavage: Optics:

is

Hedenbergite always dark green, brownish green, or black.

Vitreous; pearly on cleavage.

Luster:

Schefferite

Perfect

a=

Biaxial (+),

and

easy,

1.648-1.658;

2V

-90°.

1

direction. Fracture uneven.

/J= 1.655-1.662;

y= 1.662-1.671.

higher

if

more Fe

Cleavage:

present.

Perfect

choidal. Brittle.

1

direction. Fracture

uneven to con-

DIOPTASE

Optics a

P y

Diopside

Hendenbergite

Jeffersonite

Scheffente

Chrome Diopside

1.664-1.695 1.672-1.701 1.695-1.721

1.716-1.726 723-1.730 1.741-1.751

1.713 1.722 1.745

1.676 1.683 1.705

1.668-1.674 1.680 1.698-1.702

1

52-62°

50-60°

21/

3.22-3.38 0.024-0.031

Density Birefringence Pleochroism

3.50-3.56 0.025-0.029 pale green/green-brown

none

Intermediate compositions have intermediate properties in the

diopside-hedenbergite series; increasing iron

content results in higher properties. salite

is:

The pleochroism of

pale green/blue-green/yellow-green.

Chrome diopside has lines at

Spectral:

83

plus fuzzy bands at 6350, 6550, 6700

5080, 5050, 4900,

and a doublet

74°

60°

55°

3.55

3.39 0.031

3.17-3.32

0.032 dark/light

brown

dark/light

0028

brown

yellow/green

Austrian diopsides are usually smaller but of fine color.

Diopside from Madagascar

is very dark green and less about 20 carats. Chrome diopsides are known up to about 10-15 carats. Most diopside localities provide material that cuts 2-10 carat gems.

up

attractive,

AMNH:

to

38.0 (green,

New

York).

at

SI: 133.0 (black, star, India); 24.1 (black, catseye, India);

6900.

Pale green diopside gives lines at 5050, 4930, and 4460.

Luminescence: Blue or cream white in S W, also orangeyellow; sometimes mauve in LW. May phosphoresce a peach color. Occurrence:

In Ca-rich

metamorphic rocks;

in kimberlite

19.2 (green, Madagascar); 6.8 (yellow, Italy); 4.6 (yellow,

Burma).

Comments: inlay

Violane has been used for beads and

— transparent material is always very tiny. The color

of this material

is

deep

being from Burma. Faceted diopside

(Cr-diopside).

Burma: yellow faceted gems;

also catseyes

and pale

Madagascar: very dark green cutting material. Sri Lanka: cuttable pebbles. Ontario, Canada: green faceting material. Quebec, Canada: red-brown material that cuts gems to 2

desirable. Hedenbergite

is

local

name). St.

Marcel, Piedmont, Italy: violet variety of diopside

very rare.

is

not extremely

tend always to

gem

Colors

most and the intermediate varieties be opaque except in very thin splinters.

are usually dark, so a bright

carats.

is

rare, but large (over 15 carats) clean stones are.

green faceting material.

Ala, Piedmont, Italy: fine green diopside (alalite

and

violet or blue

Catseye material cuts extremely sharp eyes, the best

and

attractive

is

Chrome diopside, quite rare in sizes over 3-4 carats, has become available in commercial quantities from the USSR. The color is excellent, with Cr content about 0.5% by weight.

Name:

Greek words meaning appearing double.

{violane). Zillerthal, Austria: fine

green crystals, some transparent.

Georgetown, California: green diopside. Crestmore,

DIOPTASE CuSi0 (OH) 2

Formula:

2

California: large crystals (non-gem).

DeKalb,

New

York: fine transparent green crystals up to

USSR: green

crystals {baikalite or malacolite);

and chrome diopside.

Outokumpu, Finland: fine deep green Cr-diopside. Nammakal, India: star stones and catseyes, also dark

Colors:

Rich emerald green, bluish green.

Streak:

Pale blue-green.

Luster:

Vitreous; greasy on fractures.

green facetable material. Franklin,

New

Jersey: jeffersonite, schefferite, and

Zn-schefferite.

Langban,

Sweden:

jeffersonite,

schefferite,

and Zn-

Hardness: Density:

Cleavage:

Kenya: chrome diopside.

uneven.

New York

of fine quality

common

material provides cutting rough

and large

size.

The

Italian, Swiss,

and

5.

3.28-3.35.

schefferite.

Stone Sizes:

Hexagonal. Fine crystals are

in certain localities; stubby, elongated.

several inches in length.

Slyudyanka,

Crystallography:

.

Perfect

1

direction. Fracture conchoidal to

Brittle.

o

Optics:

-

Uniaxial + ). (

1.644-1.658; e

=

1.697-1.709.

DOLOMITE

84

Birefringence:

Indices increase from dolomite values with increasing

0.053.

substitution of iron.

Dispersion:

0.036.

Broad band

Spectral:

and

of blue

at

about 5500; strong absorption

Luminescence:

Luminescence:

None.

weak brown

Oxidized zone of copper deposits.

Occurrence: Zaire; Chile;

white

USSR.

Arizona: microscopic crystals. Guchab and Tsumeb, Namibia: world's finest crystals,

some transparent but mostly filled with cleavage planes and fractures. These crystals are a superb color, on

may be

Crystals

fairly large,

but clean

areas within such crystals are always very small, and

stones are never larger than 1-2 carats.

Cabochons up

to

about 15 carats are sometimes cut from translucent masses.

Comments:

Dioptase is abundant in mineral collecworld and is not considered a great

tions throughout the

but faceted

rarity,

gems

are extremely rare due to a

paucity of clean fragments. Clean stones over

all.

Cabochons

1

carat are

and few collections have stones

virtually nonexistent,

at

are blue-green, translucent, and quite

attractive but are

much

to see

through

because the cleavage directions can be determined by looking into the crystals.

just

DOLOMITE

eral Region.

transparent.

Pribram, Czechoslovakia: cobaltian dolomite (pink).

Czechoslovakia and Hungary: kutnahorite. is a mineral of veins and hydrothermal or low-

Ankerite

temperature deposits. Stone Sizes: is

2

)2

a complete series from dolomite, through ferroan

dolomite, to ankerite.

(Mn

Colorless, white, gray, green, pale brown, pink

is

present). Ankerite

pink.

is

tan to brown, and kutnahorite

Dolomite may also be pink due

Luster:

to Co.

naturally color-

18.38 (Spain).

Dolomite

is

a rarely seen

gem with distinc-

is too soft and Spanish crystals are widely sold to collectors so transparent material is fairly abundant.

tive birefringence (as a

carbonate) but

fragile for wear.

After Deodat Dolomieu, French engineer and

mineralogist.

DOMEYKITE DRAVITE

See: Algodonite.

See: Tourmaline.

DUMORTIERITE

See

also: Holtite.

AbCMBOjMSiO^.

Formula: 3.5-4; varies with direction in crystal.

Crystallography:

Density:

generally carved; often

may be

stones over 100 carats.

Vitreous to pearly.

Hardness:

is

banded. Faceted dolomite from New Mexico reaches a size of about 5 carats. Spanish material can provide

Name:

Hexagonal (R). Crystals rhomb-shaped, sometimes with curved faces; saddle-shaped; massive or granular; twinning common. Crystallography:

Colors:

Massive material

stained pretty colors and

Comments:

CaMg(CO,) + Fe, Mn, Zu, Pb, Co. Note: CaFe(C0 3 )2 = Ankerite. CaMn(C0 3 = Kutnahorite. is

creamy

Keokuk, Iowa: in geodes. New Mexico: transparent material, cuttable. Eugua, Navarra, Spain: magnificent crystals and clusters, often large size, perfectly formed and completely

PC:

There

blue, pale green,

LW.

Switzerland.

too soft for wear.

From Greek words meaning

Formula:

Orange, blue, pale green, creamy white,

SW. Orange,

Occurrence: In sedimentary rocks; in Mg-rich igneous rocks that have been altered; geodes. Quebec, Cananda; Mexico; Brazil; Germany; Austria;

it

Name:

in

in

Missouri, Oklahoma, Kansas: so-called Tri-State Min-

matrix, and up to 2 inches long.

Stone Sizes:

Not diagnostic.

Spectral:

violet.

0.179-0.185. (Ankerite, 0.182-0.202).

Birefringence:

2.85, as high as 2.93; ankerite, 2.93-3.10.

Cleavage:

Perfect

1

direction. Fracture subconchoidal.

Orthorhombic. Crystals prismatic and

very rare; usually massive, fibrous, granular. Colors:

Blue, violet, brown, pinkish, blue-green, greenish.

Luster:

Vitreous to dull.

Brittle.

Optics:

dolomite: o

=

1.679-1.703; e

=

1.500-1.520.

Uniaxial (— ). ankerite: o

=

Uniaxial (— ).

Hardness: Density:

1.690-1.750; e

=

8-8.5; massive varieties 7.

3.26-3.41.

1.510-1.548.

Cleavage:

Good

1

direction, not observed in massive

material; fracture splintery or uneven.

DUMORTIERITE Optics: Brazil:

SG =

a = 1.686; /3 = 1.722; y = 1.723. a = 1.668-1.673;/? = 1.682-1.684; y = 1.685-1.688.

3.31-3.35.

Uniaxial

Birefringence:

Pleochroism:

0.15-0.37.

Black/brown/red-brown;

also: blue-black/

SW;

also blue-white

Luminescence:

Blue (France)

to violet (California) in

in

SW.

In

aluminous metamorphic rocks;

Pershing County, Nevada: violet

Stone Sizes: Massive blue and violet material occurs in pieces weighing several pounds. Only a small amount of facetable material has ever been discovered (Brazil, Sri Lanka), and these gems tend to be very small (under 1-2 carats). Only a few faceted dumortierites exist. Arizona dumortierite

is

actually a quartz-impregnated variety.

Dumortierite

is

a beautiful and very hard

The cabochon known form, since faceted

material, eminently suitable for jewelry.

pegmatites.

Arizona.

Lanka: transparent, reddish-brown stones.

Comments:

Not diagnostic.

Occurrence:

bluish-green material.

13-56°.

blue/colorless.

Spectral:

France; Madagascar; Brazil (Minas Gerais): facetable Sri

(~),2V=

85

gem

material in

is

the only generally

stones are so rare. Fibrous inclusions have been noted in the transparent Brazilian stones.

material.

Name:

After

M. Eugene Dumortier,

a paleontologist.

I

E1LAT STONE

doubtedly exist that have been sold as other Sri Lankan gems, but the total number of gems is a mere handful.

See Chrysocolla.

EKANITE Formula:

Name: (Th,U)(Ca,Fe,Pb) 2 Si 8

Tetragonal. Crystals elongated paral-

Crystallography: lel

Sri

2 o.

Green, dark brown,

Luster:

Vitreous.

Hardness: Density:

light

F.

ELBAITE

brown, emerald green.

L. D.

Ekanayake who

first

found

in a

it

gravel pit.

ELAEOLITE

to long crystal axis; massive pebbles.

Colors:

After

Lankan

See: Nepheline.

See: Tourmaline.

EMERALD

See: Beryl.

5-6.5.

ENSTATITE

3.28-3.32.

Orthopyroxene Group: Bronzite; Hyper-

sthene; Ferrohypersthene; Eulite; Orthoferrosilite.

None.

Cleavage:

=

=

1.573;

e

Uniaxial (-).

Gems

usually

Optics:

o

Composition: This is a complex solid-solution series involving Fe and Mg silicates. The series extends from enstatite: MgSiOi. through bronzite: (Mg,Fe)Si03, hypersthene(Fe,Mg)Si0 3 to orthoferrosilite: FeSiOi. Like the plagioclase feldspars, the series is arbitrarily broken into six regions of composition (numbers refer to percentage of orthoferrosilite molecule in formula):

1.572. =,

1.590-1.596.

,

Birefringence: Spectral:

0.001.

May show

Luminescence:

lines at

6300 and 6580.

Not diagnostic.

30

—I—

—t—

Occurrence:

Discovered in 1953 as waterworn, translucent green pebbles at Eheliyagoda, near Ratnapura, Sri Lanka. Occurs in the gem gravels. Some cut Sri

Bronzite

Enstatite

Ferrohypersthene

Hypersthene

Eulite

Orthorhombic. Crystals are prismatic most members of the series. Twin-

Crystallography:

and not

common

Quebec, Canada.

ning

common,

Central Asia.

crystals have interleaved lamellae of ortho-

Lankan stones have 4-rayed

stars.

Mt.

Ste.

Hilaire,

A

=

Colors:

351 carat rough has also been reported.

Comments:

Ekanite

is

metamict as a

result of the

U

visible as lamellae in crystals; often

and

clino-

Enstatite

is

colorless, gray, green, yellow,

and

brown. The same range applies to bronzite. Hypersthene is green, brown, and grayish black. Orthoferrosilite tends to be green or dark brown, generally somber tones.

1.595 (average); radioactive; 2 spectral lines seen.

Th content. The properties vary, depending on

for

pyroxenes.

Stone Sizes: A stone was tested by the London Gem Labs in 1975: 43.8 carats, blackish color, S.G. = 3.288, R.I.

is

100

—

Orthoferrosilite

and

Luster: Enstatite

the degree

breakdown of the structure. Ekanite is one of the very rarest of all gems, and only a few are known. More un-

metallic.

of

ferrosilite

86

is

vitreous. Bronzite

Hypersthene is

vitreous.

is

is

vitreous to sub-

vitreous, pearly, or silky. Ortho-

ENSTATITE 5-6 for the whole series.

Hardness:

and

See

Density:

table.

Good

Cleavage:

Hypersthene

in

1

direction for

(+)

)

(

)

all

species in series.

(

88

12

(+)

100

H

1—

I

Enstatile

Generally low and becomes zero

and

1

when

2^=50°. In general, lower than that for the clino-

Birefringence:

pyroxenes (see

table).

is an altered enstatite (S.G. = 2.6, hardness = opaque) from which cabochons are cut. Localities: Burma and Harz Mountains, Germany. Embilipitiya, Sri Lanka: colorless enstatite (cut gems up to =; 20 carats!) with R.I. = 1.658-1.668; birefringence =

Pleochroism:

The entire series has a characteristic

pleo-

=

1.665-1.675; birefringence

Spectral:

gems

All

in this series

5060 and often at 5475. Tanzanian gems: also diffuse

show

a strong line at

ROM:

brown, Austria).

PC:

4.5 (hypersthene,

lines at 4550, 4880,

and

LA: 80

None.

Mg-rich members of the series are comand ultrabasic rocks; also in layered intrusions; volcanic rocks: high-grade metamorphic rocks; regionally metamorphosed rocks and hornfels; meteorites. Gem enstatite occurs in Burma, Tanzania, and Arizona. Also noted from Mairimba Hill, Kenya (yellowish green;

Occurrence:

in basic

y=

1.662; birefringence

= 0.010; S.G. = 3.23).

Other noteworthy localities are Norway, California, and Germany. India produces 4-rayed star enstatites. Rare green gems come from Kimberley. South Africa. Bronzite comes from Mysore, India, and Styria, Austria: 6-rayed bronzite stars have been found.

Density Optics a P Y sign

Birefringence

(enstatite,

(dark brown cushion-cut, Africa).

been noted

1.652;

brown, Africa); 26.6

green, India).

Inclusions:

a=

7.8 (enstatite, brown, Sri Lanka); 3.9 (ensta-

,

tite,

5550.

mon

3.23.

12.97 (enstatite, Burma).

1.0, 8.1

1

Arizona gems: diffuse line at 4880. Sri Lankan gems: diffuse line at 5550. Brazilian and Indian gems: diffuse lines at 4880 and 5550. Other lines noted: 5090, 5025, 4830, 4590, and 4490.

Luminescence:

=

encountered, but Indian faceted gems over 10 carats

SI:

green/smoky green/green.

0.010; S.G.

stones. Indian star enstatites over 50 carats are frequent-

are rare.

y: pale

=

Stone Sizes: In general, gems from this series are small (large ones are too dark in color to be attractive), and crystals tend to be small. The exception is star stones, of which large examples exist. Enstatites and hypersthenes of 5-10 carats, if clean and lively in color, are very rare ly

pale greenish brown/pale reddish yellow/pale

3.25; quartz inclusions.

Ratnapura, Sri Lanka: green and brown enstatite with

a: pale red-brown/purplish/brown pink.

brown-yellow.

=

0.010; S.G.

chroism: pink to green.

/J:

material from Baja California,

3.5-4,

R.I.

Dispersion:

gem

Bastite

Orthoferrosilite

2V=90°

noted from Norway, Greenland, Germany,

is

California, with

Mexico.

Optic Sign: The optic sign changes along the series, from + to — and back to + ). The break points are at 12% and 88% orthoferrosilite: (

87

Tabular scales of hematite and goethite have hypersthene.

in

Comments:

Most gem

range 1.663-1.673.

enstatites have indices in the

The brown and green gems from

Tanzania are enstatites, as are the brownish-green stones from Sri Lanka. Green and brown gems from India and Brazil tend to be in the bronzite composition range. The

gems

of the orthopyroxene series are usually very dark,

slightly brittle

because of cleavage, and generally not

appealing for jewelry purposes.

The

4-rayed star

gems

are widely sold at a very low price, and the material

is

extremely plentiful. However, clean gems of hypersthene and enstatite are not abundant, except in very small (1-2

Even in this and muddy. These are carat) sizes.

Orthoferrosilite

gem

is

size the colors tend to all

be dark

true collector gemstones.

included for completeness and has no

significance.

Names:

Enstatite from the

because of

its

Greek

for

an opponent

high melting point. Bronzite

is

named

Enstatite

Bronzite

Hypersthene

Orthoferrosilite

3.20-3.30

3.30-3.43

3.43-3.90

3.90-3.96

1.650-1.665 1.653-1.671 1.658-1.680

1.665-1.686

1.686-1.755

1.755-1.768 1.763-1.770

1.680-1 703

1.703-1 .772

(+)

(-)

0.010

0.015

C-0C+) 0.017

(intermediate)

1

.772-1 788 C+]

0.018

for

EOSPHORITE

88

its

bronzy color and

Greek words

luster.

Hypersthene

from the

is

for very strong or tough. Orthoferrosilite

named for its crystallography and composition. named for its composition: Ba, Si, Ti.

Bastite

The

Formula:

X y3Z (0,OH,F),

is

Mn; Y

2

3

=-

if

X

where

Mn,

Al, Fe,

Ti;

=

Z=

is

Ca, Ce, La, Y, Th, Fe,

Si,

Be.

Ca AhSiiOi (OH). 2

2

Ca (Al,Fe)3Sb0 (OH).

£/?/tfote:

Series to Childrenite

3,

Zoisite and Clinozoisite:

also

EOSPHORITE

general formula of the epidote group

is

12

2

P/Wmo^/te:Ca2(Mn,Fe,AlhSi.,0,2(OH>

Fe exceeds Mn.

(also called piemontite).

(Mn,Fe)AlP0 4 (OH)

Formula:

Crystallography:

2

H

2

0.

^//art/7e.(Ca,Ce,La,Y) 2 (Mn,Fe,Al)3Si 1 0, 2 (OH).

MwM/m7
Monoclinic (pseudo-orthorhombic).

Crystals prismatic, often twinned. Colorless, pale pink, pale yellow, light brown,

Colors:

2

(Al 2 V)Si,0, 2 (OH).

//a«cocA:/Ve.(Pb,Ca,Sr) 2 (Al,Fe),Si,0, 2 (OH).

is

reddish brown, black.

All are monoclinic, except zoisite which orthorhombic. Crystals prismatic and tabular; also gran-

Crystallography:

ular,

massive, fibrous; sometimes twinned, often striated.

Vitreous to resinous.

Luster:

Colors:

Hardness: Density:

3.05 (pure

Mn

end member); 3.08

a=

1.638-1.639;

/J

=

1.660-1.664;

y=

(Brazil).

1.667-1.671.

Pleochroism:

Distinct: yellow/pink/pale pink to

Strong line at 4100, moderate

Occurrence: with

Mn

gray,

green,

at

4900

gray, grayish white,

Zoisite

is

light

brown

gray, green,

is

to black.

brown, pink

(thulite). yellowish,

blue to violet (tanzanite). Vitreous; pearly on cleavages; massive materi-

als dull. Allanite resinous, pitchy. (in

Hardness:

brownish-pink material).

Luminescence:

yellow,

Piedmontite is reddish brown, black, rose red, pink. Hancockite is brownish or black.

Luster:

colorless.

Spectral:

pale

Epidote shows shades of green, yellow,

Allanite 0.029-0.035. {Note: less than childrenite.)

Birefringence:

colorless,

greenish black, black.

2^=50°.

Biaxial (-),

is

pink; often zoned.

Poor; fracture uneven to subconchoidal.

Cleavage: Optics:

Clinozoisite

5.

montite

None observed.

6-7.

Luminescence: In granite pegmatites, usually associated

phosphates.

Maine; Keystone, South Dakota; North Groton, New Hampshire. Hagendorf, Germany. Minas Gerais, Brazil: excellent, flat, pink crystals up to 4 X 1 cm, at Itinga.

Epidote sometimes

slightly harder, pied-

softer.

Usually none. Thulite (pink zoisite) from

Nevada sometimes medium pale brown in SW. Also thulite from North Carolina is orangy-yellow in LW.

Branchville, Connecticut;

Stone Sizes: less

Cut eosphorites are always small, usually

than 3-4 carats. Cuttable crystals are usually very

small and badly flawed, only from the Brazil localities.

Cleavage:

Perfect

when The hardness makes

Pink gems are extremely attractive

Dispersion:

light

Zoisite:

the pink color.

EPIDOTE GROUP The epidote group consists of three related minerals that are fairly well known to collectors and hobbyists, plus one popular gem mineral and three less common species.

None

in

the

same

range.

in clinozoisite.

Distinct red to

brown/brownish yellow/greenish brown;

brown/brown/dark red-brown; colorless/pale

collections.

From Greek eosphoros. meaning dawn-bearing.

(different orienta-

yellowish brown in hancockite.

green/green.

in allusion to

all

For tanzanite: 0.019. Values for other epi-

Pleochroism:

cut, especially as round brilliants. wear unrecommended; cutting presents no great problems. This is a very rare gemstone, seen only in a few

Name:

direction in

dote group minerals are

Allanite: reddish

Comments:

1

tion in zoisite). Fracture conchoidal to uneven. Brittle.

Epidote: colorless, pale yellow or yellow-green/greenish yellow/yellow-green.

deep blue/purple/green

(tanzanite); reddish-

purple/blue/yellowish brown (tanzanite); pale pink/ colorless/ yellow; dark pink/pink/yellow (thulite).

Piedmontite: yellow/amethystine violet/red. Spectral: Most members of the group have nondiagnostic spectrum; epidote has a very strong line at 4550, weak line is sometimes seen at 4750. This spectrum is very

sensitive to direction within the material

and

ble in certain orientations. Tanzanite has a

is

not

visi-

broad absorp-

EPIDOTE GROUP tion in the yellow-green centered at 5950, with faint

and 4550 and a few weak

also at 5280

bands

Piemonte,

89

Italy: in sericite schists.

Egypt: in a porphyry, colored red by piedmontite. Hancockite:

lines in the red.

Occurrence: The minerals of the epidote group form low temperatures in low- to medium-grade metamorphic rocks. Allanite is more commonly found in igneous rocks such as pegmatites. Clinozoisite and epidote are also found in igneous rocks, and piedmontite is found in schists and manganese ore deposits. Zoisite occurs in calcareous rocks such as metamorphosed dolomites and

Franklin,

New Jersey: only notable locality, in small crystals.

at

Allanite:

Various localities throughout the United States. Canada; Norway; Sweden; Greenland; USSR; Madagascar. Zoisite:

South Dakota; Massachusetts.

Wyoming: greenish-gray

calcareous shales subjected to regional metamorphism. Epidote:

Washington:

McFall Mine, Ramona, California; Idaho; Colorado; Michigan; Connecticut; Massachusetts;

California

New Hampshire.

USSR; Japan; Korea; Australia; Kenya; Madagascar.

vakia;

many

localities.

Bourg d'Oisans, France; Italy:

Piedmont, other at

Tawmaw,

thulite.

fine crystals.

mium, with ruby

crystals.

localities.

Lelatema, Tanzania: fine blue-violet crystals, up to large

Untersulzhachthal, Austria: main source of faceting rough.

Burma:

thulite.

and Nevada:

North Carolina: thulite. Baja, Mexico; Scotland; Austria; Finland; USSR; Japan; Germany. Longido, Tanzania: deep green crystals, colored by chro-

Baja California, Mexico; Arendal, Norway; CzechosloSwitzerland:

material, sometimes tumble-

polished for jewelry.

a chrome-rich material, fine

size, often

deep

Norway:

green color (tawmawite).

gemmy

Greenland:

Lanka: yellow-brown (pleochroism = yellow-green/ brown/greenish-yellow); a = 1.718; /? = 1.734; y = 1.738;

(tanzanite).

thulite. thulite.

Sri

=

birefringence

0.020; S.G.

=

Stone Sizes:

3.33.

Outokumpu, Finland: chromiferous epidote (tawmawite). Minas Gerais, Brazil: cuttable, yellowish-green crystals birefringence 0.021; density 3.3-3.5).

Blue Ridge, Unaka Range, North Carolina (also

in Vir-

is

Georgia): unakite, a granite consisting of pink

feldspar and green epidote.

A

similar rock

is

also

is

in

huge blocks weighing

often cut into spheres as well as

cabochons. Facetable epidote is rare over 5 carat sizes, and cut clinozoisite tends to be even smaller. Allanite is hardly ever cut except as cabochons: piedmontite is opaque and massive, also cut only as cabochons. Tanzanite

(these are trichroic,low in iron; indices 1.722/1.737/1.743;

ginia.

Unakite occurs

many pounds and

the only

member

of the epidote group that reaches

large sizes in faceted gems.

known

Rough

tanzanite crystals

weighing hundreds of carats have been found.

from Zimbabwe.

SI: 122.7 (blue, tanzanite, Tanzania); 18.2 (blue catseye

Clinozoisite:

tanzanite, Tanzania); 3.9 (epidote, brown, Austria).

Nevada; Colorado. Timmons, Ontario. Canada; Ireland; Iceland; India;

DG: Italy;

7.30 (clinozoisite, brownish, Iran); 6.90 (epidote,

brown).

Switzerland; Austria; Czechoslovakia.

PC: 220

Kenya: gray-green crystals. Gavilanes, Baja, Mexico: brownish, facetable

light

(blue, tanzanite, Tanzania);

15 (clinozoisite,

brown-green, Baja).

crystals.

The epidote minerals

Piedmontite:

Comments:

Pennsylvania; Missouri.

and span a wide range of the gem market. Hancockite, from New Jersey is very rare, and if a faceted gem exists it would be extremely small (under

Scotland; Vermland, Sweden; Morbihan, France; Japan; Otago,

New

California

Density Optics a /3

y 21/

Zealand.

and Arizona: many

1-2 carats).

localities.

Clinozoisite

Epidote

Piedmontite

Hancockite

Allanite

Tanzanite

Zoisite

Thulite

3.21-3.38

3.38-3.49

3.45-3.52

4 03

3.4-4.2

3.35

3.15-3.38

3.09

1.788 1.810 1.830 (~)50°

1.640-1.791 1.650-1.815 1.660-1.828 ( + -340-123°

1.692 1.693 1.700

1.685-1.705

1.695

0.042

0.013-0.036

0.009

1.670-1.715 1.715-1.751 1.732-1.794 .675-1 .725 725-1 784 750-1 .807 1 1

are very interesting

1

.690-1 .734

(+)14-90°

.734-1 797 (-390-116°

1

1

1

.762-1 .829 ( + 32-9°

(

+

3

1688-1.710 1.697-1.725 (+30-60°

1.701

0.004-0.008

006

(-J

Bire-

fringence

0.005-0.015 0.015-0.049 0.025-0.073

ETTRINGITE

90

Epidote

gem

usually so dark in color that a large faceted

is

nearly black,

is

and uninteresting; small are often bright and lively,

lifeless,

stones, under 3-4 carats,

however. Clinozoisite

very rare

source

would be a better-looking gem, but

in sizes

over 5 carats.

The

only well-known

is

Piemonte (Piedmont). Unakite

is

named

after

Unaka range of mountains in the United States. Allanite is named after mineralogist T. Allan. Tawmawite is named after the Burmese locality. Mukhinite for A. S. Mukhin, Soviet geologist.

gem

Baja, Mexico, though an occasional crystal

is

gem. Allanite is very dark in color and seldom cut. The content of rare earth and radioactive elements causes it to become metamict with severe damage to the internal from another

in Italy,

the

ETTRINGITE

Series to Sturmanite.

locality yields a fine

Ca6 Al (S04)3(OH) .24H 0.

Formula:

2

12

Hexagonal; usually flattened hexago-

Crystallography: nal dipyramids;

2

sometimes prismatic,

fibrous.

crystalline structure.

Unakite rial

that

is

is

a widely used

and popular cabochon mate-

exported throughout the world.

known from

the United States, but Ireland,

It

is

best

Colors:

Colorless; transparent to translucent, milky.

Luster:

Vitreous.

Zimbabwe,

and probably other countries have similar rocks. Mukhinite is a very rare mineral, in small grains from Gornaya Shoriya, USSR, and has never been cut. Piedmontite is a distinct species but is often confused with thulite, which is a pink manganiferous variety of the species zoisite; piedmontite is dark brown or reddish in color, seldom in large masses, whereas thulite can occur in large pieces and is often bright pink in color. Both materials make lovely cabochons. Pure clinozoisite is very rare; it usually contains some iron, and there is a complete solid-solution series from it to epidote.

Hardness:

2-2.5.

Density:

1.77.

Perfect, rhombohedral.

Cleavage: Optics:

o

=

1.491;

Birefringence:

0.021.

None; colorless

Pleochroism:

Luminescence: Occurrence:

group and Tiffany

is

a variety

& Co. in connection with a trade promotion, and

has stuck although Tanzanite occurs locality,

known member of the epidote of zoisite. The name was given by

it

has no mineralogical significance.

in a variety of

colors at the Tanzanian

but most crystals are heated to about 700°F to

create a deep, intense blue with violet dichroism. Tanzanite soft and brittle, considering it is a popular ringstone, and great care should be exercised in wearing it. Inclusions that have been noted in tanzanite include actinolite, graphite, and staurolite. Epidote group materials often contain fibrous inclusions that create a chatoyancy and yield catseye gems when cut into cabochons. Catseye clinozoisite and epidote are known. Catseye tanzanites are very rare but have been found. is

ince,

None.

At type

Germany) in

Rhine Provmetamorphosed limestone igneous rocks. Also in metamorlocality (Ettringen,

cavities of

inclusions in alkaline

phosed limestones. Ettringen,

Germany:

In tiny crystals.

New Jersey: Minute

Franklin,

crystals.

South Africa: Associated with sturmanite at the Jwaneng mine, near Hotazel. The sturmanite forms yellowish coatings, with ettringite cores.

Stone Sizes:

Material from Ettringen and Franklin

microscopic.

A 2.5 carat pale yellow ettringite was faceted

is

from material found in the center of a mass of sturmanite from South Africa. This may be the largest known for the species.

Comments:

Ettringite

is

not generally facetable; any

cut stone would be considered an extreme

rarity.

South

African material has yielded minute stones, some of

Names:

Epidote is derived from Greek for increase because the base of the prism has one side longer than the other. Zoisite is named after Baron von Zois, who presented Werner, the great mineralogist, with the first specimens of the material. Thulite is after Thule, the ancient name for Norway. Tanzanite is the Tiffany & Co. tradename for blue zoisite, named after the country of origin, Tanzania. Clinozoisite

dehy-

Not diagnostic.

very rare. the best

in transmitted light;

drates and turns white. Spectral:

is

1.470.

Uniaxial (— ).

Tawmawite is a deep emerald-green epidote from Burma, the color of which is due to chromium. This material is Tanzanite

e=

is

the monoclinic

of zoisite. Piedmontite (piemontite)

is

dimorph

after the locality

which may have been labeled sturmanite.

Name:

After the locality in Germany.

EUCLASE Formula:

BeAlSi0 4 (OH).

Crystallography: well developed.

Crystals tabular or prismatic, often

,

EUDIALYTE

Colorless, white, pale blue, pale green, violet,

Colors:

dark blue, yellow.

Hardness:

6.5-7.5.

Cleavage:

May

Perfect

be variable within a single

=

3.08).

EUDIALYTE

direction; fracture conchoidal.

1

a = 1 .650-1.652; = 1.655-1.658; y = 1.671-1.676. + ), 2V = 50°. Dark blue (Zimbabwe): a = 1.652; /J = 1.656; y= 1.671; Optics:

(

=

0.019; S.G.

=

klasis (fracture),

crystal.

Na4(Ca,Fe,Ce,Mn) 2 ZrSi60,7(OH,Cl) 2 (Note:

Formula: Eucolite

birefringence

cleavage makes cutting a

From the Greek eu (easy) and because of the easy cleavage.

Brittle.

Biaxial

The

Name:

2.99-3. 10 (colorless

Density:

brilliant.

bit tricky.

Vitreous.

Luster:

gems can be very

91

.

—

calcium-rich variety.)

Hexagonal

Crystallography:

may be hexagonal or trigonal;

(trigonal); tabular crystals,

also prismatic,

rhombohe-

dral, massive.

3.06-3.13.

Shades of brownish red yellowish brown pink Often translucent.

Colors: Birefringence:

0.019-0.025.

Pleiochroism:

Zimbabwe dark

red.

blue material displays

,

,

Vitreous; greasy;

Luster:

may be

dull.

intense pleiochroic colors: azure blue/Prussian blue/

Hardness:

greenish-blue.

Dispersion:

if

Cr

is

in the

present,

it

4680 and 4550; may display a characteristic spectrum

Uniaxial

Euclase

is

blue, cobaltian hue,

some

District, Tanzania:

Colorado: Ireland: Austria:

about

Crystals are 1

more commonly found

in small

inch for colorless material. Most euclase,

colorless,

and strongly colored material

is

very

Blue and green gems are scarce over 2-3 carats,

also rare over 5-6 carats, although stones

20 carats have been cut.

museum

Gems

gems

up

to

are

about

reported over 50 carats

pieces. 12.5 green,

SI: 144 (lime green, Brazil); 48.7 (green):

Brazil; 8.9 (yellow, Brazil); 3.7 (blue-green, Brazil).

15.45 (colorless, Brazil); 14.0 (mint green, Brazil).

PC: 18.29 (blue-green

oval, Brazil); 7.43 (blue, Brazil);

Brazilian violet crystals reported that

up

would

yield stones

Not diagnostic.

Spectral:

Luminescence: Occurrence:

Not reported.

Nepheline syenites and associated peg-

matites:

Julienhaab District, Greenland: crystals up to

1

inch

in

Kola Peninsula, USSR: Pilansberg, South Africa. Madagascar. Magnet Cove, Arkansas: rich red color, in feldspar.

Euclase

safely in jewelry.

Mt. e

Ste. Hilaire,

=

It

is

may

a hard

enough gem

to

be worn

Quebec, Canada: facetable

1.600; birefringence

=

(o

=

1.596;

0.004).

Kipawa Complex, Sheffield Lake, Temiscamingue County. Quebec, Canada: red, facetable. Sweden: o = 1.598; e = 1.604; birefringence = 0.004: S.G.

=

2.88.

Stone Sizes: Faceted gems well under 1 carat in size have been cut from Quebec material. These are deep red and extremely rare. NMC: 0.30, 0.40 (intense red, Sheffield Lake, Quebec,

Canada).

Comments:

to 10 carats.

Comments: (if

Varies with body color.

Pleochroism:

A mpasibitika,

with violet being the most unusual. Colorless

DG:

0.003-0.010.

length.

Stone Sizes:

are

1.594-1.633.

sign variable (eucolite reported to be

like fine sapphire.

Norway.

rare.

)

a mineral of granite pegmatites.

Orenburg District, South Urals, USSR: cuttable crystals. Miami, Zimbabwe: cuttable crystals in shades of intense

is

+ but

=

)

Vista (cuttable crystals).

in fact,

(

1.591-1.623; e

(— with higher indices and S.G.).

Feeble or none.

Minas Gerais, Brazil: Ouro Preto (fine gem material in good crystals up to a length of about 6 cm); Santana de Encoberto (material with high birefringence and included crystals of apatite, hematite, rutile, and zircon); Boa

sizes,

=

o

Optics:

Birefringence:

Occurrence:

Morogoro

Basal, indistinct; fracture uneven; brittle.

Cleavage:

at

red with a doublet at 7050.

Luminescence:

2.74-2.98.

Density:

0.016.

There are two vague bands

Spectral:

5-5.5.

Although cabochons could be cut from

massive eudialite or translucent crystals, transparent material

suitable for faceting

is

elusive

and always small.

not be terribly exciting to look at

colorless), but the colored

gems

are truly beautiful

and exceedingly rare over a few carats

in size.

These

Name:

From Greek words meaning easy

because of

its

easy solubility in acids.

to dissolve

92

EUXENITE

EULITE

Luminescence:

See: Enstatite.

Occurrence:

EUXENITE

6;

Polycrase: (Y,Ca,Ce,U,Th)(Ti,Nb,Tah0 6

Crystallography:

.

Orthorhombic. Crystals prismatic,

stubby; as aggregates; massive.

green.

Streak:

Grayish, yellow-brown.

Luster:

Submetallic; vitreous to resinous.

Hardness:

on the Ta content and

Optics:

None. Fracture conchoidal.

Isotropic

due

Gems cut from euxenite are almost always

to metamictization. TV = 2.06-2.24.

is

seldom transparent.

are cut by collectors, but these are not very striking.

colors of faceted stones would be too dark to

make

them appealing.

of the Brittle.

Brazil; Finland; Zaire;

Comments: Euxenite is seldom seen in collections. Most collectors would not regard the mineral as facetable, but transparent fragments and areas of crystals have been noted that could cut small gems. Sometimes cabochons

Name:

hydration.

Cleavage:

Stone Sizes:

The

5.5-6.5.

4.30-5.87 depending

Density:

Norway; Canada; Greenland; Madagascar; Australia. Wyoming: large crystals.

small, as the material

Black, sometimes with a tinge of brown or

Colors:

In granite pegmatites; also as detrital grains.

California; Colorado; Pennsylvania; Maine.

Series to Polycrase.

(Y,Ca,Ce,U,Th)(Nb,Ta,Ti) 2

Formula:

None.

From the Greek euxenos (hospitable) because many useful elements it contains. Polycrase is

from the Greek, meaning mixture of many, also sion to the composition.

in allu-

FAYALITE

See: Olivine.

of intergrowth, composition of the minerals involved,

and the

FELDSPARS

depend on the and the cooling which may be very complex. It is

size of the included crystals all

original high-temperature composition

Feldspars are the most surface. In fact,

if

common

minerals at the Earth's

crust were regarded as a single mineral, late

it

why it may take years for a mineralogist simply to understand the complexities of the feldspar group, let alone contribute new data. easy to see

would calcu-

out almost exactly as a feldspar.

The

feldspars are

complex aluminosilicate minerals

containing K, Na, and Ca, with Ba.

history of the feldspar,

the entire composition of the Earth's

The

some

These complications, while both troublesome and

rarer types rich in

intriguing to mineralogists, are not critical to gemological

structures of these species are very similar.

feldspar cools,

it

may

a

insofar as these are relevant to gemstones. Potassium Feldspars: These all have the composition KAlSijOs but differ in structure. Orthoclase is monoclinic; Sanidine and Anorthoclase are also monoclinic, but the distributions of atoms within the structures are distinctive and different from each other and orthoclase. Microcline is triclinic. The properties are summarized in ties,

segregate internally into separate

mineral crystals, one type oriented within the other accord-

symmetry of the host crystal. The

ing to the

We may therefore simplify the discussion to summary of the basic feldspar species and their proper-

discussions.

However, most feldspars crystallize from a melt in igneous rocks. The structures at high temperatures are different from those at low temperatures. In addition, the various compositions that may exist at high temperatures may not be stable at low temperatures. When a

specific type

Properties of the Potassium Feldspars

Orthoclase

Microcline

Crystallography

Twinning

Hardness Density Optics a

P y

Triclinic

Lamellar twinning 6-6.5 2.54-2.63 1 1

not seen

514-1 .529 .518-1 .533

1.521-1.539

sign 21/

is

Monoclinic in the potassium feldspars 6-6.5 2.55-2.63 1

1.522-1.533 1.522-1.534

(-)

—

Luminescence

yellow-green

18-54°

—

0.012 strong in

LW; inert SW; green in X-rays.

4200

line;

bands at 4450, 4200 weak blue in LW or orange in SW; white to violet in X-rays.

93

.518-1 .527

C-3

33-103°

distinct

6

2.56-2.62

1.522-1.533 1.522-1.539

C-]

none

Monoclinic

1.518-1 529

66-103°

Dispersion Spectral

Sanidine/ Anorthoclase

none

distinct

not reported

FELDSPARS

94

the table below. Sanidine and Anorthoclase contain appre-

1

590

1

580

ciable sodium.

Plagioclase Feldspars:

The term

plagioclase indicates

a solid-solution series, ranging in composition from albite

1-570

(NaAlSiiOs) to anorthite (CaAl2Si 2 O s ); for convenience the series

was long ago

arbitrarily divided into six dis-

tinct species as follows: albite (Ab);

andesine (Ad); labradorite (La); bytownite (By); anorthite

The

(An).

series

1

560

1

550

1

540

oligoclase (Og);

7->

divided according to the relative

is

percentages of albite

anorthite:

vs.

a 1-530

Ah Ah

An

Ok \—

I

H 70

90

100

50

1

30

1

520 20

10

40

30

60

50

An, weight

The optical parameters vary

nearly linearly with

diffraction

work

Most plagioclase crystals are twinned

according to various laws related to the crystal struc-

and also the distribution of atoms in the structures. Zoning is common and is due to variation in the growth history of the crystals and to the fact that, in a magma, the composition of the melt changes as crystallization proceeds and minerals are extracted from the molten tures

The

properties of a plagioclase crystal

may

there-

fore vary widely within a small grain. Plagioclases also

are often clouded, that

is,

contain dustlike particles of

other minerals, including spinel,

rutile, garnet,

magne-

clinozoisite, muscovite.

Compositions within the feldspar group are complicated by the fact that structure or

Na

K may

enter the plagioclase

the orthoclase structure.

compositions are

know

The

refraction. Schiller

100

as ternary (three-component)

but at low temperatures unmixing occurs, that

and yellow. The color may be uniform or vary within a

Most feldspar (in

and all the feldspars two directions. The luster is vitreous, inclining to pearly on the cleavages. Feldspars are sometimes massive, cleavable, or granular. Microcline may be colorless, white, pink, yellow, red, All the plagioclases are triclinic,

have excellent cleavage

gray, or

green to blue-green.

gem circles, and is

gray,

Occurrence:

another feldspar gives

popular as

in

amazo-

plagioclases are is

is

all

colorless, pinkish,

colorless, white, or

often broken by spectacular

Moonstones may be colored by impuri-

such as goethite (brown).

Microcline

in

The

although the drabness

with oligoclase or orthoclase), sunstone, moonstone, and

which are albite-oligoclase mixtures. The

is

known

usually colorless, white, gray, yellow, red-

is

Schiller effects. ties

latter color

and greenish, whereas sanidine

This creates such oddities as perthites (mixtures of albite

presence of feldspar lamellae

The

the blue-green variety

widely cut into cabochons, beads, and carvings.

Orthoclase

a

separate feldspar phases, one distributed within the other.

peristerites,

in

sta-

segregation of the potassic and sodic molecules into

and flattened and

crystals are tabular

the case of plagioclase) usually complexly twinned.

or brownish. is,

light

best developed in labradorites,

single feldspar crystal.

feldspars. In addition, as in the plagioclase series itself,

high-temperature mixed feldspar compositions are

is

creating a lovely color play in shades of green, blue, gold

nite

resulting

an iridescence due to

rise to the Schiller effect,

dish,

ble,

90

compo-

usually advised in identification of a

is

plagioclase feldspar.

tite,

80

but because of the structural complexities, X-ray

sition,

mass.

70

%

Microcline occurs

in acidic alkali-rich plu-

tonic rocks; also in rocks such as pegmatites, granites, syenites,

and

schists.

Properties of Plagioclase Feldspars Albite

Hardness

of

all

Density Optics a

species = 6-6.5 2.57-2.69

Oligoclase

Andesine

Labradorite

Bytownite

Anorthite

2.62-2.67

2.65-2.69

2.69-2.72

2.72-2.75

2.75-2.77

1.543 1.548

1.560 1.563 1.572

1.561

1.577 1.585 1.590

1.538

1.542 1.546 1.549

sign

C+3

(-)

(+/-)

C+3

C-3

C-)

21/

77° 011

82° 0.007

76-86°

85°

0.008

0.012

86° 0.009

70° 0.013

P y

Birefringence

1.527

1531

1.551

1.565 1.570

FELDSPARS Pala, California;

New

Maine;

York; North Carolina.

USSR; Norway; Sweden; Germany;

clase

Japan; South

Italy;

moonstone

is

also found

and

will

95

be discussed with

plagioclase moonstones.

Africa.

Colorado (Pike's Peak area): amazonite. Amelia Courthouse. Virginia: finest amazonite in the United States. South Dakota: perthite. Canada: perthite, especially Ontario and Quebec.

Sanidine

Occurrence: A component of acid igneous rocks. Oregon; California. Near Koblenz, Germany: brown transparent gems; S.G. 1.520-1.525/1.522-1.526.

Brazil: fine amazonite.

Ashton. Idaho: sanidine crystals

India (Kashmir District): amazonite.

in

volcanic

tuff,

up

to

1

cm, colorless, well formed. Indices: 1.516-1.519/

Australia (Harts Range).

2V

1.520-1.522/1.521-1.523;

Amazonite cabochons up

Stone Sizes:

1.516-1.520/

2.57-2.58; birefringence 0.007; indices:

size are available; the material

is

almost any

to

usually sold by the

pound to hobbyists. The same applies to perthite. The Amelia material has fine color and translucency, but

=-

8-19°;

birefringence

0.003-0.005.

Stone Sizes:

Sanidine

is

not a

common

mineral and

is

hardly ever seen as a gemstone. Crystals tend to be colorless

and nondescript and are

rare in cuttable sizes.

perfect cleavage adds fragility.

Comments: Microcline crystals, associated with smoky

Comments:

with

little

Sanidine

gem

is

a mineral of volcanic rocks,

significance.

quartz, are popular mineral specimens from the Pike's

Peak area of Colorado. The color of amazonite ranges from pale green to dark green and blue-green. Pinkish orthoclase

is

Perthite

Occurrence:

Perthite

also often present as an intergrowth.

texture

Occurrence: A component of many rocks, especially alkalic and plutonic acid rocks, also granites, pegma-

history,

localities in the

United

from the

St.

known

as adularia (S.G.

=

Gotthard Region; the material con-

some Na.

Itrongahy,

Madagascar:

fine, transparent yellow ortho-

clase in large crystals, usually with

rounded

faces. (Indi-

ces 1.522/1.527; birefringence 0.005; S.G. 2.56.) Faceted

gems may be very

large

and deep

inches.

Tvedestrand, Norway: orthoclase sunstone, deep red-

orange, in masses up to a few inches in

Lanka:

in the

gem

other countries.

size.

Peristerite

Occurrence: Peristerite is well known from Ontario, Canada, where it is very abundant. It is also found at Kioo Hill, Kenya: S.G. 2.63; a = 1.531; /J = 1.535; y = 1.539.

gravels.

gravels.

Comments:

Compositions in the calcic oligoclase range to an inhomogeneous mixture of two feldspars, producing a Schiller, which in the case of peristerites is white or bluish. The effect seems to emanate within the body of the feldspar as a kind of glow. (Ab76> cool

Stones Sizes:

Madagascar produces by

far the largest

cuttable orthoclase known. SI: 249.6 (yellow,

Madagascar); 104.5 (pale green catseye,

Lanka); 22.7 (white

star, Sri

and unmix

Lanka); 6.0 (colorless,

North Carolina).

Albite

Composition:

Comments:

Sri

Lanka.

Some

of these (Sri Lankan)

stones are also asteriated. Yellow faceted orthoclase

handsome gemstone. Unfortunately, less

Ab,oo-Ab».

Yellow and colorless catseye gems are known

from Burma and

it

compo-

and therefore must be considered one of the most abundant mineral associations in nature. Fine perthite that is suitable for cutting comes from Dungannon Township. Ontario, Canada, in large pieces, and from various localities in Quebec, as well as from sitions

in color.

Greenland: brownish transparent crystals to more than 2

Sri

Schiller. Perthitic intergrowths

are very typical of the whole range of plagioclase

Switzerland: fine crystals,

Burma:

ent feldspars in the mixture. Usually perthite consists of

golden yellow or white

States.

Canada.

Sri

albite, oligo-

characteristic

brown and white lamellae; the white feldspar often has a

tites, syenites.

tains

The

produced by unmixing from high temperature. of the material depends on the cooling and hence the relative crystal sizes of the differ-

The appearance

2.56),

an intergrowth of

is

Orthoclase

Many

is

clase, plus orthoclase or microcline.

the cleavage

advantageous for wear. Also, fine rough

find, but large stones are displayed in

is

is

a

makes

Crystallography:

Colors:

Triclinia Twinned; platy crystals.

Colorless, white, yellow, pink, gray, reddish,

greenish.

hard to

museums. Ortho-

Luster:

Vitreous to pearly.

FELDSPARS

96

Luminescence:

may be

Usually none;

whitish

in

LW,

lime green in X-rays (Kenya).

Not diagnostic.

Spectral:

Occurrence: it is

Albite usually forms at low temperatures;

common

in

large sizes (over 15 carats).

pegmatites, granite, and other igneous

metamorphic rocks,

rocks, various

and displays a white to blue sheen. The body colors may be white, blue, or reddish brown. The blue-sheen material, especially when the body of the moonstone is colorless and transparent,. is very rare and greatly prized in

also marbles.

Essex County, New York. Ontario, Canada; Quebec, Canada; Madagascar; Austria. Rutherford Mine, Amelia, Virginia: fine colorless albite,

known

facetable, large; crystals are platy variety

Grant County, ity

as

c leave landite.

New Mexico produces a very fine qual-

sanidine moonstone with a blue sheen. Orthoclase

moonstone from Virginia is of a qualjty comparable to the Sri Lankan material: indices 1.518-1.524; birefringence 0.006. Moonstone also comes from Tanzania and several localities in the United States.

Moonstones are characterized by fissure in the body of the material created by exsolution pressures. Such fissure Inclusions:

Upson County, Georgia: moonstone.

systems along incipient cleavages

South Dakota: cleavelandite. Brazil: cleavelandite.

systems are short parallel cracks with shorter cracks

Kenya: colorless crystals, some with blue or yellow

tinge.

ROM:

about 50 carats are known. 12.25 (catseye, Burma).

emanating perpendicularly along the length of the parallel fissures. These resemble many-legged insects under the microscope and are known as centipedes. Moonstones also have rectangular dark areas due to stress cracking or negative crystals. Sometimes a cavity extends from such a rectangular dark area that creates an inclusion with a comma shape. Burmese moonstones are

DG:

characterized by oriented needle inclusions.

(Indices: 1.535/1.539/1.544; S.G. 2.63).

Many

other localities worldwide.

Stone Sizes: Clean gems are usually in the 1-3 carat range, from cleavelandite crystals. Catseye gems up to

11.13 (cateye, white).

Comments: is

Translucent albite

is

sometimes found that

colored a rich green by inclusions of chrome-rich

jadeite. Albite

sometimes intergrown with emerald,

is

especially in the strange hexagonal skeletal crystals

as trapiche emeralds. Facetable aibite

has indices: a

=

1.530-1.531;

f>

=

known

from Madagascar

y =

1.532-1.533;

1.539-1.540; birefringence 0.009-0.010; density 2.62. Small

faceted

gems

are fairly rare, almost always from the tips

of cleavelandite crystals. Albite

gems

are colorless in

most cases and not exciting to look at. Albite moonstones are known from many localities (discussed below).

Moonstone Moonstone tion

refers to feldspar of widely varying

and from a wide variety of

attribute

is

composi-

The

localities.

basic

one on cooling.

the presence of finely dispersed plates of

feldspar within another as a result of unmixing

Orthoclase moonstone consists of albite within an A blue color is produced if the albite

orthoclase matrix.

crystals are very fine; the

plates are thick.

The

sheen

is

white

if

the albite

color of the orthoclase

may be

Stone Sizes:

Moonstone

stones over 15-20 carats. Stones with a silvery or white

adularescence are abundant and available

hundreds of

stone

In

many

cases faceted

have the instrumentation needed to pin

down

the spe-

This is accomplished by a combination of optical and X-ray analysis. A few plagioclase gems have been

cies.

well characterized, however, and reported in the literature.

Occurrence:

tals.

clase

The is

is

reported from the

Hawk

in colorless to pale

Mine, Bakersville,

green facetable crys-

indices are 1.537-1.547; density 2.651. Oligo-

also reported from Kenya, colorless grains, with

a = 1.538-1.540, /3 = 1.542-1.544, y =

density of such material

1.549-1.550; birefringence 0.010-0.011; S.G. 2.64. North

is

2.56-2.59; material

Sri

is

are identified as a feld-

indices as follows:

Lanka tends to be at the low end of this range, material from India at the higher end. The refractive index

gems

spar in the plagioclase series, but the finder does not

referred to as adularescence.

is

The from

to

cases transparent crystals are rare.

Oligoclase

Some of this material cuts fine catseyes, where the sheen is concentrated into a narrow band. The sheen in moon-

up

Oligoclase, Andesine, Bytownite, Anorthite These feldspars are rarely encountered in gem form. Their occurrence is widespread throughout the world, in a great variety of rock types and environments, but in most

North Carolina,

to goethite (iron oxide) inclusions.

in sizes

carats.

Red coloration

due

and body color is

rare in both large size

abundant and very inexpensive. This is fortunate because the material is well cut and very attractive. Moonstone with a blue sheen is the most valuable and is rare in

white, beige, brown, red-brown, greenish, or yellowish. is

is

fine quality, but Indian material with strong

usually 1.520-1.525; birefringence 0.005.

The moonstone from Burma and Sri Lanka

is

adularia

Carolina gems up to about 1-5 carats, colorless to pale W. T.,

green, are reported. Oligoclase from Baffin Island,

N

Canada has yielded cut gems up to about 5 carats. Andesine is known from many localities, including

FELDSPARS California; Utah; Colorado; South Dakota; Minnesota;

New

York; North Carolina; Colombia; Argentina; Green-

land; India;

Norway; France; and Japan.

Bytownite

is

found

Germany; South Africa;

Italy;

plutonic rocks,

some meta-

morphic rocks, and meteorites. Localities include Montana; South Dakota; Oklahoma; Minnesota; Wisconsin; Scotland; England; Sweden; Japan; and South Africa. Bytownite is sometimes reddish in color and pebbles from Arizona and New Mexico have been faceted into small gems. Bytownite is also reported from Plush. Oregon, but this is a well-known locality for labradorite in facetable crystals;

it

may be

that

townite range.

Anorthite is the most calcic of the plagioclases, and sometimes makes up a distinctive rock known as anorthosite, which has been extensively studied. Localities for the mineral include Pala. California; Grass Valley, Nevada; Italian Mountains, Colorado; Greenland; England; Sweden; Finland; Italy; Sicily; India; and Japan. Anorthite has been cut for collectors but very rarely, and faceted

gems are always small. However, a locality on Great Sitkin Island, Alaska has yielded cut gems as large as 8 carats. This pale yellow anorthite may be the largest known. Labradorite the feldspars, none besides orthoclase

all

colorless/light yellow bluish green/light red-

Yellow

violet/ reddish

blue-green [multicolored]

orange

bluish green/light orange/

Bluish green

colorless orange/light reddish purple

Red orange Orange

orange/reddish orange bluish green/light orange red-violet/ reddish orange/ bluish green

Yellowish green

Blue-green and violet

some of the feldspar has

a borderline composition and crosses over into the by-

Of

Pleochroism

Stone Color

Red-orange and

in basic

97

quently encountered as a faceted

gem

as

is

is

as fre-

labradorite.

Other Effects: A labradorite moonstone is known from Madagascar. It has a blue sheen and the indices are: a = 1.550-1.553;

y=

1.560-1.561

;

birefringence 0.008-0.010;

S.G. 2.70.

Occurrence: Labradorite is best known from Nain, Labrador: crystals here are up to 2 feet long, but are badly cracked.

New York; Texas. Modoc County, California:

facetable crystals to

1

inch.

Finland: fine Schiller, very intense; cut stones called spectrolite.

Clear Lake, Millard County, Utah: facetable crystals.

Nevada: facetable crystals. Madagascar: moonstone effect. Australia: pale yellow, transparent material; indices

a =

The material ranges in color from colorless to yellow, but

1.556,y=

inclusions of minerals such as hematite and copper cre-

Oregon: facetable; labradorite has the following properties:

wide range of other body colors. These are best known from localities in Oregon. In addition, the phenomenon of Schiller is best developed in the labradorite range of plagioclase compositions. Translucent to opaque labradorite that shows blue, green, and golden Schiller

a = 1.559-1.563; y = 1.569-1.573; birefringence 0.008;

ate a

widely cut by hobbyists. Labradorite with Schilalso a component of many dark-colored igneous

colors ler is

is

rocks that are used materials.

in

building and construction as facing

Such rocks are very

attractive

when

polished

because the blue sheen of the labradorite grains flashes out at

many

different angles.

Zircon and magnetite; also ilmenite and (Madagascar). Hematite inclusions create an aventurescence or sparkly effect due to reflection off Inclusions:

rutile tablets

of parallel included flakes. This reflection creates a ing sheen of golden red spangles, leading to the

sunstone. Sunstone

is

roll-

name

also characteristic of oligoclase

and is discussed below. Microscopic particles of metallic copper and lead account for some of the unusual colors observed in Oregon labradorite. Pleochroism:

Usually absent

ble in labradorite

in feldspars

from Oregon.

darker-colored stones:

It is

but most nota-

better developed in

1-564; S.G. 2.695.

S.G. 2.71-2.73; material

Stone Sizes:

is

Ab^A^s.

Labradorite rocks are available

in

very

large sizes, suitable for facings of office buildings. This

material

is

also

sometimes cut into cabochons. Labra-

dorite in larger crystals, with uniform Schiller (rather than in smaller, randomly oriented grains) is frequently cut into cabochons by hobbyists. The best material for this purpose comes from Finland, but the material is not common and is fairly expensive compared to other feldspars. Faceted gems up to about 130 carats are known. It is likely that somewhat larger material exists, but fractur-

ing of rough prevents the cutting of larger stones. SI: 11.1 (yellow, Utah); 5.8 (yellow, Nevada); 30 (pale

yellow, Idaho); 23.8 (yellow, Oregon); 39 (yellow, Ore-

gon); 23.43 (yellow, Mexico).

PC: 62.5 (yellow, Mexico). LA: 129 (yellow, Mexico).

Comments:

The

Schiller in labradorite

is

similar to

that in peristerite, but the color range includes blue,

green, blue-green, gold, yellow, and purple. play

is

The

color

iridescent like the feathers of a peacock.

Faceted labradorite makes a handsome, although unu-

FERGUSONITE

98

sual jewelry stone.

It is

as hard as

the other feldspars that are the cleavage

is

worn

moonstone or any of

regularly in jewelry, but

always worth minding.

Gems

larger than

20 carats can be considered exceptional. Oregon material is abundantly available in the 2-10 carat range. Oregon gems are colorless to pale yellow but often are green or red-orange with a pink Schiller. These odd colors are

due

to

copper and lead, and the Schiller

is

due

to colloi-

Oligoclase

comes from Greek words meaning

break because the cleavage was believed to be

little

less per-

than in albite. Andesine is named after the Andes Mountains of South America. Bytown, Canada, gave its name to bytownite. Anorthite is from the Greek words an plus orthos, meaning not straight, because the crystal faces meet at an oblique angle. Labradorite was, of course, named for its occurrence in Labrador. fect

dal copper.

Sunstone This material contains hematite or goethite inclusions, which reflect light in parallel orientation and create a sparkling sheen in gold to brown color shades. Sunstone may be oligoclase or labradorite in composition and is much admired as a cabochon material among hobbyists. Very fine material is not abundant and is hard to obtain. Occurrence: New Mexico;

New

FERGUSONITE

Series to Formanite:

YNbO^ +

Formula:

Crystallography: idal; usually

Er,

Ce, Fe,

YTa0

4.

Ti.

Tetragonal Crystals prismatic, pyram-

masses.

Black, brownish black; surface altered brown,

Colors:

gray, or yellow.

brown, brown.

Streak:

Greenish

Luster:

Vitreous; submetallic; alters to dull surface.

gray, yellowish

York; North Carolina; Maine; Penn-

sylvania; Virginia.

Lake Baikal, USSR; Bancroft area, Ontario, Canada. Tvedestrand and Hittero, Norway; as masses in quartz

Hardness: Density:

5.5-6.5. 5.6-5.8.

Formanite: 7.03 (calculated).

veins.

Lake Huron (Canada Kangayam, India.

side):

brownish to pink color.

Harts Range, NT., Australia: an untwinned microcline microperthite with aventurine-type reflections due to inclusions of thin, brownish-red hexagonal inclusions, in

two

sets at

1.525;

y =

=

hardness

90° angles. Properties are: a 1.527; birefringence 6-6.5;

UV

1.520;

0.007; S.G.

=

/J

may

2.57;

fluorescence.

reach 100 carats or more. Most available is because and cracked.

material cuts smaller stones, however. This the rough

is

usually badly shattered

Names: Microcline is from Greek words meaning small and inclined because the cleavage is close to but not quite 90°. Amazonite is named after the Amazon River basin in South America. Orthoclase is from Greek words meaning break straight because the cleavages are at 90°. Sanidine is also from the Greek, sanis, meaning board,

in

reference to the tabular crystals. Anorthoclase

is

from Greek words for not upright because the cleavage

is

not 90°.

Feldspar is from the Swedish feldt + spat because it was found in fields overlying granite. Plagioclase is from the Greek, meaning oblique cleavage. Albite comes from the Latin albus, meaning white,

because the mineral

is

usually white, Perthite

for the locality, Perth, Ontario,

is

named

Canada. Adularia

is

Optics:

Isotropic

due

to metamictization.

N = 2.05-2.19

(mean), variable.

Pleochroism:

Weak.

=

Cabochons from Norwegian and Indian

Stone Sizes: material

no

=

=

Traces. Fracture subconchoidal. Brittle.

Cleavage:

Occurrence: Granite pegmatites rich in rare earths. California; North Carolina; Virginia; Texas; Massachusetts. Norway; USSR; Ytterby, Sweden; East Africa; Zimbabwe; Madagascar. Formanite is from Western Australia. Stone Sizes:

Cabochons

are cut to several inches

massive material. Faceted stones are extremely tiny than

1

name from Adular-Bergstock, Switzerwhere the variety occurs. Peris terite is from the Greek word peristera, meaning pigeon. The name moon-

is not abundant and is known Cabochons are cut merely as curiosities, as they have no special features that would recommend them except rarity. There are reports of

Comments:

This mineral

from various

localities.

transparent grains or parts of crystals that have been cut by collectors, but these are merely curiosities and are seldom encountered.

Name:

After Robert Ferguson, a Scottish physician.

FERROHYPERSTHENE FERROSALITE

See: Enstatite.

See: Diopside.

FERROSILITE

See: Enstatite.

land,

stone alludes to the lustrous sheen of this material,

same way

that sunstone derives

its

name.

(less

carat).

also

a locality-derived

from

FERROTANTALITE

See: Manganotantalite.

in the

FIBROLITE

See: Sillimanite.

FRIEDELITE

AGATE

FIRE

Occurs

Rosiclare.

See: Quartz.

in

many colors in

Illinois, also

99

Missouri

(purple, blue, yellow, brown, colorless).

FLINT

New Hampshire: bright green fluorite up to 8 inches across. Ontario, Canada: banded, violet material in calcite. Colombia: (green). Huanzala, Peru: pink crystals. Westmoreland,

See: Quartz.

in

crystals

FLOWSTONE

See: Calcite.

FLUORITE Formula:

Crystallography:

Isometric. Usually in

good

ties.

crystals,

massive, granular.

less,

purple (various shades), green (various shades),

blue-green, blue, yellow to orange,

brown

(various shades),

white, pink, red, brownish red, pinkish red, brownish black, black. Crystals are frequently color-zoned.

729 (green, Colombia); 492, 354 (pink, Korea); 348

(green,

New

let, Illinois);

Hampshire);

Illinois); 13 (pink,

DG:

1

17 (green, Africa); 11 1.2 (vio-

118.5, 85.4 (blue, Illinois); 32.7 (colorless,

Switzerland).

68 (deep blue, Namibia), 23.7 (pink, Africa); 72.4

(green).

LA:

180 (green.

New

Hampshire).

1031 (yellow, triangle, Cave-in-Rock, Illinois, world's

largest yellow fluorite); 100

4.

3.180; massive material with impurities 3.0-3.25.

Density:

locali-

fluorite crystals are transparent.

(pale blue, Korea); 263, 234 (light brown, Africa); 118

HU:

Vitreous.

Hardness:

SI:

Many

(purple, England); 354 (pale yellow, Illinois); 229, 124.5

An extremely wide range is represented: color-

Luster:

rough from a wide range of

availability of suitable

cubes, octahedra, and other forms, often twinned; also

Colors:

Fluorites can be very large because of the

Stone Sizes:

CaFi.

(chrome

fluorite,

Colombia);

30 (chrome fluorite, Azusa Canyon, Los Angeles County, California).

Perfect 4 directions. Quite brittle. Cleavage

Cleavage: is

Isotropic;

N=

Illinois).

1.432-1.434.

Comments:

0.007 (very low).

Dispersion:

its

U

and rare earths are often present; spectrum reflects their presence. Spectra usually vague, however. Green material has lines at 6340, 6100, 5820, and 4450 and a broad band at 4270. Spectral:

Luminescence: Yellow, blue, white, reddish, violet, green in LW. Fluorescence likely due to U and rare earths,

sometimes material

is

to organic inclusions (hydrocarbons).

thermoluminescent; some

Phosphoresces

in X-rays.

is

Some

phosphorescent.

Subject of luminescence and

fluorescence began with studies of fluorite.

Occurrence:

In

(pink, South Africa); 203.5 (yellow, Illinois);

17.92 (brown, Michigan); 3969 (Kashmir-sapphire blue,

octahedral, very easy.

Optics:

PC: 100+

too fragile for wear because of It is

also

on the

soft side for

range of attractive colors. Faceted gems can be extremely bright, despite the

low index of refraction, since the

material takes a high polish.

Most

of the available stones

are in the blue-violet-green range; pinks are rare as

is

the

chrome-green material from Colombia. Bicolor gems are sometimes cut from zoned crystals. An English fluorite with an alexandritelike color change (pink-blue) has been reported, as has similar material from Cherbadung,

fine

Switzerland. Large fluorites totally free of internal flaws are extremely rare.

hydrothermal deposits; sedimentary

many

is

jewelry use. Fluorite does, however, occur in a very wide

Name:

rocks; hot springs; rarely in pegmatites; usually associated

with sulfide ore deposits. There are

Fluorite

cleavage and brittleness.

easily

From

and

is

the Latin fluere (to flow) because

it

melts

used as a flux in smelting.

localities

worldwide.

New

Mexico; Colorado; Michigan. Italy; South Africa; Austria; Czechoslovakia; Germany; Korea; Africa; USSR. England: Blue John or Derbyshire Spar used for more than fifteen hundred years as decorative material in vases, carvings, bowls, and so forth. It is banded in white and shades of blue, violet, and reddish brown. Derbyshire deposits now exhausted. Also from Cumberland and

FORMANITE

See: Fergusonite.

FORSTERITE

See: Olivine.

FRIEDELITE (Mn,Fe) 8 Si60 18 (OH,Cl)4

Formula:

Crystallography:

3H 0. 2

Hexagonal (R). Crystals are tabular, and very rare. Usually mas-

needlelike, hemimorphic,

Cornwall.

Chamonix, Switzerland; octahedral pink

crystals,

on quartz,

Colors:

very rare. Illinois: best

sive, fibrous aggregates, cryptocrystalline.

known, especially

violet material

from

Pale pink to dark brownish red, red, brown,

orange-red.

FRIEDELITE

700

Luster:

brownish, cryptocrystalline and looks

Vitreous.

Hardness:

like a fibrous chal-

cedony. Seams of the material at this deposit were up to 2

4-5.

inches wide.

Kuruman, South Africa; massive dark

3.04-3.07.

Density:

Cleavage:

Perfect

Optics:

=

o

1

direction. Fracture uneven. Brittle.

1.654-1.664; e

=

Translucent stones up to 1-5 carats nor-

mal; cabochons to about 30 x 40

1.625-1.629.

mm. The

larger stones

lose any transparency.

Uniaxial (— ).

Usually refractometer shows shadow edge at about Birefringence:

Stone Sizes:

rose red.

1

.645.

Comments: rial

0.030.

Friedelite

has been faceted.

is

not abundant, and

The cabochons

little

mate-

cut from Franklin

material are lovely, rich colored, and usually translucent.

Broad band at 5560 and also 4560 spectrum not diagnostic.

Spectral: tinct);

be reddish in LW and SW. material green (SW) and yellow (LW).

Luminescence:

May

(indis-

The faceted gems are exceedingly rare and true collector Such stones are seldom seen even in large collecCabochons of material from the deep manganese mine at Kuruman, South Africa are rose-red and items.

Some

tions.

translucent.

Occurrence: In manganese deposits. Orebro, Sweden; Adervielle, France; USSR; Austria. Franklin, New Jersey: source of gem material. Usually

Name:

After the French chemist and mineralogist,

Charles Friedel.

G GADOLINITE

problems

Be FeY

Formula:

2

2

Name:

often terminated; massive.

After the Swedish chemist,

GAHNITE

J.

Gadolin.

See: Spinel.

Black, greenish black, brown, very rarely light

Colors:

GALAXITE

green.

Streak:

Greenish

Luster:

Vitreous to greasy.

Hardness:

gray.

See: Spinel.

GARNET FAMILY AsB

Formula:

6.5-7.

2

Si 3 0i2.

A=

Fe, Ca,

Mn, Mg; B =

Al, Fe,

Ti, Cr.

4.0-4.65 (usually 4.4); metamict material

Density:

The

~

garnets are a complex family of minerals,

all

having very similar structures but varying enormously

4.2.

in

chemical composition and properties.

None. Fracture conchoidal.

Cleavage:

a =

Optics:

Biaxial (+), 2

hence

1.77-1.78;

V=

y =

Garnets, for convenience, have in the past been grouped according to composition. Garnets containing Al in the B position in the formula are widely called pyralspites

Brittle.

1.78-1.82.

85°. Usually metamict and amorphous,

(acronym: PYRope, ALmandine, SPessartine) and gar-

isotropic.

Birefringence:

There

is

in

differences in internal structure. Uvarovite

tem

show

parent, even in thin splinters.

is

This

is

not a terribly attractive gemstone, a tremendous

quite brittle, but there

is

rarity.

no cleavage

(see

diagram

The formulas

Texas. This massive material cuts cabochons

gems would be

a fairly rare

of as comprising a five-component sysillustrating the general

scheme of chem-

ical substitutions).

gems, however, would be and very rare since the mineral is rarely trans-

but faceted

is

garnet with restricted occurrence; the other five garnets

to several pounds. Faceted

Comments:

position are called ugrandites

complete solid solution between certain gar-

may be thought

unearthed

A

net species, but not between others, due to specific

Stone Sizes: Norwegian crystals have been found up to 4 inches across and nodules up to 60 pounds have been

material

in the

(Uvarovite, GRossular, ANDradite).

Australia.

very tiny

Ca

nets with

High, and variable 0.01-0.04.

Occurrence: Granites and granite pegmatites. Colorado; Texas; Arizona. Greenland; Sweden; Norway; USSR; Japan; Switzerland;

up

do not know of the existence of a

I

at this writing.

Si20io.

Monoclinic. Crystals rough and coarse,

Crystallography:

in cutting.

gem

faceted

of the garnet species are listed here to

similarities.

Uvarovite:

CaiC^SbO^

Pyrope:

Grossular:

Ca3AliSi30]2

Almandine: FeiAl2Si30i2

Andradite; Ca3Fe 2 Si30i2

The

Spessartine:

MgjAhSijO^

MnjAhSbOu

Also note: Goldmanite: Ca 3 V 2 Si30i2. Tiny, dark green

to cause

707

crystals.

GARNET FAMILY

702

Spessartine

Colors:

1.78-1.81

Pyrope-Spessartine 1.742-1.78 (malaya; color change garnets)

Andradite 1.880-1.895

Uvarovite: dark green. Grossular: colorless, white, gray, yellow, yellowish green,

green (various shades: pale apple green,

medium apple

green, emerald green, dark green), brown, pink, reddish, black.

{topazolite

Pyrope1.714-1.742

Andradite: yellow-green, green, greenish brown, orangy yellow, brown, grayish black, black.

The

color

is

related

and Mn. If there is little of either element, the color is light and may resemble grossular. Pyrope: purplish red, pinkish red, orangy red, crimson, dark red. Note: Pure pyrope would be colorless; the red colors are derived from Fe + Cr. Almandine: deep red, brownish red, brownish black, to the content of Ti

Py rope- Almandine 1.742-1.785 (chrome pyrope; Grossular

Almandine

1.730-1.760

1.785-1.830

rhodolite)

[tsavorite;

hessonite)

Garnet species and ical

varieties;

shaded

lines indicate

chem-

substitutions; varieties are in italics; refractive indices

as shown.

violet red.

Spessartine: red, reddish orange, orange, yellow-brown,

reddish brown, blackish brown. Malaya

from the

-spessartine

Hydrogrossular:

CaiAMSKXh

,(OH) 4>

.

May

be a com-

ponent of grossular. Henritermierite: Cai(Mn,Al)(Si04) 2 (OH)4. Tetragonal, very garnetlike, often twinned.

Kimzeyite: Ca3(Zr,Ti) 2 (Al,SibOi 2

MgjCr

Knorringite:

Mg

Majorite:

3

2

Si 1

12 .

.

a pyrope-

colors include various shades of orange, red-orange, peach,

and pink. A well-known commercial garnet is intermediate between pyrope and almandine. It is often said that such a garnet

is

a mixture of "molecules" of these garnets,

.

Like a "chromiferous pyrope."

(Fe,Al, Si) 2 SbOi 2

is

Umba River Valley of Tanzania; the

Purple; found in a

whereas this really means its structure contains both Fe and Al. The intermediate garnet, known as rhodolite, usually has a distinctive purplish color.

meteorite!

Schorlomite: CaiTi FeiOi 2 2

Yamatoite:

The above

variations

make

it

easy to see

why

it

is

.

foolish to try to guess the identity of a garnet

MnA^SijOn.

on the

basis

of color alone!

These are mostly

rare species, but the fact that the

garnet structure type can

accommodate such

a

wide

variation in composition indicates the range of substitutions possible in natural garnets. This accounts for the

huge range of colors seen

in

the family as a whole.

Optical properties of garnets are very dependent on

Sometimes straight-line graphs are used to composition with refractive index or density. This type of graph assumes a simple additive relationship in chemical substitution and is inadequate when several substitutions occur simultaneously. In many instances a chemical analysis is needed to positively identify a garnet.

chemistry. relate

Stone Sizes:

Garnet

crystals are usually small, micro-

scopic up to about 6 inches

in the

case of grossular.

Garnets in rock, with poor external forms, may be much larger, such as the almandine from Gore Mountain, New York, which reaches a diameter of 60 cm. A few spessartines in Brazil have weighed several pounds and have retained great transparency and fine color, but these are very rare. A typical garnet crystal is about half an inch to an inch in diameter. Optics:

These are very dependent on chemistry,

as

indicated previously; the pyralspites are generally isotropic, but the presence of the large

makes them

Ca atom

in

the struc-

birefringent. Grossular

Physical Properties

ture of the ugrandites

The

and andradite are almost always zoned, often twinned, and are distinctly not isotropic in the microscope. Recent X-ray data, in fact, clearly show that ugrandites can be orthorhombic and some may even be monoclinic, perhaps as a result of cation ordering on certain crystal-

garnets have no cleavage but display a conchoidal

fracture

The

and are somewhat

luster

is

andradite, and in grossular

brittle

and tend

to chip easily.

vitreous, inclining to resinous in grossular,

some almandines. The hardness is 6.5-7.5

and uvarovite; 6.5-7

in

andradite; and 7-7.5

in the pyralspite series.

Garnets are all isometric, and crystals show the comforms in this crystal system, such as the trapezohedron and dodecahedron. Interestingly, the most common isometric forms, the cube and octahedron, are extremely rare in garnet crystals. Garnets may also be massive, granular, and in tumbled pebbles.

mon

lographic

sites.

Uvarovite Density: Optics:

3.4-3.8 (usually 3.71-3.77).

N = 1.74-1.87.

Occurrence: Chromites and serpentines, that is, metamorphic environments where both Ca and Cr are present.

Oregon.

Sri

Thetford, Quebec, Canada.

(hessonite).

Outokumpu, Finland:

known

best

locality, in large, fine,

green crystals.

GARNET FAMILY

103

gem

gravels

Lanka: grossulars are found

Wilui River,

USSR: opaque green

the

in

crystals with idocrase.

China: massive white grossular.

Norway-

Australia (Harts Range, Northern Territory): hessonite.

USSR:

New

fine crystals.

South Africa. Northern California:

chromite deposits.

in

carat, even

1

fine grossular in various colors,

especially the dark green material being marketed as

Stone Sizes: Faceted uvarovites are extremely rare because crystals are always opaque. An occasional crystal may have a transparent corner that could yield a stone of less than

Zealand: hydrogrossular.

Kenya and Tanzania:

though crystals may reach a

tsavorite, containing V and Cr. South Africa: massive green material that resembles jade. Pakistan: some faceted green gems; also massive green

grossular, various shades.

size

Brazil; Switzerland.

of 1-2 inches.

The

Comments:

color of uvarovite

ald (deep, rich green), so

cannot be cut. Uvarovite collectors.

Name:

it

is

is

a

is

like that of

shame

After Count

president of the

St.

S. S.

that crystals

a rare mineral, prized by

not generally regarded as a

It is

emer-

gem

garnet.

Uvarov of Russia, one-time

Petersburg (Leningrad) Academy.

Grossular Also known as hessonite, essonite. cinnamon stone: rosolite is

a pinkish variety from Mexico.

Hydrogrossular and massive varieties are cabochons of large size, including green shades cut as and also pink, translucent grossular. Massive white material from China has been carved. Orange and brown grossulars up to several hundred carats from the Sri Lankan gem gravels have been found; the fine cinnamoncolored stones from Quebec are clean only in small sizes, but good gems up to about 25 carats have been cut.

Stone Sizes:

Tsavorite

known

is

rare in clean

gems over

1

carat; the largest

are in the 10-20 carat range.

SI: 64.2 (orange-brown, Sri Lanka).

Density: Optics:

PC:

3.4-3.71; usually near 3.65.

N

=

1.72-1.80; usually 1.73-1.76 (with

V

=

61.5

(cameo head of

Christ, hessonite).

NMC: 23.94, 13.40, 8.50 (brownish-orange hessonite. Asbes-

1.743-1.759). tos,

Dispersion:

13.89 (yellow, oval).

AMNH:

Quebec); 4.68, 2.94 (colorless, Asbestos, Quebec).

0.027.

Comments:

None in pale-colored, faceted gems; a trace of almandine may produce a faint iron spectrum. A trace of Cr may produce a chrome spectrum in green varieties. Massive grossular may show a weak line at 4610 or a band Spectral:

Green, massive grossular from Pakistan shows a 6970 (weak) with weak lines in the orange, plus a strong band at 6300 and diffuse lines at 6050 and 5050. Orange stones may have bands at 4070 and 4030.

Grossular has a granular appearance under

the microscope, sometimes referred to as treacle, a swirled

look due to included diopside crystals and irregular streaks

boundaries. Zircon crystals are included

at grain

grossulars, as well as actinolite

at 6300.

material). So-called Transvaal jade

line at

material from South Africa.

Luminescence: Usually none in UV. All massive material glows orange in X-rays, as do many faceted gems.

on the content of grossular

is

pale

In

rocks, especially

metamorphosed, impure calcareous contact zones; also in schists and ser-

pentines; worldwide occurrence, widespread.

Eden

Mills,

Vermont:

fine

orange crystals, some gemmy,

California:

many

Asbestos, Quebec, Canada: fine orange to pinkish crystals at the Jeffrey

Mine, up

to 2 inches across,

gemmy.

Also colorless (N = 1.733). LakeJaco, Chihuahua. Mexico: large pinkish, white, and greenish crystals; color zoned concentrically, usually

opaque; crystals up

medium green

1.702, density 3.35). Transvaal jade

The

localities.

to

about 5 inches

in

diameter.

the green massive

in color. It

comes

from California, Pakistan, and South Africa. Hydrogrossular is a component of the massive grossulars. Material from New Zealand is known as rodingite (N =

neous,

localities.

New England: many

is

produce brown and green colors, and a rich green shade is due to Cr. Californite is a mixture of idocrase and

may have

a splintery

in

green, gray-

is

gray material contains zoisite. Pink material, con-

taining

Mn, has N=

1.675-1.705, density 3.27.

N= massive grossular has N =

jadelike material has

a

occurs

compact and homogefracture and waxy luster.

green, bluish, and pink colors,

with green diopside.

some

The color of grossular depends Fe and Mn. If there is less than 2% Fe, or colorless. Greater amounts of Fe

grossular, usually pale to

Occurrence:

in

and apatite (Tanzania

The green,

1.728, density 3.488. Pakistan 1

.738-1 .742, density 3.63. with

Cr absorption spectrum. Similar material from Tanzania

has TV

=

1.742-1.744, density 3.68.

Colorless grossular from Georgetown, California, has

GARNET FAMILY

704

N=

1.737, density 3.506. Yellow garnet

fluoresces orange in X-rays and also

from Tanzania

UV,

N

==

1.734,

density 3.604. Tsavorite from Lualenyi, Kenya, has

=

1.743, density

3.61 (mean).

It

is

inert in

UV

N—

light,

contains a trace of Cr and a significant amount of vana-

dium. The color of these tsavorites is therefore due to vanadium, not chromium as originally suspected. The pinkish grossular in marble from Lake Jaco and Morelos, Mexico, is variously known as xalostocite,

and

landerite,

Stone Sizes: ish

Andradite

however,

seldom faceted, but brown-

a rare but well-known gem, and

is

the most valuable of

all

is

probably

the garnets.

SI: 10.4 (USSR); also 4.1, 3.4, and 2.3. PC: 18 (sold in New York City); a California collector owns a huge topazolite (green color) that would yield faceted gems over 20 carats. This crystal weighs 1

ounce.

USSR: many

rosolite.

is

stones up to a few carats are known. Demantoid,

fine

demantoids

in

museum

collections.

Comments:

A ndradite

in jewelry,

Melanite has 1-5% Ti oxide; schorlomite also; topazolite is

from

Italy

is

is

rich in Ti

demantoid

yellowish-green;

3.7-4.1; melanite about 3.9;

demantoid

3.82-3.88.

Optics:

seen primarily

in

antique jewelry. Stones larger than 10

carats are very rare. Topazolite of fine yellow color

usually very small, and a cut

rich green, colored by Cr.

Density:

is

Demantoid was once reasonably available but since there is no current production it now

1.88-1.94; melanite: - 1.89;

demantoid:

1.881-1.888; schorlomite: 1.935; topazolite (yellow): 1.887.

Dispersion:

0.057 (large).

A strong band is visible at 4430, cutoff at the end of the spectrum. Sometimes (in demantoids) the Cr spectrum is visible, with a doublet at 7010, sharp line at 6930, and 2 bands in the orange at 6400 and 6220. Demantoid is red in the Chelsea filter. Spectral:

is

over 2-3 carats would

be rare. Black garnets have occasionally been used in mourning jewelry. Brown andradite is not a well-known

gem garnet. The dispersion

N=

gem

of andradite

is

any garnet, and gems have tremendous

the highest of

fire,

but this

is

masked by the body color. The fire is eminently visible in some paler demantoids, which makes them distinctive and much more attractive than comparably colored grossulars, which have much lower dispersion. The horse-tail inclusions are proof positive in identification. usually

violet

Luminescence: Inclusions: tail

distinguished by so-called horse-

inclusions of byssolite (fibrous amphibole); these are

diagnostic for this gem. ally

is

These inclusions

also occasion-

produce catseye gems.

Occurrence: Andradite occurs in schists and serpentine rocks (demantoid and topazolite); also in alkali-rich igneous rocks (melanite and schorlomite); and in metamorphosed limestones and contact zones (brown and green colors).

San Benito County, California: topazolite (N= 1.855-1.877, S.G. = 3.77-3.81), demantoid {N= 1.882, S.G. = 3.81), and unusual catseye material. Arizona; New Jersey; Pennsylvania. Greenland; Norway; Sweden; Uganda; Sri Lanka. Colorado: melanite. Arkansas: schorlomite. New Mexico: in metamorphic limestones and ore deposits. USSR: fine demantoid from the Urals. Also some (small)

brown andradite. Zaire: brown and green andradite, also some demantoid. Ala, Piedmont, Italy: dark apple green demantoid garnet; also topazolite (yellow).

Korea: andradite, some fine green with Cr.

Monte Somma, (black).

Vesuvius,

and

Trentino, Italy: melanite

3.65-3.87.

Density: Optics:

None.

Demantoid

Pyrope

TV

=

Dispersion:

1.730-1.766. 0.022.

Spectral:

The chromium spectrum

the far red

is

of emission lines in

absent in pyrope; however, the almandine

(iron) spectrum is often visible. Otherwise, Cr masks the almandine spectrum and we see a narrow, weak doublet at 6870/6850, with possible weak lines at 6710 and 6500. A broad band, about 1000 A wide, may be visible at 5700.

Luminescence:

None.

Pyrope contains small rounded

Inclusions:

crystals, cir-

cular snowballs of quartz crystals, and (from Arizona)

octahedra and minute needles.

and serpentine and gravels derived from their weathereclogite and other basic igneous rocks. Mexico; Arkansas; North Carolina.

Occurrence:

In peridotites, kimberlites,

rocks, and sands ing; also in

Utah;

New

Czechoslovakia; Brazil; Argentina; Tanzania; Transbai-

USSR; Bingara, N.S.W., Australia; Anakie, Queensland, Australia; Ottery, Norway. Arizona: a component of ant hills. kalia,

Umba Valley, East Africa: shows color change (see below). South Africa: in kimberlite and eclogite associated with diamond; fine color. The best known pyrope is from near Trebnitz, Czechoslovakia, the so-called

Bohemian

garnets.

The

garnets

GARNET FAMILY in volcanic breccia and tuffs and conglomerates. These garnets provided a major local industry in the

occur

nineteenth Century, but the deposits are exhausted.

enormous quantity

Pyropes of large

Stone Sizes:

size are

An

was

sold.

extremely

rare.

Many

large

of pyrope from these mines

Stones over 1-2 carats are usually very dark.

105

Almandine is usually included with a variThere are zircon crystals with haloes due radioactivity; irregular, dotlike crystals, and lumpy

Inclusions:

ety of minerals. to

crystals; rutile needles, usually short fibers, crossed at

110° and 70°; there are dense hornblende rods (espe-

from Sri Lanka); asbestiform needles of augite or hornblende that run parallel to the dodecahedral edges: cially

gems are in the Kunsthistorisches Museum in Vienna. There are stories about hens-egg-sized gems in the former Imperial Treasury in Vienna. The Green Vaults of

also apatite; ilmenite; spinel; monazite; biotite; quartz.

Dresden contain a huge gem said to be the size of a pigeons egg. Reports of a 468.5 carat gem also appear in

Almandine is a widespread constituent of metamorphic rocks; also in igneous rocks, in contact metamorphic zones, and as an alluvial mineral.

the literature.

Colorado; South Dakota; Michigan; New York; Pennsyl-

Comments: A pure pyrope (end member in the series) is unknown in nature. Pyropes always contain some almandine and spessartine components. The almandine com-

vania; Connecticut; Maine. Canada; Uruguay; Greenland; Norway; Sweden; Austria; Japan; Tanzania; Zambia. Fort Wrangell, Alaska: fine, well-formed crystals in slate. California; Idaho: star garnets. Major gem almandine sources are as follows: India: Jaipur (in mica schist); also Rajasthan and Hyderabad; some stars also. Sri Lanka: at Trincomalee, fine color and large size.

ponent can

easily

be detected spectroscopically. Large,

clean pyropes of lively color are very rare and would be very expensive.

Some pyropes show

an interesting color

change. Material from Norway (JV= 1.747, S.G. is

wine red

in

incandescent

=

3.715)

light, violet in daylight,

but

these stones are very small (about half a carat). Pyrope

from the

Umba Valley

in

East Africa

3.816) are pyrope-spessartines (with

{N = 1.757, S.G. = some Ca and Ti);

they are greenish blue in daylight and magenta in tungsten light.

They have

inclusions of plates of hematite and

rutile needles. All these

color-change pyrope-spessartines

have absorption bands

at

4100, 4210, and 4300 that

may

merge to form a cutoff at 4350. In stones with a strong change of color, a band at 5730 is broad and strong.

Gems sold as pyrope are usually almandines with a pyrope component, especially if they are of large size. The pyropes from South Africa occur with diamonds, and sometimes pyrope crystals are inclusions within diamonds. The color of these is superb, blood red, but the sizes are always very small. Malaya is a variety of pyropespessartine that varies in color from red, through shades of orange and brownish orange to peach and pink. Absorption bands are always visible at 4100, 4210, and 4300 that may merge to form a cutoff at 4350. There may also be absorption bands at 4600, 4800, 5040, 5200, and 5370. These stones are only known from Tanzania.

Occurrence:

Minas Gerais; Bahia.

Brazil:

Idaho: star garnets.

Madagascar: large

60-cm

components, and this creates a wide range of colors, including brown, red-brown, purplish red, wine red, purple, and deep red. Inclusions of asbestiform minerals (pyroxene or amphibole) create a chatoyancy that yields, in cabochons, a 4-rayed star. Star gems come primarily from Idaho and India. The Idaho material has./V= 1.808, density 4.07 (up to 4.76 due to inclusions). Inclusions in

Dispersion: Spectral:

gems vary

This

None.

is

often

Rhodolite of almandine

Rhodolite is

distinctive

and diagnostic: there is a band 200 A wide at 5760 (strong) and also strong bands at 5260 and 5050. Lines may appear at 6170 and 4260. This pattern of 3 (or sometimes 5) bands is seen in all almandines, and most garnets with a significant almandine component. Luminescence:

which

under magnification.

1.78.

0.027.

The spectrum

widely, but are usually not too obtru-

especially true of the silk,

is

visible only

above

New

so badly shattered that stones up

Comments: Almandine is perhaps the commonest garnet. Gemstones always have some spessartine and pyrope

sive.

1.75-1.83; usually

is

,

Mine,

from the fragments. Indian and Brazilian almandine constitutes the bulk of material on the marketplace. SI: 174 and 67.3 (stars, red-brown, Idaho); 40.6 (redbrown, Madagascar).

faceted

N=

known such

to only 1-2 carats can be cut

Density: Optics:

size are

crystals in rock at the Barton

York. This material

Almandine 3.95-4.3.

Almandines of large

Stone Sizes: as the

sizes.

is

intermediate

in

composition between alman-

dine and pyrope, with a ratio of Al to Fe of 2 to 2 pyrope

+

lite is in its

1

almandine).

color,

which

is

The

1

(that

is.

distinctiveness of rhodo-

nearly always a purplish red.

The absorption spectrum always shows almandine lines.

Inclusions include apatite crystals (North Carolina)

and any of the other inclusions found in almandine. The color of a garnet is misleading, and a chemical analysis is

GARNET FAMILY

706

required to show whether a garnet

is

an almandine or

pyrope, or a mixed crystal. 3.79-3.80 (Tanzania); 3.83-3.89 (Zimbabwe);

Density:

3.84-3.89 (North Carolina).

N=

Optics:

1.750-1.760 (Zimbabwe);

Gems weighing more than 100 carats have been cut from Brazilian and Madagascar rough. Amelia stones are fine color (orange) but small, up to about 15-20 carats, although crystals weighing several pounds have been found there. Stone Sizes:

SI:

109 (red, Brazil); 53.8 (red, Brazil); 40.1 (orange,

1.760-1.761 (North Carolina);

Virginia).

1.745-1.760 (Tanzania).

AMNH: 96

(reddish, Brazil

Comments:

Spessartine

Dispersion:

0.026.

— not

is

clean).

fairly rare as a

gem

garnet,

Stone Sizes:

and one of the most beautiful. Large stones are very rare, and usually quite dark. The finest color is an orangy red, as exemplified by the material from Ramona, California, and Amelia, Virginia. A red-brown tint indicates a higher content of almandine, accompanied by higher refractive

SI: 74.3, 22.1 (Tanzania); 16.5 (North Carolina).

index; pale orange colors are closer to pure spessartine.

Occurrence: North Carolina: rhododendron red, lilac, pinkish. Sri Lanka; Madagascar; India; Tanzania; Zimbabwe.

Comments: The original locality for rhodolite was Cowee Creek, Macon County, North Carolina. Stones from but

this locality are usually

new finds

in

very small (under 1-2 carats),

Africa have yielded

gems over 75

carats.

Material from the North Pare Mountains, Tanzania,

show a color change, blue incandescent S.G.

=

in

may

daylight to purplish red in

light, similar to

alexandrite

(N =

Spessartine as a lively

component

of almandine tends to

add a

reddish tinge of color.

Unusual color-change garnets with large amounts of and Cr have been reported from East Africa. These are primarily spessartine, with an unusually large component of grossular. The color change may be as follows:

V

1.

greenish yellow-brown (transmitted fluorescent light)

1.765,

to purplish red (reflected fluorescent); reddish orange

3.88).

to red (incandescent light)

N=

1.773, S.G.

=

3.98;

spessartine/grossular/almandine. Spessartine Density: Optics:

3.8-4.25;

N=

gems

2. light

bluish green (transmitted fluorescent) to purple

usually 4.12-4.20. (reflected); light red to purplish red (incandescent)

1.795 (Amelia, Virginia).

but a stone of 24.87 carats was sold in 1979.

ally small,

0.027.

The

Mn

spectrum is evident: lines at 4950, 4850, 4620 (all weak) and strong lines at 4320, 4240 (weaker), and 4120 (intense). Almandine may be present, contributing lines at 4320 and 4120. Spectral:

Luminscence: Inclusions:

None.

Wavy

feathers,

due in

to liquid

drops that

gems from

Sri

Lanka

Brazil.

Carolina.

(fine

crystals, especially

orange gems).

Amelia Court House, Virginia: fine orange to deep brownish material, gemmy. Norway; Tsializina, Madagascar. Sri Lanka and Burma: in the gem gravels.

and Ceara): large pounds), gemmy, fine color.

Brazil (Arassuahy eral

pomegranate Uvarovite

fruit.

named

is

Grossular

name

is

crystals (up to sev-

St.

after

Count

S. S.

Uvarov, one-time

Petersburg (Leningrad) Academy.

named

after R. grossularia, the botanical

for the gooseberry,

because of the resemblance of

the color (pale green) to that of the plant.

of

its

from a Greek word meaning

is

inferior

because

lower hardness.

Tsavorite

is

named

after the

Tsavo National Park

in

occurrence

in

Kenya. Californite

San Diego County, California: good

Ramona

garnet grains in rock with the scattered dark seeds of the

Hessonite

Occurrence: In granite pegmatites; also gneiss, quartzite and rhyolite, and sometimes as a component in skarns. Nevada: Colorado; New Mexico; Pennsylvania; North

at

Names: Garnet comes from the Latin word granatus, meaning grain. This originated in the comparison of

president of the

have a shredded look, especially

and

N=

3.89; spessartine/grossular/pyrope.

So-called alexandritelike garnets have also been noted, changing from violet-red to blue-green. These are usu-

1.803-1.805 (Brazil).

Dispersion:

=

1.763, S.G.

1.79-1.81;

is

named

after the original

California.

Andradite is named after the Portugese mineralogist d*Andrade, who described one of the subvarieties of this species. Topazolite is named after its resemblance to yellow topaz. the French demant (diamond) because of the brilliance and luster. Melanite comes from the Greek melanos (black).

Demantoid comes from

GRANDIDIERITE Pyrope comes from the Greek word lot firelike,

in allu-

sion to the red color.

Almandine in

is

a corruption of the locality

name Alabanda,

came

the red garnets

from the Greek rhodon,

is

gems

Name: J.

described by Pliny.

its

cut. Transparent crystals are not terribly rare, but

faceted

Asia Minor, from which place

Rhodolite

been

After the eminent French chemist, Professor L.

Gay-Lussac.

GLASS: is

named

See: Obsidian.

after the locality Spessart, in North-

GOLDMANITE

west Bavaria (Germany).

Malaya is a Bantu word meaning "out of the sometimes said to mean "deceiver."

See: Garnet.

family,"

GOSHENITE

See: Beryl

GRANDIDIERITE

GAYLUSSITE

(Mg,Fe)Al,BSi0 4

Formula:

5H 0.

NajCafCCb

Formula:

are relatively uninteresting.

rose, in allusion to

color.

Spessartine

Orthorhombic. Crystals elongated and

Crystallography: flat-

tened, and wedge-shaped.

Colors:

Colorless, white, grayish, yellowish.

Luster:

Vitreous.

Colors:

Blue-green; translucent.

Luster:

Vitreous.

Hardness:

7.5.

Density:

2.85-3.0.

1.995.

Cleavage:

Perfect

1

direction. Fracture conchoidal.

Cleavage: Optics:

Brittle.

Biaxial

not well formed; massive.

2.5-3.

Density:

a =

Optics:

.

2

Monoclinic. Crystals elongated,

Crystallography:

Hardness:

107

1.445;

(),2K=

fl

=

1.516;

y=

Perfect

a=

Biaxial (-), 2 1.522.

Pleochroism:

direction,

1.583-1.602;

V=

/?

=

good

1

direction.

1.618-1.636;

y=

1.622-1.639.

30°.

=

(Madagascar stone: a

34°.

Birefringence: Birefringence:

1

1.583;

y =

1.622; S.G.

=

2.85).

0.039.

0.077.

Strong: dark blue-green/colorless/ dark

Pleochroism:

None.

green.

Not diagnostic.

Spectral:

Not diagnostic.

Spectral:

Weak cream

Luminescence:

May

white

in

SW

(Nevada).

be triboluminescent.

Occurrence:

Luminescence: Occurrence:

In alkaline lakes or evaporite deposits

None.

Generally

in

pegmatites.

Andrahomana. South Madagascar: only well-known

rich in borax.

California: Searles Lake,

Owens Lake, China Lake, Borax

locality.

Stone Sizes: Cut as cabochons up to about inch 1-10 carats). At best, the material is translucent, and generally is opaque.

Lake.

1

Wyoming; Nevada. Mongolia, China. Venezuela:

Kenya:

in

in clay beds.

transparent crystals, from Lake Amboseli.

Comments:

Crystals from Searles Lake have been found up to 2 inches long. Gems cut from such crystals could be up to about 20-30 carats.

Stone Sizes:

Comments:

This mineral is very hard to cut because of extreme softness and cleavage. Gaylussite dries out slowly in air

and the surfaces may turn white. Stones

prevent dehydration. Gaylussite

is

seen only

relatively

a rather rare mineral, with

never transparent enough

to facet, but attractive, sometimes even jadelike cabochons are cuttable from the translucent material. The

high hardness makes

it

suitable for wear, although cut-

have to pay close attention to the cleavage. Cut grandidierite is seldom seen in collections because few ters

collectors have even heard of

it

or

know

it

exists in

in collec-

tions are therefore best stored in sealed containers to

comprehensive collections, and

is

It is

Grandidierite

a lovely blue-green color.

(

in

very

few stones have

cuttable form.

Name:

After Alfred Grandidier, a French explorer,

who

described the natural history and geography of Madagascar.

GYPSUM

108

GROSSULAR

Mexico:

See: Garnet.

at Naica,

Chihuahua,

in

enormous

crystals to 6

feet long.

GYPSUM

Also known as Alabaster; variety Satin Spar.

CaS0

Formula:

'

4

2H 0.

Italy.

2

Monoclinic. Crystals often perfect and

Crystallography:

Braden, Chile: crystals reported up to 10 feet long.

Alabaster from England; Tuscany,

large; tabular; rosettes; lenticular; helictites are gro-

tesque shapes found

often twinned; massive;

in caves;

granular.

Massive gypsum

Stone Sizes:

in

any desired

size (for

cabochons and carvings). Fibrous material cut into large carvings, up to several pounds. Faceted gypsum could be up to hundreds of carats, as large transparent crystals exist.

Colorless, white, gray; impurities

Colors:

yellowish, reddish, brownish, greenish.

and patterned

like

make

it

Sometimes banded

erals

marble.

Gypsum

Comments: and

is

is

one of the most abundant min-

found especially

in

evaporite environments.

Alabaster, the massive, granular variety, has been used

Subvitreous; pearly on cleavages.

Luster:

Hardness:

thousands of years, made into vases, bowls, and other and decorative objects. Today it is used in ashtrays, clock housings, paperweights, and so forth. for

useful

2.

2.32 (range 2.30-2.33).

Density:

Perfect and easy,

Cleavage:

1

direction distinct 2 other ;

dling carvings

directions.

a =

Optics: Biaxial

Gypsum can be scratched by the fingernail, much too soft for hard use. Care must be taken

1.520;

(+),2V=

Birefringence:

Dispersion:

fi

=

1.523;

y =

Selenite

58°.

easily.

the term applied to colorless, transparent

crystals. Satin

spar

is

used to describe massive fibrous

varieties that are often cut into

0.010.

cabochons or carved

Faceted gypsum

None.

is

not often seen since cut stones are

unattractive and very difficult to fashion,

Not diagnostic.

Spectral:

ish

white

in

UV.

Occurrence:

Inert in X-rays.

In sedimentary rocks

due

material.

Name: and deposits;

saline

to

Gypsum from the Greek gypsos,

what we now

call plaster. Satin

spar

a

name applied

in allusion to the

from the moon, due to the pearly luster on cleavage surfaces. Alabaster from the Greek word alabastros, a stone from which ointment vases were made.

lakes; oxidized parts of ore deposits; volcanic deposits.

satiny luster of the fibrous material. Selenite

Utah; Michigan; Colorado; South Dakota; New Mexico;

Greek word

New

York; Kansas; other states.

California;

many

locations.

to the

exceptionally perfect cleavage and low hardness of the

Sometimes indistinct brownish or green-

Luminescence:

into

animal shapes. This material has a great chatoyancy, and brown-colored satin spar makes lovely decorative items.

0.033.

Pleochroism:

is

it is

han-

and useful objects, but scratches can be

polished out rather 1.530.

so in

for

H

HACKMANITE

See: Sodalite.

are very rare. In 1968 a dealer offered a white stone of

28.86 carats, however.

PC; 40.20

HAMBERGITE

Comments:

Be BO,(OH,F).

Formula:

2

Hambergite

unusual, although

Orthorhombic. Crystals prismmatic,

Crystallography:

(largest reported); also 7.6, 5.93.

it

is

is

a

gem

for collectors of the

hard enough for wear.

The remark-

able properties of this material are noteworthy the lowest

flattened.

known

density for any

gem

—

it

has

of such high

makes and may

birefringence. This combination of properties

Colors:

Colorless, white, grayish white, yellowish white.

Vitreous to

Luster:

Hardness: Density:

2.35-2.37. 1

Name:

After Axel Hamberg, Swedish mineralogist,

direction. Fracture conchoidal to

called attention to the mineral.

=

HANCOCKITE

a =

1.55;

(+),2V=

Birefringence:

/3

1.59;

y =

1.63.

Spectral:

HAUYNE

0.072.

Sodalite Group: See Lazurite. (Na,Ca)4-8(Al6Si6)024(S04,S),- 2

.

0.015.

Crystallography:

Not diagnostic.

Inclusions:

weak pink-orange Occurrence:

in

in

LW

most specimens; sometimes

up

to 2

and

Luster:

x

1

and

alkali

pegma-

Hambergite

is

Slightly bluish to colorless.

Hardness: Density:

a fairly rare mineral,

5.5-6.

2.40-2.50. (Eifel

Cleavage:

uneven.

transparent enough to facet. Cut

Vitreous to greasy.

Streak:

inch.

An/anabanoana, Madagascar: large gemmy crystals. Non-gem material from Kashmir, India; Czechoslovakia; Ramona, California; Langesundsfjord, Norway. Stone Sizes:

red. Translucent to semitransparent.

(Norway).

In syenite pegmatites

crystals

Blue; also white, shades of gray, green, yellow,

Colors:

None

Isometric. Crystals dodecahedral or

octahedral; usually rounded grains.

Tubes.

Luminescence:

dom

See: Epidote.

87°.

Formula: Dispersion:

tites, in

who

Brittle.

Optics: Biaxial

Perfect

little fire

resemble quartz, but the birefringence is much larger than that of similar-appearing gemstones. Usually cut stones are not clean, but filled with cleavage traces.

dull.

7.5.

Cleavage:

uneven.

identification fairly easy. Stones have

Distinct

1

=

2.40.)

direction. Fracture conchoidal to

Brittle.

sel-

gems over 5 carats

Optics:

709

N=

1

.496-1 .505. (Eifel

=

1

.502.)

7

HAWK'S EYE

70

A

Occurrence:

Not diagnostic.

Spectral:

Luminescence: Usually none; sometimes orange-red in LW (Germany).

major ore of

iron; usually in

morphic rocks, and lavas (deposited from vapor). Lake Superior region, Minnesota; Michigan; Wisconsin;

Occurrence: Alkaline igneous rocks, associated with leucite and nepheline. Montana; South Dakota; Colorado. Quebec, Canada; France; Laacher See, Germany; Italy;

New

Morocco.

Brazil: fine crystals, also massive material

Stone Sizes: Opaque material is cut into cabochons up to an inch or two, but faceted gems are exceedingly rare and always small (under 1-2 carats), chiefly from the Eifel region of

Comments: lapis lazuli,

West Germany. is

however, rarely seen as a distinct

gem species.

collectors mainly as a curiosity, but faceted

cut for

It is

gems that are

deep blue in color are extremely beautiful. Blue most sought after color in this material.

Name:

York; Alaska; Tennessee; Pennsylvania; Missouri; South Dakota; Wyoming; Arizona. Elba, Italy; Canada; Mexico; Cuba; most European countries.

is

the

After Rene Just Haiiy, one of the great early

locality

England: kidney ore from Cumberland area.

Hematite

Stone Sizes:

is

almost always opaque, usually

desired size. Massive material

is

available in very large

and good for cutting. Opaque submetallic gems are also sometimes faceted in the nature of marcasite, with a flat base and a few facets. pieces, solid,

Comments: and others

Hematite was used by the American Indians as a face paint (so-called red ochre).

compound known

The

on and gold, is powdered hematite. The streak is characteristic and diagnostic. Hematite is a weak electrical conductor, as opposed to psilomelane, a similarappearing manganese oxide. Much hematite is cut in Idar-Oberstein, Germany, but the material comes from England. Hematite is simulated by a variety of materials. polishing

as rouge, used widely

silver

mineralogists.

HAWK'S EYE

See: Quartz.

HEDENBERGITE HELIODOR

See: Diopside.

One

See: Beryl

HELIOTROPE

HEMATINE

is

See: Quartz.

known

as hematine,

is

a mixture of stain-

with sulfides of Cr and Ni.

It

has a red streak but

of these,

less steel

quite magnetic, whereas hematite

is

not.

Hematine

is

made into intaglios and cameos. Hematite crystals that may be transparent are far too thin to cut, so faceted

See: Hematite.

stones are unknown.

A

massive material consisting of a

mixture of hematite, martite, and gangue minerals occurs

HEMATITE

near Ouro Preto, Brazil.

Formula:

from a

near Ouro Preto.

cut into beads, cameos, intaglios, and carvings of any

one of the major constituents of a well-known and ancient gem material. It is, Haiiyne

sedimen-

tary deposits in thick beds; also in igneous rocks, meta-

Fe203.

Hexagonal

Crystallography:

The

material

is

granular and has

a dark brown, rather than a red, streak. (R). Crystals in

wide

ety of forms, often lustrous or tarnished. Massive;

vari-

com-

Name:

From

the

Greek hema

(blood),

streak (powder) and appearance of

due

to the red

some specimens.

pact; fibrous; reniform (kidney ore); micaceous; stalactitic;

earthy.

Colors: crystals.

Steel gray to black;

Massive material

Streak: Luster:

ceous

Deep

is

blood red in thin brownish red.

HEMIMORPHITE slivers

or

red or brownish red.

Density:

Metallic, submetallic, dull; glistening in mica-

Optics:

Luster:

None. Fracture even to subconchoidal.

=

3.22; e

=

Uniaxial (— ). Birefringence:

H

2

0.

Orthorhombic. Crystals tabular and

fan-shaped aggregates.

White, colorless, pale blue, greenish,

gray,

yellowish, brown.

4.95-5.26.

o

thin, striated;

Colors:

5-6.5.

Cleavage:

2

Crystallography:

variety.

Hardness:

Zn 4 Si 07(OH)2

Formula:

2.94.

Brittle.

Vitreous, silky; dull.

Hardness: Density:

Cleavage: 0.280.

4.5-5. 3.4-3.5.

Perfect

subconchoidal.

1

Brittle.

direction. Fracture even to

HODGKINSONITE Optics: Biaxial

(

a - 1.614; /} = + ), 2 V= 46°.

Birefringence:

1.617;

y =

Luminescence:

None.

violet in

A

Occurrence:

Occurrence:

secondary mineral

in

the oxide zones

the southwestern United States and

Mexico; various localities worldwide. Mexico: crystals up to several inches in length are found at Mapimi, Durango, and Santa Eulalia, Chihuahua; some of these are transparent and will yield stones up to ~ 7-10 carats. Also found as blue crusts. Blue massive material cut as cabochons

Stone Sizes:

to several inches in length. Colorless material in

gems

faceted

DG:

Hemimorphite

gemstone. Suitable material thus

from Mexico

1-3 carats; larger stones are very rare.

1.90 (colorless, Mexico).

Comments: far.

The massive

is

is

very rare as a faceted

known

blue material

only from Mexico is

a very delicate

is seldom cut because not very much has appeared on the market.

In allusion to crystal forms.

HENRITERMIER1TE

LW

and SW; also pale

in

in

X-rays with persistent

Late stage hydrothermal mineral

in gran-

Hampshire.

Germany; Austria; USSR. Maine: colorless and pale yellow crystals. Minas Gerais. Brazil: crystals up to nearly fist size, colorless and pink; some green, violetish. Stone Sizes: Faceted gems from Maine are usually small 1-5 carats) and pale colored or colorless. Brazil gems, however, have stronger color and may be up to 25-30 carats from larger crystals. (

SI: 5.9 (green, Brazil).

DG:

3.65 (blue, Brazil).

4.65 (light violet octagon, Brazil).

Comments:

Herderite

is

a rare collector gem, especially

too soft for wear but

in larger sizes. It is

is

attractive

when

Clean stones are very hard to find. There is always the possibility of new and larger material coming on the market from Brazilian sources. cut.

Name:

After S. A. W. von Herder, a mining official

in

Freiburg, Germany.

See: Garnet.

HESSONITE

HERCYNITE

in

green gem) and stronger violet

pegmatites.

NMC:

color, but

Name:

ite

New

of ore deposits.

Found throughout

Pale green

(Brazil,

phosphorescence.

None observed.

Luminescence:

SW

LW. Orange fluorescence

Not diagnostic.

Spectral:

or weak.

Not diagnostic.

Spectral:

0.022.

Pleochroism:

None

Pleochroism:

1.636.

111

See: Garnet.

See: Chromite, Spinel.

HETEROSITE

See: Purpurite.

HERDERITE CaBeP0

Formula:

4

HIDDENITE

(F,OH).

Monoclinic. Crystals stout or prismatic;

Crystallography:

See:

Spodumene.

HODGKINSONITE

tabular; crusts.

MnZn

Formula:

2

SiO s

H

2

0.

Colorless, pale yellow, greenish white, pink,

Colors:

Monoclinic. Crystals pyramidal or

Crystallography:

pris-

green, violet.

matic; massive; granular. Luster:

Vitreous.

Hardness: Density:

Colors:

Bright pink to reddish brown, purplish pink.

Luster:

Vitreous.

5-5.5.

2.95-3.02.

Hardness:

Cleavage:

Density: Optics:

a=

Biaxial (-), 2

with (OH)

4.5-5.

Interrupted. Fracture conchoidal. Brittle.

is

Note: Green

1.591-1.594;

V= 67-75°.

= 1.611-1.613; y = 1.619-1.624. Can be (+). In general: herderite /3

+ ), with F is (-). gem from Brazil: a =

Perfect

1

direction. Fracture conchoidal.

Brittle.

(

1.581

;/3

=

1.601;

1.610; birefringence 0.029; S.G. 3.02; contains

Birefringence:

Dispersion:

Cleavage:

3.91-3.99.

0.029-0.030.

0.017.

7%

y=

F.

Optics: Biaxial

a = 1.720; /) = {-),2V= 52°.

Birefringence:

Pleochroism:

1.741;

y =

1.746.

0.026. Distinct: lavender/colorless/lavender.

HOLTITE

112

HORNBLENDE

Not diagnostic.

Spectral:

Luminescence:

Dull red in LW.

Occurrence:

metamorphosed limestone

In

New Jersey

lin,

with various other

Individual crystals reached

up

to several inches thick.

% inch The

HOWLITE Zn and Mn in

at Frank-

diameter,

in

veins

material was mined out

Stone Sizes: Cut gems are very small, less than 2 carats. This is an exceedingly rare material, available from only

5

5.

Monoclinic. Crystals

Crystallography:

tiny; usually

nod-

ular masses, chalky or porcellaneous.

Colors:

White, opaque except

Luster:

Subvitreous.

in tiny grains.

3.5 or less.

'

0.89.

Density:

Comments:

is one of the rarest of all Cut stones are bright and richly colored, but the crystals were never abundant and still fewer had transparent areas. Fewer than 10 cut stones may exist.

Hodgkinsonite

Name:

who

After H. H. Hodgkinson of Franklin,

New

2.45-2.58.

Smooth and even

Cleavage:

collector gems.

sey,

2

Hardness:

and only from older specimens.

locality

Ca B Si0 9 (OH)

Formula:

minerals.

years ago.

one PC:

See: Actinolite, Pargasite, Amphibole.

Optics: Biaxial

a = 1.583-1.586; (— ), 2 V large.

Birefringence:

Al 6 (Ta,Sb,Li)[(Si,As)0 4 ]3(B03)(0,OH)3 + Fe, Be, Ti, Mn, and Nb. Related to dumortierite. Formula:

white, buff, olive green, brownish.

Density:

Optics:

1

Birefringence:

Spheres up to about 8 inches

=

1.756-1.759;

y=

1.758-1.761.

=49-55°.

ing in turquoise. Howlite ble turquoise,

Name: Dull orange in SW, bright yellow in LW.

Occurrence: Alluvial tin deposit near Greenbushes, Western Australia, associated with cassiterite.

Could yield cabochons up

to

about

1

inch.

Comments:

This mineral was first noted in 1937 but was not described in detail until 1971. It has not yet been seen as a gem, but the high hardness would allow it be worn with no risk of scratching. Holtite is now considered to be a variety of dumortierite. The mineral comes locality,

considered a great

Name: tralia

is it

and

is

frequently dyed blue to resem-

it

makes a most convincing simulant.

is

relatively unexciting in

appearance.

Distinct: yellow/colorless/colorless.

Luminescence:

from the one

diameter

contains black, threadlike impurities resembling the vein-

The white material

Stone Sizes:

in

Howlite is always opaque in nodules; it an abundant material and easy to acquire. Sometimes

0.015.

Pleochroism:

in

Scotia: small nodules.

Comments:

direction.

1.743-1.746;/?

Biaxial (-), 21/

Microscopic crystals or nodules occur

stones.

Good

a=

Califor-

have been cut; also seen as cabochons and tumble-polished

3.90.

Cleavage:

SW; some

California: abundant nodules, up to a weight of several hundred pounds, as at Lang in Los Angeles County. Also occurs in the Mohave Desert, California.

Stone Sizes: 8.5.

in

arid regions or borate deposits.

Nova Hardness:

1.605.

None.

Luminescence: Brownish yellow nia material deep orange in LW. Occurrence:

Orthorhombic. Compact pebbles of acicular crystals, 2-15 mm diameter. Needles often in parallel arrangement. Crystallography:

Dull to resinous.

y =

Not diagnostic.

Spectral:

Luster:

1.596-1.598;

0.022.

Pleochroism:

HOLTITE

Cream

=

Jer-

discovered the mineral.

Colors:

/}

fracture.

and a cut stone would have

to

be

rarity.

After Harold E. Holt, prime minister of Aus-

from 1966 to 1967.

After H.

imately the

How who described a mineral of approx-

same composition.

HUEBNERITE

MnW0

Formula:

Crystallography:

4

Series to Ferberite:

FeW0

4.

Monoclinic; crystals prismatic;

flattened; tabular, often striated in direction of elongation.

Often

gates.

in crystal groups, radiating

Commonly

Colors:

Brownish black, yellowish to reddish brown, brown, blackish to greenSometimes color banded; sometimes tarnished

red. Streak yellowish, reddish ish gray.

iridescent.

Luster:

or parallel aggre-

twinned.

Submetallic to resinous.

HUMITE GROUP Hardness:

These minerals are

4-4.5 (increases with iron content).

in a very distinctive

Cleavage:

Perfect in

1

way:

direction; fracture uneven; brittle.

Mg(OH,F)

2

Chondrodite: Mg(OH,F)

2

Norbergite: Optics: Biaxial

(

a = + ).

2.

Birefringence:

17-2.20;

-

/}

y =

2.22;

2.30-2.32.

0.13.

orange-red/bright red; olive green/brick-red/dark red.

Not diagnostic.

Luminescence:

quartz veins

in

Ti0

2

2

(Si0 4 )

2Mg (Si0 4 3Mg (Si0 4Mg (Si0 2

)

2

4)

2

4

)

present in humite and clinohumite strongly affects

their optical properties. All

members

of this group have

poor cleavage and vitreous luster. All are generally yellowish brown in color.

biaxial

(

+ and )

Luminescence: Usually inert in SW, sometimes golden yellow; dull orange to brownish orange in LW.

None.

High-temperature hydrothermal ore veins;

Occurrence:

Mg

Humite: Mg(OH,F) 2 Clinohumite: Mg(OH,F) 2

Pleochroism: Varies with locality and iron content: bright yellow/orange-red/orange-red; greenish-yellow/

Spectral:

confused with each other as

The compositions are related

they have similar properties.

7.12-7.18 (increases with iron content).

Density:

easily

113

or near granitic rocks;

Many

localities in

New

western United States (Colorado; Idaho; Nevada;

Occurrence:

In contact

zones

in

limestone or dolo-

mite. Rarely in alkaline rocks of igneous origin. This

paragenesis

true for

is

all

members

of the humite group.

Mexico; Arizona; South Dakota).

Wiberforce. Ontario, Canada.

France; Czechoslovakia; Australia.

Tilly Foster Mine. Brewster, New York; fine crystals of chondrodite, reddish brown, some rather gemmy, associated with humite and clinohumite. This locality is the source of most gem chondrodite. Kafveltorp, Orebro, Sweden: yellowish material.

Pasto Bueno, Peru: transparent crystals.

Stone Sizes:

Huebnerite

is

transparent, and opacity

increases with iron content. Material suitable for faceting

occurs

in

Peru, and stones of several carats

in

may

weight

Pargas, Finland: yellowish material.

be cut but tend to be dark.

Comments:

should not be difficult to find numerous small faceted huebnerites among larger gemstone colIt

lections. Certainly

ample material

number

exists to cut a

Loolekop, East Transvaal:

in a carbonatite.

Norbergite from: Franklin,

New Jersey; Orange

New

Clinohumite from: California: Ala.

of such gems, although they are rarely offered for sale.

Lake

Name:

Stone Sizes:

After Adolph Hiibner, a metallurgist from

Freiburg, Saxony (Germany). Ferberite was

named

after

Baikal,

Italy;

Cut humites are always small, generally

HUMITE GROUP Members

extremely rare.

Crystallography Colors

orthorhombic yellowish tan

Chondrodite monoclinic brown,

yellow,

Density Optics a fi

y

2V Birefringence

Pleochroism a

Comments:

Faceted chondrodite

Humite

Lsiinonuuiiie

orthorhombic yellow,

deep

orange

red

Hardness

in

the 1-3 carat range. Crystals tend to be dark and filled

with inclusions and fractures. Larger cut

Norbergite

Malaga. Spain;

USSR.

Rudolph Ferber, of Gera, Germany. of this group include Humite, Clinohumite, Norbergite, and Chondrobite.

County,

York; Norberg, Sweden.

is

gems would be

almost unknown, a

ri /onoi lUoonj

monoclinic brown.

yellow,

white

6.5

6.5

6

6

3.15-3.18

3.16-3.26

3.20-3.32

3.17-3.35

1.563-1.567 1.567-1.579 1.590-1.593

1.592-1.615 1.602-1.627

1.629-1 638

1.631

1.621-1 .646

1.607-1.643 1.639-1.675 1.639-1.675

1.662-1.643 1.662-1.674

1.639-1.647 1.668

44-50°

71-85° 0.028-0.034

65-84°

73-76°

0.029-0.031

0.028-0.041

0.026-0.027 pale yellow

P

very pale yellow

y

colorless

very pale yellow/ brownish yellow

yellow

colorless/ yellowish green colorless/ pale green

colorless/ pale yellow colorless/ pale yellow

golden yellow/

deep reddish yellow pale yellow/ orange yellow pale yellow/ orange yellow

0.037

,

7

HUREAULITE

74

pity since the color is very rich and the material is hard and durable enough for wear. Cutting presents no great difficulty, but rough is virtually unobtainable, and only tiny stones could be produced. The same is true for norbergite and humite. The exception seems to be clinohumite from the Pamir Mountains in the USSR. Crystals occur there in sizes allowing the production of small (1-3 carats), slightly brownish yellow but flawless gems. This material fluoresces slightly orangy yellow in SW. Only a handful of gems have been cut.

Chondrodite from the Greek chondros, a grain

Names:

granular nature. Humite

in allusion to the mineral's

named

Abraham Hume, an

after Sir

gems and minerals of the nineteenth is

named

is

found. Clinohumite

after the locality at is

chons.

No

faceted

facetable material likely exists and one day will be cut.

The

Comments: eral is

is

color's are rich

and

too soft for wear. Hureaulite

is

lively,

but the min-

a collector

gem and

very rare even in cabochon form.

Name:

After the locality, Hureaux, France.

HURLBUTITE Formula:

CaBe2
is

English collector of century. Norbergite

Norberg, Sweden, where

Massive material suited only for cabogems have been reported to date, but

Stone Sizes:

it

the monoclinic end of the humite-

Orthorhombic; crystals prismatic,

Crystallography:

chunky, with etched surfaces and Colors:

striations.

Colorless to greenish white;

may be

stained

yellow. Streak: white.

-clinohumite series.

Vitreous to greasy.

Luster:

HUREAULITE

Mn

Formula:

5

Hardness:

(PO < )2|(P0. )(OH)]2 1

4H

2

0.

Density:

Monoclinic. Crystals prismatic up to

Crystallography:

None; fracture conchoidal;

a =

Optics: Pale rose, violet-rose, yellowish, red-orange,

2.88.

Cleavage:

3 cm, tabular; massive; compact.

Colors:

6.

1.595;

/J

=

1.601;

y =

brittle.

1.604.

Biaxial (— ).

orange-red, brownish orange, yellowish to reddish brown,

Birefringence:

gray, colorless.

Luster:

Density:

Optics:

Luminescence:

3.19.

Good

a=

Biaxial (-),

Not diagnostic.

Spectral:

3.5.

Cleavage:

1

direction. Fracture uneven. Brittle.

1.637-1.652;

/J

=

1.645-1.658;

y=

1.649-1.663.

None

reported.

Occurrence: In pegmatite with muscovite, albite, and other minerals at the Smith Mine, Chandler's Mill. Newport. New Hampshire.

2^=75°. Stone Sizes:

Birefringence:

0.012.

Pleochroism: yellow-brown. Spectral:

None.

Pleochroism:

Vitreous to greasy.

Hardness:

0.009.

This

is

an extremely rare mineral, and

small clean cuttable fragments have yielded minute faceted

colorless/pale rose to yellow/reddish

stones.

They

are transparent

and

colorless,

Name:

Not diagnostic.

under

1

After Cornelius Hurlbut, well-known professor

of mineralogy at Harvard University.

Luminescence: Occurrence:

all

carat in size.

None.

In phosphate masses in granite pegmatites.

Branchville, Connecticut; North Groton,

HYALITE

See: Opal.

New Hampshire;

HYDROGROSSULAR

South Dakota.

See: Garnet.

Haute Vienne, France; Portugal; Germany; Poland. Pala, California;

orange masses.

HYPERSTHENE

See: Enstatite.

)

ICELAND SPAR

IDOCRASE Formula:

See: Calcite.

Density:

Cu, Cr, Mn, Na, K, Ti,

Variable depending on paragenesis and min-

Optics:

(0,OH,F) 8 + Be, B, H 2 0, U, Th, Zn, Sn, Sb, 7

eral associations.

Uniaxial ( + ) or (— ); sometimes anomalously biaxial (—

rare earths.

or ( +

Environment

);

twinned.

Birefringence

e

Serpentinites

1.705-1.750

1.702-1.761

0.018

Contact metamorphic rocks

1.655-1.733

1.674-1 737

0015

Alkalic rocks

1.655-1.727

1.715-1.731

0.004

697-1.698

1.705-1.707

0.008

Regionally

metamorphosed rocks

Asbestos, Quebec,

Canada

Quebec, Canada

1

e

o

Birefringence

green emerald green

1.704 1.717

1.708

brown

1.711

mauve

1.703 1.705

1.714 1.704 1.710

0.004 0.004 0.003

Color

Locality

Laurel,

None. Fracture conchoidal.

Cleavage:

Alternative name: Vesuvianite.

Ca„Al4Fe(Al,Mg,Fe)8Si 18

3.32-3.47.

brownish yellow

1.721

Comments

contains

0.001

Mn

0.005

Note: Antimonian idocrase from contact metamorphic rocks, greenish-yellow grains, e = 1.758-1.775, o =

Incredible array of elements substitute in the idocrase

:

structure.

1.775-1.795; birefringence 0.017-0.025;

Crystallography:

Sb 2

3

>15%.

Tetragonal. Crystals often well formed,

prismatic, pyramidal, often with

0.019-0.025.

Dispersion:

complex modifications;

Pleochroism:

granular, massive. Often intergrown with grossular.

Usually weak

in

same colors

as crystal.

Also green/orange and green/yellow-green (from Quebec).

Colorless, green (various shades), brown (various shades), white, yellow (various shades), red, brown-

Colors:

ish red, blue, blue-green, pink, violet.

Spectral:

Sometimes color

Strong line at 4610, weak at 5285.

Luminescence:

None.

zoned. Luster:

Occurrence: Serpentines and related rocks; contact metamorphic deposits, especially in limestones and dolo-

Vitreous to resinous.

Hardness:

mites; alkalic rocks; regionally

6-7.

775

metamorphosed

rocks.

INDERITE

116

Finland; Japan; Korea; Tanzania.

Name:

Arkansas.

mixed/appearance, because idocrase crystal forms resem-

brown and green crystals. Switzerland: brown crystals; also

Tyrol,

on other species. Vesuvianite from Mt.

ble those seen

California: californite; also crystals at Pulga.

Vesuvius, where the mineral occurs in small, perfect

Ala, Piedmont, Italy: fine Zillerthal,

From the Greek words idos and krasis, meaning

I

at

crystals.

Zermatt, other locations.

Canada: bright yellow grains and masses. York (xanthite): brown crystals, large; sel-

Laurel, Quebec,

New

Amity,

dom

cut.

INDERITE

Mg

Formula:

Telemark,

Norway

Also known as Lesserite; dimorph of

Kurnakovite. 2

15H 0.

B„Oi,

2

(cyprine): fine blue masses with pink

Monoclinic. Crystals prismatic, up to

Crystallography:

thulite.

X

cm; nodular; acicular

Asbestos, Quebec, Canada: superb crystal groups and

10

masses, apple green, sometimes colored deep green by

Colors:

Colorless; massive varieties white to pink.

Luster:

Vitreous; pearly

1

crystals also.

Cr or pink by Mn. Kenya: green and brown

crystal fragments suitable for

faceting.

Hardness:

on cleavage.

2.5.

Sanford, Maine: brown and green crystals and masses.

Wilui River,

USSR: green

crystals

(known

Density:

as wiluite).

Morelos, Mexico: green crystals associated with pink

1.78-1.86.

Cleavage:

Perfect

1

direction. Fracture uneven. Brittle.

grossular in lake bed.

Quetta, Pakistan: fine green crystals;

some

transparent.

Optics: Biaxial

Stone Sizes: Crystals up to several inches in length occur at a few localities, but these are seldom transparent except in small areas. The maximum expectable size for a faceted idocrase is on the order of 10 carats (for

brown material from in

Italy

8.50 (brown, Africa). 3.15, 2.95, 2.28 (Laurel,

bright

and

attractive as the grossular garnets,

The complexities

of

its

which

it

so

chemistry

lead to a huge range in properties and colors. Cuttable material

is

known from

Italy

(pale green, bright yellow), (green),

Kenya (brown and

Californite

is

(brown and green), Quebec

New York

(brown), Pakistan

green).

a massive idocrase-grossular mixture

from California and later found in various other localities, such as Africa and Pakistan. The density is 3.25-3.32 and there is a strong 4610 band in its spectrum, which is easily distinguished from the chrome spectrum of jadeite. reported

first

y=

1.504-1.507.

0.017-0.020.

Not diagnostic.

Spectral:

Luminescence:

None.

red clay.

Quebec).

Comments: Idocrase is one of the lesser known and more beautiful collector gems. When properly cut it is as strongly resembles.

Birefringence:

1.488-1.493;

Occurrence: Borate deposits in arid regions. Kern County, California: large crystals, often transparent. Inder borate deposit, Kazakhstan, USSR: as nodules in

green material.

NMC:

a = 1.486-1.489; ft = + ), 2 K= 37-52°.

and Africa), perhaps 15 carats

SI: 3.5 (brown, Italy); 7.1 (brown, Tanzania).

DG:

(

Stone Sizes: Gems over 50 carats or more could be cut from large transparent crystals.

Comments:

Inderite is very soft and difficult to cut, and only a few stones have been cut by hobbyists. There is plenty of cuttable material in existence, and although the material comes from only a few localities, it is not rarity. The surface of cut stones may become white and cloudy after cutting; care must be

considered a great taken

in

Name:

storage and to dry the stones after cutting. After the

INDICOLITE IOLITE

locality,

Inder Lake, Kazakhstan,

See Tourmaline.

See: Cordierite.

USSR.

J

JADE

See: Jadeite, Nephrite.

be seen

in rich,

deep green material, which has a Cr at 6915, weak at 6550 and 6300.

spectrum: strong line

JADEITE

(= JADE)

Luminescence: Pale colors may show dim white glow in LW. No reaction in SW. X-rays may give intense blueviolet glow in pale yellow and mauve stones.

NaAlSi 2 06.

Formula:

Monoclinic. Crystals very rare and

Crystallography: tiny,

Pyroxene Group.

usually granular with tough, interlocked crystals;

Colors:

Colorless, white,

Occurrence:

and pebbles.

fibrous; as alluvial boulders

all

Jadeite occurs chiefly in serpentine derived

from olivine rocks. Also as jade comes from Burma.

shades of green, yellow-

Hmaw-Sit-Sit,

green, yellowish brown, brown, red, orange, violet (mauve),

mixed with

gray, black.

Upper Burma: once thought

to be jadeite showing dark spots and green vein identified as ureyite (a different pyroxene

mineral) in natrolite.

USSR: apple green-colored United States

Orient

jadeite at

Imperial

Old Mine

River,

Canary New Mine

New

Moss-in-Snow Apple Green

Pea Green Flower Green

Density:

Oily

West Sayan.

mixed with nephrite.

colors; also

Comments:

Vitreous.

Jadeite

is

3.25-3.36; usually 3.34+.

None

(massive). Fracture splintery.

Very tough.

Pleochroism:

melanite

dom

0.012-0.020.

There

is

which

is

may have

a

often utilized in carving.

is

is

The

rich green material

sometimes called Yunan jade and light passes

through

it.

jewelry but

is

is

weak bands

at

value of a jade item

is

as

much

a function of the

workmanship and the antiquity

value as the color and quality of the jade

itself.

may

The make

jade a very specialized gemstone and the market largely

4500 and

diagnostic for jadeite but

is sel-

occasionally carved.

complexities of evaluation caused by these factors line

is

Chloro-

opaque, dark green to black jade that

in

artistry of the carving or

a strong line at 4375,

The 4375

is

seen

The

None.

identification.

4330.

known

extremely beautiful when

Jadeite has a distinctive spectrum useful in

Spectral:

best jade

from Burma

V= 67°.

Birefringence:

to weathering,

The

as well as lavender (mauve).

a = 1.640; p = 1.645; y = 1.652-1.667. Shadow edge usually 1.66. Optics:

Biaxial (+), 2

due

Yunan brown skin

usually marketed through

Burmese in origin and occurs in a wide range of colors. There are many simulants and imitations. Imperial jade is exceedingly rare and very costly. Another popular color is a fine apple green shade,

6.5-7.

Cleavage:

localities;

Zealand; Japan: Mexico: Guatemala: San Benito County, California: lenses and nodules in chert, various

Province, China. Green boulders

Hardness:

some

also fine translucent, Cr-rich jadeite at the Kantegir

Glassy Apple Green Spinach

Luster:

finest

albite,

pattern, later

Green Jadeite Color Terminology

The

alluvial boulders.

a collector market.

not

117

7

JASPER

78

Name:

Comments:

of the

jeremejevite was an exceedingly rare mineral available

Jade from the Spanish piedras de ijada. (stone is due to the healing powers for kidney ailments ascribed to jade, doubtless as a result of sympathetic magic because of the kidney or organ shapes of tumbled pebbles. Translated into French this was pierre del'ejade; a printer's error when the name first appeared in French made it pierre de le jade, which the English loins); this

people quickly chopped

See

down

to simply jade.

also: Nephrite.

The African

crystals are

After Pavel

V Jeremejev, Russian mineralogist

See: Quartz.

JET

See: Diopside.

Formula: C. Carbon, plus impurities; not a mineral.

JEREMEJEVITE Al 6 BsO, 5 (OH,F)

Formula:

1

.

tapering; also small grains.

Colors:

Colorless, pale blue-green, pale yellow-brown.

Luster:

Vitreous.

Hardness:

Colors:

Black, brownish.

Luster:

Dull; vitreous

Hardness:

coal seams as

when

polished.

2.4-4.

Density:

1.19-1.35.

3.28-3.31.

None. Conchoidal fracture.

Cleavage:

None; fracture conchoidal.

Cleavage:

Optics: e

(

in

black masses and lumps.

6.5-7.5.

Density:

Optics:

Amorphous. Usually

Crystallography:

Hexagonal; crystals elongated and

Crystallography:

—

=

1.637-1.644; o

=

1.644-1.653.

).

Cores of crystals sometimes biaxial (from USSR),

2V =

0-50°. Biaxial rims also

sometimes observed

in

Namibian material.

0.007-0.013.

Birefringence:

Light cornflower blue/colorless to light

Pleochroism:

yellow (Namibian material).

Vague absorption band

Luminescence:

at

No gems have been reported from the USSR material. However, the Swakopmund crystals have to

1

.66.

Other Tests: Burns like coal and gives burning coal odor with hot needle. Occurrence: Jet is fossilized wood, actually lignite, a form of brown coal. Henry Mountains. Utah; Colorado; New Mexico. Spain; Aude, France; Germany; USSR; Poland; India; Turkey.

size

None.

gems up

Blurred shadow edge on refractometer at

Stone Sizes: Carvings and cabochons of any desired could be cut.

about 5000.

Stone Sizes:

cut, with

Brittle.

Whitby, England; jet in seams; classic locality.

Occurrence: Cape Cross, near Swakopmund, Namibia: very long pyramidal crystals (up to 2 cm), blue-green color: e = 1.639; o = 1.648; birefringence 0.007. A few single crystals were found on Mt. Soktuj, Nerchinsk district. East Siberia, USSR, in loose granitic debris under the turf.

been

microscopic grains.

amazing in being both large and gemmy. Few gems have been cut from the material since the crystals are prized by collectors and the extent of the find is unknown. The crystals are not abundant at the locality, so jeremejevite will remain an extremely rare collector gemstone.

Name:

JEFFERSONITE

Spectral:

in

Namibian material was found,

and engineer.

JASPER

Uniaxial

only

Until the

about 5 carats possible. These

are a lovely blue-green color, are relatively easy to cut,

and are hard enough for wear. Typical faceted stone are from under 1 carat up to about 2 carats.

Jet has been known since Neolithic times and has been the most popular of all black gems. It has been used for many years in mourning jewelry. It is less popular and widely used in modern times. It takes a very good polish and is less brittle than the harder anthracite

Comments:

coal that

have a

it

flat

resembles. Jet

is

often faceted (the stones

bottom) to add sparkle to the somber tones of

jet jewelry.

Name: and

river

Originally from Gagates, the

(Gagae)

in

Asia Minor.

sizes

JULGOLDITE

See: Pumpellyite.

name

of a town

K

KAMMERERITE

exist,

(Mg,Cr) h (AlSb)0,o(OH) 8 (Chlorite Group).

Formula:

nonetheless, a testimony to the perseverence of

hobbyists!

.

Crystallography:

Triclinic; crystals

Name:

hexagonal shape,

bounded by steep sided pyramids. Colors:

Red

Luster:

Vitreous; pearly on cleavages.

Hardness: Density:

to purplish red, cranberry red.

KIMZEYITE

St.

See: Garnet.

KNORRINGITE

2-2.5. 2.64.

Perfect basal cleavage; micaceous; laminae

Cleavage

After A. Kammerer, the mining director at

Petersburg.

See: Garnet

KORITE

Also known as Ammolite; Calcentine.

Formula:

CaCOi.

flexible.

Optics:

a =

1.597;/*

=

1.598;

Crystallography:

1.599-1.600.

y

Biaxial; optic sign variable.

Birefringence:

Spectral:

(aragonite).

White, highly iridescent, especially shades of

Colors:

red and green.

0.003.

Luster:

Pleochroism:

Orthorhombic

Vitreous to resinous.

Strong; violet/hyacinth-red.

Hardness:

Not diagnostic.

None

Luminescence:

Density:

4.

2.80 (pure aragonite

=

2.95).

reported.

Cleavage:

Occurrence: In chromite deposits, associated with clinochlore and uvarovite.

Optics:

Several directions; brittle.

a =

1.520;

y=

1.670.

Erzincan, Turkey: distinct crystals.

Lake

Itkul,

Birefringence:

near Miask, USSR.

Occurrence: Korite is fossil ammonite shell, most notably from Alberta. Canada. The material is classified (class/genus/species) as Cephalopoda/ Ammonoidea/placenticeras meeki. These shells are approximately 71 million years old and vary in diameter up to approximately

California; Texas; Pennsylvania.

Stone Sizes: small.

Facetable material

Minute

is

quite rare and always

gems, 1-2 carats, have

been cut from

Turkish material.

Comments:

Kammererite

is

0.150.

a beautiful but rare min-

micaceous; consequently, it is extraordinarily difficult to facet, which has severely limited the availability of cut gems. It would have to be handled with great care to avoid cleaving. A few clean, well-cut gems do eral. It is

25 cm.

The

thick.

This

iridescent aragonite outer layer is

may be 6 mm

usually too thin to support itself in jewelry,

so korite (or ammolite)

is

often fabricated into triplets

with quartz tops and shale or synthetic spinel as backing material.

779

Only about 5% of the ammonites found

at the

KORNERUPINE

720

locality have any suitable gem material, and of these only about 20% of the shell can be used.

KORNERUPINE 2

Orthorhombic;

Crystallography:

brown and reddish pebbles, in gravels. Mogok, Burma: greenish-brown material in gem gravels. Kwale district, Kenya: light green material, some large clean pieces; colored green by vanadium.

Mg,AUSi,Al,B)s0 ,(OH).

Formula:

carats have been reported. Also from Matale, yellow-

Tanzania:

crystals prismatic; also

chrome

variety with green color, cuttable.

Gatineau County, Quebec, Canada: large

gemmy

Itrongahy, Madagascar: large

Colorless, white, pink, greenish yellow, blue-

Colors:

tals,

green, sea green, dark green, brown, black.

Hardness:

Most gems are under

Stone Sizes:

6-7.

sional large material

Perfect 2 directions; fracture conchoidal;

Cleavage:

dark

dark green crys-

also pale aquamarine-blue.

Betroka and Inanakafy, Madagascar: gray to brown matic crystals.

Vitreous.

Luster:

crystals,

green to greenish yellow.

fibrous, columnar.

gem

Africa yields a

from

in

pris-

5 carats, but occa-

Lanka, Burma, or East the 25-30 carat range. Canadian Sri

brittle.

crystals are large (up to 2 inches across) but are not

Density:

3.27-3.45;

gems

The largest crystals of all, from Greenland, yield only small cut stones. SI: 21.6 (brown, Sri Lanka); 10.8 (brown, Madagascar);

generally cuttable.

are 3.28-3.35.

varies with locality:

Optics:

8.1 (green, Sri

a

Locality

r

P

Density

Birefrin-

gence Madagascar Lanka

Sri

catseye

Germany Natal

Greenland East Africa

1.661

1.673

1.669 1.673 1.675 1.682 1.667 1.662

1.681

1.686 1.687 1.696 1.679 1.675

1.674 1.682 1.690 1.687 1.699 1.682 1.677

DG: PC:

0.013 0.013 0.017 0.014

3.28 3.35

— 3.37 3.45 3.30

0017 0.015 0.015

—

Lanka).

6.4 (Sri Lanka).

16.50 (golden, Sri Lanka); 7.57 (catseye, Sri Lanka).

Comments:

Star kornerupine also has been found (Mogok, Burma) but is very rare. Kornerupine is generally dark brown or green and not very attractive due to the somber colors. The light green material from Kenya is much more appealing, but the sizes are always small

(under 3 carats as a

rule).

The color is caused by traces of many stones are in

Fe, Cr, and V. Despite the fact that Biaxial (— ),

2V= 3-48°; gems sometimes pseudo-uniaxial.

Dispersion:

rare

gemstone and,

when

0.018.

Pronounced and

Pleochroism:

museums and private collections, kornerupine

visible to the

naked eye:

for the collector,

is

a rather

worth acquiring

available.

Name:

After the Danish geologist Kornerup.

Sri Lanka; Madagascar: yellowish brown/brown/greenish.

Kwale

District,

Kenya: intense green/light green/greenish

KUNZITE

Spodumene.

See:

yellow.

Kenya; Tanzania: emerald green/bluish gray/reddish

KURNAKOVITE

purple.

Formula:

Mg

2

Dimorph

B60u

of Inderite.

15H 0. 2

Greenland: dark green/reddish blue/light blue. Crystallography:

Weak band

Spectral: Inclusions:

seen at 5030.

Zircon, apatite crystals.

Luminescence:

None

(

Sri

Triclinic. Crystals large

and blocky,

often in clusters; large cleavable masses; aggregates.

Lanka or yellowish Burmese in LW and (

)

Colors:

Colorless, with a white surface coating.

Luster:

2.5-3.

green gems, stronger in East African stones)

Density:

SW. Occurrence: tals (not

First

gemmy),

found

in

Greenland

in radiating crys-

later in cuttable fragments.

Finskenaesset, Southwest Greenland: giant crystals up

cm, yielding cabochons and small (up to ~ 2 carats) gems of dark green color. Weligama gem gravels, Matara district. Sri Lanka: green-

Cleavage: Optics:

1.78-1.85.

Good a=

Biaxial (+), 2

1

direction. Fracture conchoidal. Brittle.

1.488-1.491;/}

=

V= 80°.

to 23

faceted

dark yellowish-green catseyes. The eye effect is intense. Stones tend to be small, but cabochons over 7

Birefringence:

Pleochroism:

0.027-0.036.

None.

ish to

Spectral:

Not diagnostic.

1.508-1.511;

y=

1.515-1.525.

KYANITE

Luminescence:

None.

0.020.

Pronounced: violet-blue/colorless/cobalt-

Pleochroism:

Also pleochroic

California material could yield stones of

hundred carats from large transparent masses or

several

Dispersion:

blue.

across and large masses.

Stone Sizes:

0.017 (Cr-kyanite up to 0.033).

Birefringence:

Occurrence: Borate deposits in arid areas. Inder Lake, Kazakhstan, USSR. Boron, Kern County, California: crystals to 24 inches

121

in all

shades of yellow-green and green.

One line observed in deep red at 7100 and deep blue, with dark edge at about 6000.

Spectral: lines in

2

cleavages.

Comments:

Kurnakovite

is

similar to inderite. Both

are colorless and very uninteresting as faceted gems,

which

why

is

obtainable

very few have been cut.

in large size,

The

material

but softness and cleavage

is

make

After N.

S.

Occurrence:

Many

Kurnakov, Russian mineralogist and

chemist.

to 2 inches long,

India;

KYANITE

Trimorphous with Andalusite,

Sillimanite.

Formula:

AhSiOs.

Crystallography:

Brazil: large blue

low, pink, nearly black.

Color zoned

in individual crystals.

Vitreous; pearly on cleavage.

some

4-7.5; varies with direction in single crystals.

Perfect

facetable. Virginia: Georgia; Massachusetts.

blue, with

Cr and

Ti.

and blue-green crystals. Kenya: large blue crystals, banded

Switzerland: with staurolite in schist.

1

Density:

3.53-3.68;

they are seldom completely clean over 5 carats, however.

Many

Cr-kyanite

=

of these stones are Brazilian;

6.57 (blue-green, North Carolina).

gems

ROM:

a = 1.710-1.718; = 1.721-1.723; y =1.727-1.734. = 1.724; y = 1.731; birefrinCr-kyanite: a = 1.714; gence = 0.017; S.G. - 3.67. a = 1.720; /3 = 1.730; y = 1.753; birefringence = 0.033; S.G. = 3.70.

Optics:

(~),2V = 82-83°.

are African.

Tanzania).

DG:

3.67-3.70.

some

SI: 10.7 (blue, Brazil); 9.1 (green, Brazil); 4.9 (blue,

direction.

usually upper end of range.

color, facetable.

Gems have been cut up to about 20 carats;

Stone Sizes:

PC: Cleavage:

Yancy

District,

Kenya: fine blue

Blue, blue-green, green; also white, gray, yel-

Hardness:

especially

States,

with green; also colorless!

Triclinic. Crystals bladed, flattened

and elongated; fibrous, massive. Colors:

United

Italy.

Machakos

Biaxial

in the

County, North Carolina: deep blue or green crystals, up

Mozambique: dark

See: Dolomite.

and granite pegmatites.

known.

Vermont: Connecticut:

KUTNAHORITE

Luster:

In schists, gneiss,

localities are

Various places

cutting a real chore.

Name:

Variable fluorescence, mostly dim red

Luminescence: in LW.

14.0 (blue, Africa); 8.55 (bluish, Africa).

40.26, 12.38 (rectangular step-cut, Brazil).

Kyanite is very rare as a faceted gem, espefrom inclusions and flaws. The material is extremely difficult to cut because of its perfect cleavage and the extreme variability in hardness in different direc-

Comments: cially

if

free

tions in the

same

known

to exist.

Name:

From

the

crystal.

A

few catseye kyanites are

Greek kyanos. meaning

blue.

LABRADORITE

LAWSONITE

See: Feldspar.

CaAl

Formula:

LANDERITE

2

Si 2 07(OH) 2

H

2

0.

See: Garnet

Orthorhombic. Crystals prismatic; mas-

Crystallography: sive, granular.

LANGBEINITE K Mg (S0

Formula:

2

2

Crystallography:

6+. 3.05-3.12.

Cleavage:

Vitreous.

Hardness:

Biaxial

3.5-4.

(+),2V=

Pleochroism:

Faint greenish white in

LW

ish

carats.

Not diagnostic.

Occurrence:

feet thick.

amorphic

None.

Low-temperature metamorphic rocks; met-

schists;

glaucophane

Santa Clara, Cuba;

Colorless stones potentially up to 10-15

Cabochons of any

1.684-1.686.

(New Luminescence:

Stone Sizes:

y =

Blue/yellow-green/colorless or pale brown-

Occurrence: Evaporite deposits from marine waters. Saskatchewan, Canada; North Germany; Austria; India. beds up to 7

1.674-1.675;

yellow/deep blue-green/yellowish.

Spectral:

New Mexico:

=

0.019.

Mexico).

Carlsbad,

j}

84°.

High.

Dispersion:

Brittle.

N= 1.536.

Luminescence:

1.665;

Birefringence:

None. Fracture conchoidal.

Cleavage:

Perfect in 2 directions.

a =

Optics:

2.83.

Optics:

Vitreous to greasy.

Density:

ish, violet.

Density:

Luster:

Hardness:

Colorless, white, gray, yellowish, greenish, pink-

Luster:

Colorless, white, gray, blue, pinkish.

Isometric. Crystals are rare; usually

massive, bedded; in nodules. Colors:

Colors: 4 ),.

Italy;

size.

Italy;

Japan;

schists.

New

Caledonia; France-

other locations.

Tiburon Peninsula, California: original material.

Comments:

This material

is

nondescript and

is

cut

Covelo,

The gems are soft, pale colored, or no fire. Few cut stones have been reported,

Mendocino County,

California: 2-inch crystals.

solely as a curiosity. colorless, with

Stone Sizes:

The maximum

likely is 2-3 carats.

Gems are

pale blue in color.

but this may be due to a lack of interest rather than a lack of suitable rough.

Comments:

Name:

stone, seldom reported and generally unavailable.

After A. Langbein of Leopoldshall, Austria.

Name:

LAPIS LAZULI

See: Lazurite.

is

extremely rare as a faceted

After Professor A. C. Lawson of the University

of California.

722

Lawsonite

LAZURITE LAZULITE

Series to Scorzalite: (Fe,Mg)Al 2 (P0 4 ) 2 (OH) 2

(Mg,Fe)Al 2 (P04) 2 (OH) 2

Formula:

.

.

Monoclinic; crystals acute pyramidal;

Crystallography:

massive, compact, granular.

Colors:

Blue, blue-green, light blue, deep azure blue.

Luster:

Vitreous to dull.

123

from massive lazulite, such as the material from New Hampshire and California. Both color and pleochroism are the same for lazulite and scorzalite, but the optical properties and density are quite different, varying with the Fe/Mg ratio, and therefore are useful in distinguishing the two species.

Name:

Lazulite

is

from the German

ing blue stone. Scorzalite

is

named

lazurstein,

after E.

P.

mean-

Scorza, a

mineralogist at the Brazilian Department of Mines.

Hardness:

5.5-6.

Cleavage:

Indistinct to good,

1

direction; fracture un-

even; brittle.

LAZURAPATITE

LAZURITE

(=

See: Apatite.

LAPIS LAZULI)

Sodalite Group.

Table of Properties in Lazulaite-Scorzalite Series

Formula: Property

Lazulite

[MgJ

Mg

V}

Fe

Vl

Scorzalite [FeJ

Crystallography:

3.22

3.38

1.604-1.625 1.633-1.653 1.642-1.662

1.626 1.654 1.663

1.627-1.639 1.655-1.670 1.664-1.680

c-)

C-)

c-o

0.037

62° 0.038-0.040

compact, disseminated,

Optics:

a P Y Sign

—

69° 0.031-0.036

2V Birefringence

Deep

Colors:

Streak:

Light blue.

Luster:

Dull.

Density:

gem

None.

Not diagnostic.

5-6 (depending on impurity content).

known, as follows. Palermo Quarry, North Groton, New Hampshire; Graves localities are better

Mountain, Georgia; South Dakota. Angola; Horrsjoberg, Sweden; Madagascar. Yukon, Alaska: fine gemmy crystals. Champion Mine, Mono County, California: masses to 6

Potosi, Bolivia; Lobito Bay,

inches across. district,

1.635/1.645; S.G.

Minas Gerais, 1.604-1.629;

fi

India:

=

gemmy

0.031-0.037; S.G.

Stone Sizes:

y =

gemmy

crystals;

a =

1.638-1.666; birefrin-

3.07-3.24.

Faceted gems are usually

in the 0.5-2 carat

Even the small gems tend to be badly flawed. The large masses from California are not clean enough to facet. Lazulite

makes a magnificent, deep blue

gemstone. The supply of rough is limited, although the mineral itself has widespread occurrence. Faceted lazulite

strongly resembles blue apatite.

marginal for use

Optics:

in jewelry.

pyrite present.

Imperfect; none in massive material. Frac-

Isotropic. TV

Inclusions:

-

1.50.

Pyrite (brassy yellow)

and white

calcite in

massive material.

Luminescence: Orange spots or streaks in LW( Afghanistan and Chile), dimmer and more pink in SW. X-rays cause yellowish glow in streaks. May fluoresce whitish in SW.

Chemical Test:

A drop of HC1 on lapis releases H

2

S gas

The hardness

is

Cabochons have been cut

Contact metamorphic mineral

in lime-

stone, formed by recrystallization of impurities; also in granites. Italy:

range, with clean stones over 5 carats extremely rare.

Comments:

much

ture uneven.

Occurrence:

=

if

crystals (indices 1.615/

3.17).

1.628-1.655;

or higher

(rotten egg odor).

Brazil: fine blue

=

Pure: 2.38-2.45.

lapis: 2.7-2.9

Cleavage:

Occurrence: Quartz veins; granite pegmatites; metamorphic rocks, especially quartzites. Scorzalite is a relatively rare mineral; lazulite is more abundant, and the

Bhandara

blue, azure blue, violet-blue, greenish

Strong: colorless/blue/dark blue.

Luminescence: Spectral:

in veins.

blue.

Hardness: Pleochroism:

gence =

Isometric. Crystals very rare, dode-

cahedral, up to about 2 inches in size. Also massive,

3.08

Density

(Na,Ca) 8 (Al,Si), 2 024(S,S04).

Labrador; Mogok, Burma; Pakistan.

California: blue-gray with white spots.

Colorado: stringers

in

limestone, dark color,

much pyrite,

Mountain

from Italian in the western part of the state. Badakshan, Afghanistan: among the oldest operating mines in the world (7,000 years). Lapis occurs in large blocks and crystals in white matrix. Source of the world's finest lapis.

Sludyanka River, Mongolia: light blue lapis, with pyrite. Chilean Andes: gray and blue mixture, color inferior to Afghan material.

LEGRANDITE

124

Rough blocks from Afghanistan, of fine known up to 100 kg. One block of Chilean found in a Peruvian grave, was 24 X 12 X 8

Stone Sizes:

1

color, are

mens

material, inches. Pitti

A 40.5 cm

vase of fine blue material

tall

Palace, Florence,

is in

the

Italy.

The gem known as lapis lazuli, or simply composed of lazurite, haiiyne, sodalite, and nosean, all members of the sodalite group of minerals. Lazurite itself may be considered a sulfurComments: lapis,

actually a rock,

is

rich haiiyne. Calcite

and

pyrite in various percentages

The finest lapis is considered

are also present in the rock. to be a solid,

deep blue with no white

calcite spots

just a sprinkling of brassy yellow pyrite.

found only

in

Afghanistan and Pakistan,

interesting quantities.

The Colorado

very well suited to

is

material

is

source

in the

Many

mineral speci-

locality.

Comments: This mineral was first described in 1932, and it has become a very popular specimen mineral with collectors because of crystal groupings.

color

is

too soft for wear, but the yellow

unique among gems and very distinctive. This

one of the

Name:

who

intense yellow color and esthetic

its

It is

loveliest of all the rare collector

is

gemstones.

After a Belgian mine manager, Mr. Legrand,

collected the

is

LEPIDOLITE

first

Mica

quite

Formula:

specimens. family.

K(Li,Al)j(Si,Al)4O 10 (F,OH)2.

Monoclinic. Crystals tabular; also mas-

Crystallography:

mens jewelry because

a rich blue color and does not

are very hard to find.

but transparent crystals are extremely rare

commercially

fine but of limited availability.

Lapis

even

gems

exist,

and

Such material in

carat

it

has

show wear easily. It is fairly is dark enough not

ses of plates, spheroidal masses.

Colorless: Yellow, pink, purplish, white, grayish.

tough, takes an excellent polish, and to

be a problem

Name:

From

in

color coordination with clothes.

a Persian word, lazhward,

meaning

blue.

Luster:

Pearly on cleavage.

Hardness: Density:

LEGRANDITE

2.8-3.3.

Perfect and easy

Cleavage:

Zn (OH)As0 4 H 0.

Formula:

2.5-4.

2

2

Optics:

Monoclinic. Crystals prismatic, also

Crystallography: in sprays

and

Colors:

Yellow, colorless.

Luster:

Vitreous.

a=

Biaxial (-), 2

1.525-1.548;

Biaxial

(

=

1.554-1.587.

0.018-0.038.

Spectral:

1.675-1.702;

+ ),2V=

Absorption stronger

Pleochroism:

in the

plane of the

Not diagnostic.

Luminescence:

/}

=

1.690-1.709;

y=

None.

Almost exclusively

Occurrence:

Poor. Fracture uneven. Brittle.

a

Optics:

y=

cleavage.

3.98-4.04.

Cleavage:

1.551-1.585;

fans.

4.5.

Density:

=

direction.

V = 0-58°.

Birefringence:

Hardness:

/3

1

in granite

pegmatites;

also in tin veins. 1.735-1.740.

50°.

San Diego County, California: Gunnison, Colorado; Black South Dakota: Wyoming; Arizona; New Mexico; New England, especially Maine. Sweden; Germany; Finland; Czechoslovakia; USSR; Madagascar; Japan; Bikita, Zimbabwe. Brazil: fine pink and reddish crystals. Hills,

Birefringence:

Pleochroism: Spectral:

0.060.

Colorless to yellow.

Not diagnostic.

Luminescence:

None.

Occurrence: In vugs in limonite. Only occurrence is in Mexico. Florde Pena Mine, Nuevo Leon, Mexico: first discovered

Large nodules from California are up to 6

Stone Sizes:

inches or more across. Lepidolite, like the other micas, rarely transparent

enough

difficult to cut that

to facet,

and then

it

few people ever attempt the

is

is

so

feat!

Facetable lepidolite does exist, notably from Brazil.

locality.

Ojuela Mine, Mapimi, Mexico: best-known locality, from which come magnificent crystal clusters, single crystals up to 6 cm long and 7.5 mm thick. This is the source of

Comments:

the only cuttable material.

nonexistent because of the perfection of the cleavage

Stone Sizes: The maximum to expect in a cut legrandite is about 2-4 carats, although a 10-carat stone has been reported!

A larger stone would be a great rarity, and even

Reddish granular or massive lepidolite

is

usually slabbed for ornamental purposes, such as ashtrays,

paperweights, and bookends. Faceted micas are virtually

and the variable hardness within

Name:

From

the

Greek

crystals.

lepis, (scale)

scaly nature of the massive material.

because of the

LUDLAMITE LESSERITE

See: Inderite.

a=

Optics: Biaxial

LEUCITE

1.809;

Birefringence:

0.050.

Pleochroism:

Pale

Spectral:

Colors:

Colorless, white, gray, yellowish.

Luminescence:

Luster:

Vitreous; dull on

Hardness:

some

5.5-6.

Poor. Fracture conchoidal. Brittle.

Cleavage: Optics:

Isotropic; TV - 1.50.

Optically

(

+

)

uniaxial.

if

to zero.

Grand

Luminescence: Medium-bright orange none. Bluish glow in X-rays. Occurrence:

LW (Italy) or

in

Reef, Arizona: large crystals,

In potassium-rich basic lavas.

Australia.

transparent leucite crystals. These are colorless, up to

cm.

Faceted gems over 1 carat are very rare. V2 carat is remarkably large for linarite. Crystals tend to be filled with fractures or are translucent and are usually very thin blades on rock. Grand Reef material has yielded cut gems in the 2-carat range.

and

it

is

been cut to about 3

in

Comments:

Name:

is

extremely rare

is

abundant

in

various lava rocks

in facetable crystals.

The

is

material

Formula:

From

Greek

the

LIDDICOATITE

its

leukos,

meaning

a lovely collector item and an extremely

After the locality, Linares, Spain.

Name:

appeal except for

been

rare one.

LIZARDITE

little

magnificent,

cutting due to the softness and cleavage of

extreme scarcity. Stones often have a slight milky or cloudy look, and anything over 3 carats is likely to be included. has

is

the mineral further complicates the salvaging of a large

gem. This

Leucite

blue color of linarite

found. Clean areas of crystals are usually very small, and

There is very little of this material, always small, and clean only in very tiny stones.

carats.

but

The

a pity that large facetable rough has not

breakage Italian material has

cuttable.

Stone Sizes:

Comments: near Rome, Italy: source of the world's only

Stone Sizes:

some

Anything over

Wyoming; Montana: Arkansas; New Jersey. British Columbia; France; Germany; Zaire; Uganda; Hills,

None.

color.

Low

Birefringence:

blue.

Occurrence: Secondary mineral in the oxidized zones of lead-copper deposits. Blanchard Mine, Socorro County, New Mexico; California; Montana; Utah: Idaho; Nevada. England; Scotland: Spain; Germany; Sardinia; USSR; Canada; Argentina; Peru; Chile; Japan; Australia: Tsumeb. Namibia. Mammoth Mine, Tiger, Arizona: large crystals of fine

crystals.

2.47-2.50.

Density:

blue/medium blue/Prussian

Not diagnostic.

trapezohedral; granular.

1

1.859.

Tetragonal (pseudo-cubic). Crystals

Crystallography:

about

y=

),2K=80°.

(

KAlSi 2 06.

Formula:

Alban

1.838,

/J

125

white.

See: Tourmaline.

See: Serpentine.

LUDLAMITE 4H

Fe 3 (P04b

2

0.

Monoclinic. Crystals tabular, wedge-

Crystallography:

shaped; also granular.

LINARITE

Crystallography: in

Apple green, dark green, pale green, greenish

Colors:

PbCu(S0 4 )(OH)

Formula:

2

.

Monoclinic. Crystals prismatic; also

white, colorless.

Streak:

Pale greenish white.

Luster:

Vitreous.

druses and crusts.

Colors:

Dark azure

Streak:

Pale blue.

Luster:

Vitreous to subadamantine.

blue.

Hardness: Density:

Hardness: Density:

Cleavage:

Brittle.

Optics:

5.30.

Perfect

3.19.

Perfect

1

direction. Fracture conchoidal.

Brittle.

2.5.

Biaxial

Cleavage:

3.5.

1

direction. Fracture conchoidal.

a = .650-1.653; /3 = (+),2V= 82°. 1

Birefringence:

1.667-1.675;

0.038-0.044.

y=

1.688-1.697.

726

LUSAKITE

Spectral:

Not diagnostic.

Luminescence: Occurrence:

Stone Sizes: Ludlamite is seldom cut, and transparent material is always small. The potential may exist for 5-10

None.

carat gems, but most are in the 1-2 carat or smaller

A secondary mineral

of ore deposits; also

due

in

the oxidized zone

to the alteration of primary

phosphates in granite pegmatites. New Hampshire. Cornwall, England; Hagendorf, Germany. Blackbird Mine. Lemhi County. Idaho: fine crystals up to V2 inch across.

South Dakota: crystalline masses ter with 7

to 12 inches in

mm crystals at Keystone.

range.

Comments:

Ludlamite has a lovely green color but is known from only a few localities, and cut stones are extremely rare. too soft for wear. Large crystals are

Name:

After Henry Ludlam, of London, English min-

eralogist

and

collector.

diame-

LUSAKITE

See: Staurolite.

M MAGNESIOCHROMITE

See: Chromite.

is

obvious even

in

small stones, and larger

gems have

a

sleepy look, or fuzziness, due to the doubling of back

MAGNESITE

facets as seen through the table. Faceted magnesite

MgCOj.

Formula:

and the material

rarely seen,

Facetable crystals

Hexagonal (R). Crystals very rare (rhombs); massive, compact, fibrous.

Crystallography:

Name:

Colorless, white, gray, yellowish to brown.

MAJORITE

Luster:

Vitreous to dull.

MALACHITE

Density:

3.5-4.5.

only from Brazil.

See: Garnet.

CuCOj(OH)

Formula:

2.

3.0-3.12.

Crystallography: Perfect rhombohedral; brittle.

Cleavage: Optics:

is

relatively difficult to cut.

In allusion to the composition.

Colors:

Hardness:

come

is

o

=

1.700-1.717; e

=

Monoclinic. Crystals are prismatic,

usually small; also massive,

sometimes banded;

stalactitic;

as crusts.

1.509-1.515.

Green (various shades due

Colors:

Uniaxial (— ).

to

admixed clay

in

massive material), dark green. Birefringence:

0.022.

Luminescence: Blue, green, white greenish phosphorescence. Other

Tests:

Effervesces in

warm

in

SW, often with

Streak:

Pale green.

Luster:

Adamantine

Hardness:

acids.

Occurrence: Alteration product of magnesium-rich rocks; sedimentary deposits; as a gangue mineral in hydrothermal ore deposits. Norway; Austria; India; Algeria; Korea; Zaire; South

Density:

3.5-4.5.

4.05 (as low as 3.6 in admixtures or

Cleavage:

Perfect

a=

Optics:

Brumado, Bahia, Brazil: magnificent and large rhombshaped crystals, often transparent, colorless.

Biaxial (-), 2

Largest

known

cut magnesite

carats (Sit from Brazil material.

under 10-15

Comments: site

is

Mean

1.655;

direction. Fracture uneven. Brittle. ft

=

1.875;

y=

1.909.

V= 43°.

index reading of 1.85 on massive material.

Birefringence:

134.5

Most other gems are

1

0.254.

Pleochroism:

Colorless/yellow-green/deep green.

carats.

Gems

of completely transparent

are both rare and beautiful.

The huge

when

fibrous.).

Africa.

Stone Sizes:

in crystals; vitreous; fibrous; dull.

Luminescence:

magne-

Other

birefringence

727

Tests:

None.

Effervesces

in

warm

acids.

128

MANGANOCOLUMBITE

Occurrence:

In the oxidized portions of

copper ore

bodies, with azurite and cuprite.

Arizona, at Bisbee and Gila, other localities;

New Mexico;

Utah: Tennessee.

Zambia; Broken Hill, N.S. W., Australia. Tsumeb, Namibia: magnificent large crystals. Mednorudyansk, USSR: immense masses, some up to 50 tons! Much good for cutting. Also mine at Nizhne-Tagilsk. Zaire: banded material, also stalactitic, most familiar on marketplace.

Stone Sizes: Cabochons and carvings can be virtually any size from banded material. Stalactites have been found several feet long. In the USSR place settings, including dinner plates and goblets, have been carved from fine malachite. Exquisite inlay work has also been done, and malachite slabs have been used as paneling in palace rooms. Facetable crystals are virtually nonexistent. Any cut gem would be very small, less than 2 carats.

Comments:

Malachite

is

one of the most popular and

beautiful of decorative stones. Its rich, patterned coloration in shades of green is unique among gems. Malachite can (with great care be turned on a lathe to make goblets and candlesticks. It is extensively used to make cabochons, beads, boxes, and carvings of all kinds. Fibrous aggregates are packed masses of crystals, and these also take a high polish. Facetable crystals are microscopic in size since larger ones are too opaque to let light through. A faceted gem larger than V2 carat would be opaque. )

Name:

From

a

Pleochroism: Shades of brown and red-brown. Also deep red/pale pink.

Luminescence:

None.

Not diagnostic.

Spectral:

Occurrence:

In granite pegmatites;

Minas

Cuttable crystals seldom reach 1 inch in and gems over 10 carats are rarities. However, the material is so dense that even a small stone is relatively

Stone Sizes:

heavy.

DG:

3.05 (red-brown, Brazil).

Comments: Manganotantalite makes a spectacular redbrown gem that is a very rare collector's item. Transparent material is light enough in color to allow lots of light to enter and leave a cut gem, and properly cut stones are lively and brilliant. Cutting

See: Manganotantalite.

Series to

Manganocolumbite;

Ferrotantalite; Columbotantalite.

(Mn,Fe)(Ta,Nb) 2

Name:

MANGANPECTOLITE

6

:

MARCASITE

Dimorph

ular,

Streak:

Dark

Luster:

Vitreous to resinous.

red.

red.

Orthorhombic. Crystals abundant,

Mozambique Distinct

1

material

=

7.73-7.97.

direction. Fracture subconchoidal

to uneven. Brittle. 2.19;

=

2V large. 0.150.

2.25;

y =

2.34.

Pale brassy yellow to whitish;

Streak:

Greenish black.

Luster:

Metallic; opaque.

Density:

Cleavage:

High.

may be

iridescent.

6-6.5.

4.85-4.92.

Distinct

1

direction. Fracture uneven. Brittle.

Marcasite forms at low temperatures, espe-

sedimentary environments such as clays, shale, coal beds, and in low temperature veins. Marcasite is abundant and widespread throughout the world. cially in

Oklahoma; Missouri; Kansas; Wisconsin. Germany; Austria; Bolivia; France; Czechoslovakia.

Illinois;

Dispersion:

cockscomb-shaped aggregates.

Colors:

Occurrence: /}

tab-

pyramidal, often with curved faces; also massive;

Hardness:

5.5-6.5.

of Pyrite.

FeS2.

Crystallography:

Orthorhombic. Crystals short prismatic;

Brownish black, reddish brown, scarlet

Birefringence:

See: Pectolite.

See: Calcite.

3:1.

Colors:

Biaxial (+),

because of

See: Scorodite.

granular; radial; globular;

a =

difficult

After the composition, a manganiferous tantalite.

Formula:

Mn: Fe =

massive.

Optics:

is

the cleavage.

Greek word meaning mallow (an herb

MANGANOTANTALITE

Cleavage:

quality crystals. Also

size,

MARBLE

Density:

gem

from the Morrua Mine, Zambesia.

MANGANOCOLUMBITE

Hardness:

placer

Gerais, Brazil: facetable crystals.

Alta Ligonha, Mozambique:

MANSFIELDITE

Crystallography:

in

Pala, California; Portland, Connecticut'; Amelia, Virginia. Andilana, Madagascar; Sanarka River, Urals, USSR; Sweden; Wodgina, Western Australia.

plant), in allusion to the color.

Formula:

sometimes

deposits.

MELLITE England:

the chalk deposits along the coast and at

in

129

Crystal clusters have been found up to

Stone Sizes:

Folkstone.

several inches long. Clean, facetable material

Stone Sizes:

however; the material cabochons.

Massive material exists that could cut cabsize. Marcasite is often faceted,

ochons of any desired the stones having

flat

backs. This type of jewelry was

The cutting style is Such gems were set in

very popular in the Victorian era.

known

as the flattened rose-cut.

white-metal settings such as rhodium-plated

Comments: and

it

was

silver.

rare,

is

very

sometimes cut into small

Comments:

Meliphanite is an extremely rare gemstone, and perhaps fewer than 5-10 faceted stones have ever been cut.

Name:

Marcasite was used by the ancient Greeks,

is

From Greek words meaning appearing as honey.

in allusion to the color.

also polished in large slabs by the Incas of

Central America. There were surges of popularity for

MELLITE

marcasite jewelry in the eighteenth century and the

seldom seen in modern and a sharp blow can easily

Victorian era, but marcasite jewelry.

quite brittle,

It is

crack a stone and loosen "marcasite"

it

is

in its setting.

antique jewelry

in

is

actually the

marcasite, pyrite (see page 154). Steel imitation marcasite but is

is

Much

is

of the

Al 2 G,(COO)6

Formula:

Crystallography:

18H 2

'

(aluminum

mellitate).

Tetragonal. Crystals prismatic, pyrami-

dal; granular, nodular, massive.

dimorph of

also used as an

magnetic, whereas marcasite

Colors:

Honey

Streak:

White.

Luster:

Resinous to vitreous.

yellow, reddish, brownish, rarely white.

not.

Name:

common

Of Arabic or Moorish

origin;

it

was applied

to

crystallized pyrite by miners until about 1800.

MARIALITE

Hardness: Density:

See: Scapolite.

1.58-1.64.

Cleavage:

MEIONITE

2-2.5.

Indistinct. Fracture conchoidal. Sectile.

See: Scapolite.

Optics:

MELANITE

o

=

1.539-1.541; e

See: Garnet.

Sometimes anomalously

MELINOPHANE

See: Meliphanite.

MELIPHANITE

MELINOPHANE)

Formula:

(=

Birefringence:

Pleochroism:

(Ca,Na) 2 Be(Si,Al) 2 (0,OH,F)7.

Spectral:

Tetragonal. Crystals thin and tabular;

Crystallography:

=

1.509-1.511.

Uniaxial (— ).

also aggregates.

Colors:

Colorless, shades of yellow, reddish.

Luster:

Vitreous.

biaxial.

0.028-0.032.

Weak; yellow/yellow-brown.

Not diagnostic.

Dull white in SW, or medium light blue. Medium light blue in LW (Germany) or lemon yellow. May be weak brown in SW (USSR).

Luminescence:

Occurrence:

A

secondary mineral

in

brown coals and

lignites.

Hardness: Density:

Cleavage: Optics:

5-5.5.

Artern and Bitterfeld. Germany; Paris Basin, France; Czechoslovakia; Tula. USSR.

3.0-3.03.

Perfect

o=

1.612;

1

direction. Fracture uneven. Brittle.

e=

1.593.

Comments: Mellite is one of the most unusual of all gems, being an organic material formed by inorganic

Uniaxial (— ). Birefringence:

Pleochroism:

Stone Sizes: Mellites are always small (1-3 carats) and may be quite transparent.

0.019.

Distinct in shades of yellow

processes, just the reverse of the situation with pearls

and

red.

and

coral. Crystals are additionally unusual in being

pyroelectric (they generate an electric current Spectral:

Not diagnostic.

Luminescence:

None.

heated). Mellite beautiful

when

is

cut.

and very fragile, but Truly this is one of the most soft

is

when quite

interest-

ing of the rare gemstones.

Occurrence:

Nepheline syenites and skarns. Julienhaab district. Greenland; Langesundsfjord. Norway;

Name:

Gugiya, China.

allusion to the color.

From

the Latin

word

mel.

meaning honey,

in

MESOLITE

130

MESOLITE

Hexagonal. Crystals prismatic and tab-

Crystallography:

See: Natrolite.

ular; in grains.

MICA

See: Lepidolite.

MICROCLINE

See: Feldspar.

MICROLITE

and masses. Pale yellow to brown, reddish, green.

Streak:

Pale yellow to brown.

Luster:

Vitreous to resinous.

2.46-2.61.

None. Fracture conchoidal to uneven.

Cleavage:

=

o

1.532-1.551; e

=

Brittle.

1.529-1.548.

Uniaxial (— ). Birefringence:

0.003.

Not diagnostic.

Spectral:

None.

5-5.5.

Occurrence: In vugs thermal veins.

4.3-5.7; usually 5.5.

Octahedral (not always evident). Fracture subconchoidal to uneven. Brittle. Cleavage:

N = 1.93-1.94

Metamictization Spectral:

5.5-6.

Luminescence:

Hardness:

Optics:

Vitreous.

Optics:

Colors:

Density:

Luster:

Density:

(0,OH,F).

Isometric. Crystals octahedral; also

Crystallography: grains

6

Colorless, pale green, yellowish, yellowish green.

Hardness:

Pyrochlore Group.

(Na,Ca) 2 Ta 2

Formula:

Colors:

if

slightly

metamict; also 1.98-2.02.

may cause anomalous

birefringence.

Luminescence: Occurrence:

and

syenites; hydro-

Gotthard, Switzerland: green crystals. Guanajuato, Mexico: yellow and yellow green crystals

St.

on matrix,

flat, platelike.

Africa: occasional small facetable crystals found. Crystals occur up to about 4

Stone Sizes:

Not diagnostic.

in granites

cm

across,

but facetable areas in such crystals are very small. Stones

None.

over

Primary mineral

in granite

pegmatites.

1

carat could be considered large for the species.

Comments:

Milarite

was

originally

known

as a green

Connecticut; Maine; Massachusetts; South Dakota; Col-

mineral, until fine yellow crystals were discovered in

New Hampshire. Greenland; Norway; Sweden: Finland; France; Madagascar; Western Australia. Amelia. Virginia (Rutherford Mines): green and brown

Mexico

orado;

some gemmy ones up to a few inches fine green crystals, some gemmy.

crystals,

Brazil:

Cabochons can be cut

Stone Sizes:

in length.

Larger Mexican crystals have transpar-

pleasant appearance but great

Name:

gems

of

rarity.

After the Val Milan Switzerland, because the

mineral was (mistakenly) thought to have occurred there.

to several inches in

length (brownish or reddish massive material). Faceted

gems

in 1968.

ent areas and have been faceted into small

are generally under 3-4 carats in weight; larger

would be extremely rare. A crystal found in 1885 was garnet red in color, weighed 4.4 carats in the rough, and was cut into a stone that looked like a red zircon.

MILLERITE Formula:

NiS.

Crystallography:

Brassy and bronze yellow; tarnishes greenish

Colors:

SI: 3.7 (brown, Virginia).

Hexagonal. Crystals capillary or and cleavable.

acicular; tufted; fibrous; also massive

gray.

Comments: and

is

Microlite

is

usually

opaque

to translucent

cut into cabochons by collectors. Faceted

are very beautiful

gems weighing

and extremely than

less

market and the potential

Name:

From

the

size of the crystals

rare.

Green

found

Brazilian

carat have appeared

to the small

at the original locality.

See: Cancrinite.

Streak:

Greenish black.

Luster:

Metallic; opaque.

on the

exists there for larger stones.

Greek mikros (small), due

MICROSOMMITE MILARITE

1

gems

Hardness:

Cleavage:

2

2 Si 2 4O60

'

Perfect 2 directions. Fracture uneven. Brittle.

Occurrence: A low-temperature mineral in limestones and dolomites, serpentines, and ore deposits in carbonate rocks.

Osumilite Group.

K Ca4Be4Al

5.3-5.6.

Density:

Illinois;

Formula:

3-3.5.

H

2

0.

Wisconsin; Iowa.

Wales; Czechoslovakia; Germany.

MONAZITE Antwerp, New York: fine sprays of acicular crystals. Gap Mine, Lancaster County, Pennsylvania: acicular tufts.

1

fine yellow transparent crystals,

up to

inch long.

Cabochons up to an inch or two can be cut from globular orange and yellow masses from Mexico, and these make unusual and interesting stones. Tsumeb crystals are extremely rare (one pocket found), and most of the crystals are being preserved as specimens and will not be cut. Small broken crystals were cut, yielding some stones up to a few carats in weight, with a maximum of Stone Sizes:

Missouri:

geodes.

in

Gap, Kentucky: tufts of fibers in geodes. Timagami. Ontario, Canada: large cleavable masses.

Hall's

Cabochons

Stone Sizes:

of any size could be cut from

massive material.

Comments: Massive millerite is sometimes cut into a cabochon by a collector or sliced into slabs for decorative purposes. The yellow color is very rich and attractive, and the cut gems are indeed curiosities. The mineral is too soft for wear. Massive millerite is of no great interest to mineral collectors and therefore might be difficult to obtain in the

abundant

Name:

Tsumeb, Namibia:

131

marketplace, although

it

is

at certain localities.

5-7 carats.

Comments: Faceted mimetite is one of the rarest of all gems since only one pocket of transparent crystals has ever been found

who

first

stud-

Tsumeb), and few of these

crystals

colored but are too soft for wear.

Name:

After mineralogist W. H. Miller,

(at

have been cut. Orange and yellow cabochons are richly

From

a

Greek word meaning

because

imitator,

of the resemblance to pyromorphite.

ied the crystals.

MOHAWKITE MIMETITE Formula:

Apatite Group, Pyromorphite series.

PbslAsCMjCl.

tals acicular; globular; botryoidal.

Sulfur yellow, yellowish brown, orange-yellow,

Colors:

orange, white, colorless. Luster:

Ca

replaces Pb.

Brown, reddish brown, yellowish brown, pink,

Vitreous to subadamantine; resinous; waxy.

Hardness: Density:

o

Biaxial (— );

= 2.147; e = 2.128. may sometimes be

Optics:

uniaxial.

0.019.

Weak

Pleochroism: Spectral:

in

Occurrence:

1

direction,

a = 1.774-1.800; fi= (+),2K= 11-15°.

Higher refractive index yellow shades.

Orange-red

Birefringence: in

sometimes

perfect. Frac-

LW (Tsumeb, Namibia).

is

y=

1.828-1.849.

accompanied by lower

A secondary mineral in the oxidized zone

Pleochroism: material

=

0.049-0.055. Faint or

Sri

Lanka

Extremely complex spectra observed, mostly

Spectral:

Pennsylvania.

rare earth types.

USSR: Czecho-

none (yellowish shades).

reddish orange/golden yellow.

of lead deposits.

Scotland: Sweden: France: Germany:

1.777-1.801;

birefringence.

Not diagnostic.

Luminescence:

Distinct

ture conchoidal to uneven. Brittle.

Biaxial

Birefringence:

5-5.5.

4.6-5.4.

Cleavage:

Brittle.

Optics:

sive, granular; detrital.

to resinous.

None. Fracture subconchoidal to uneven.

Cleavage:

Monoclinic. Crystals small, tabular, Crystallography: wedge-shaped; faces often rough or uneven; also mas-

Luster:

if

.

yellow, greenish, grayish white, white.

3.5-4.

7.24, lower

Density:

(Ce,La,Y,Th)P0 4

Colors:

Subadamantine

Hardness:

MONAZITE Formula:

Monoclinic (pseudo-hexagonal). Crys-

Crystallography:

See: Algodonite.

Luminescence:

None.

slovakia: Australia.

Southwestern United States: many localities. Chihuahua, Mexico: fine globular orange and yellow

Occurrence: An accessory mineral in igneous rocks and gneisses; sometimes in large crystals in granite peg-

masses.

matites; as a detrital mineral in sands.

Mapimi, Durango, Mexico: yellowish globular masses. Cornwall and Cumberland, England: a variety called

Petaca

Norway: Finland.

campylite.

Colorado: fine crystals.

district,

New Mexico:

Amelia, Virginia.

MONTEBRASITE

732

Wyoming:

crystals to several pounds.

Madagascar:

Cleavage:

in fine crystals.

Switzerland: excellent crystals in alpine vein deposits. Sri

Optics:

Lanka: orange pebbles.

Biaxial

Callipampa, Bolivia: good crystals.

Deposits of alluvial material

in Australia, India, Brazil,

Malaya, Nigeria.

Faceted gems would normally be under 5

carats, either

from Swiss crystals or from portions of

from other localities. Facetable material is very and cut stones are absent from all but a few private collections. Large cabochons could be cut from various large crystals that have been found. crystals

rare

Monazite may be

Comments:

partially

metamict, with

Stones can be an attractive yellow or brown

1.79.

color but are usually small.

Name:

From

the

Greek monazein,

of the rarity of the mineral.

(

Birefringence:

to

be solitary, because

Spectral:

direction. Fracture conchoidal.

0.005.

None.

Not diagnostic.

Luminescence:

None.

Occurrence: In veins and cavities in igneous rocks; also forms as hydration product of natural glasses. California: Idaho: Utah: Colorado: Wyoming. Nova Scotia, Canada: Scotland; Yugoslavia: USSR; Japan;

New

Zealand.

Stone Sizes: Cabochons can be cut from nodules that reach a size of about 1 inch. Faceted gems have not been reported.

>

Comments:

MONTEBRASITE

1

a = 1.472-1.483; p = 1.475-1.485; y = 1.477-1.487. + ), 2V = 76-104°. Also optically (-).

Pleochroism:

Stone Sizes:

N=

Perfect

Brittle.

See: Amblygonite.

Compact, fibrous material

weak catseyes. Coloration

MOONSTONE

This

See: Feldspar.

is

in

the material

Crystallography: fibrous, cottony,

•

7H

2

0.

Orthorhombic. Crystals prismatic; compact.

Colorless, white; stained yellowish, pinkish.

Luster:

Vitreous to

Density:

it

to staining.

gems

are

has been reported

as being cut for collectors.

Colors:

Hardness:

due

is

Zeolite Group.

(Ca,Na 2 ,K 2 )(Al2Si,o)024

Formula:

cabbed because

a relatively unexciting mineral, and

equally uninspiring. Nevertheless,

MORDENITE

is

the fibers provide a chatoyancy that sometimes yields

4-5.

2.12-2.15.

Name: From the locality at Morden, Nova Scotia, where first found.

MORGANITE MORION

See: Beryl.

See: Quartz.

silky.

MOSS AGATE MUKHINITE

See: Quartz. See: Epidote.

King's County,

N NAMBULITE

Crystallography:

Triclinic. Crystals prismatic, flattened,

and wedge shaped.

Name: versity,

Streak:

Pale yellow.

Luster:

Vitreous.

Hardness: Density:

After Professor Matsuo

series, Zeolite

3.51.

Formula:

Perfect

Nambu of Tohoku

1

direction, distinct

1

2

cite:

a = 1.707; f} = Biaxial + ),2V= 30°.

Optics:

1.710;

y =

2

Solid solution

Group.

Na (AlSi;tOio) 2H 0. Mesolite: 8H (intermediate in series). Scole3H 0.

Natrolite:

Na Ca2(Al

direction.

Uni-

Japan, for his studies of manganese minerals.

NATROLITE; MESOLITE; SCOLECITE

6.5.

Cleavage:

a strik-

rhodonite.

larities to

Reddish brown, orange-brown, orange.

Colors:

is

and not really like any other gem I have seen. Cut stones would be both extremely rare and quite magnificent, perhaps bearing some simiing orange-red, very intense,

NaLiMrisSimCMOH^.

Formula:

The color of Namibian nambulite

Comments:

SijOio)

'

Ca(Al 2 SbO,o)

2

•

2

2

2

All three minerals are fibrous or elongated zeolite

1.730.

minerals that occur in single crystals or radial aggre-

(

gates. Mesolite crystals are always twinned.

Birefringence:

0.023.

yellowish, reddish).

Weak.

Pleochroism:

Luster: Spectral:

Colorless, white (natrolite sometimes gray,

Colors:

Weak.

Dispersion:

Not diagnostic.

Luminescence:

No

Vitreous; silky in fibrous varieties.

Cleavage:

data.

Perfect 2 directions. Fracture uneven. Brittle.

Luminescence: Some natrolite fluoresces yellow-orange in LW (Germany). Indian mesolite may fluoresce pink (LW); mesolite may fluoresce cream white to green in LW (Colorado). None observed in scolecite.

Occurrence: Nambulite is a rare mineral reported in crystals up to 8 long at the Tunakozawa Mine, Northeast Japan. These crystals are found in veins cutting manganese oxide ores. Much larger crystals, up to approximately 3 cm across, have more recently been found in Namibia, at the Kombat Mine, near Tsumeb. I have seen a completely transparent crystal in a private collection that would yield about 20-25 carats of flawless faceted gems, the largest of these perhaps 10 carats in weight.

mm

Occurrence:

Cavities in basalts and other dark igneous

rocks. Scolecite occasionally forms in schists

zones Colorado;

tact

and con-

at limestones.

New Jersey;

Stone Sizes:

Oregon; Washington. Canada; Greenland: Scotland: Iceland. Ice River, British Columbia, Canada. California: natrolite in San Benito County: scolecite

tially

Crestmore, Riverside County.

Nova

Gems up to about 10 carats could potenbe cut from Namibian crystals.

133

Scotia,

at

NATROMONTEBRASITE

134

Mesolite

Natrolite

Crystallography

Scolecite

Orthorhombic,

Monoclinic,

Monoclinic,

pseudo-tetragonal

pseudo-orthorhombic

pseudo-orthorhombic

2.2-2.26

5 2.26

221-2.29

.473-1.483 1.476-1.486 1.485-1.496

1.505 1.504-1.508 1.506

1.507-1.513 1.516-1,520 1.517-1.523

Hardness

5

Density Optics a

1

P Y

C+]

(+)

(-)

58-64°

~ 80° 0.001

36-56°

sign

2V

0.012

Birefringence

5

0.007

more or less uninteresting, Compact masses, cut into cabochons,

Poona, India: large crystals of scolecite and natrolite,

cleavage, and are white and

some

except for

facetable.

Brevig,

Norway:

USSR: huge

might be more durable due to interlocking of the fibers. minerals can readily be distinguished on the basis of

natrolite.

The

natrolite crystals.

optical properties.

Australia: mesolite. Sicily: mesolite.

Names:

France: natrolite.

Germany: natrolite. Rio Grande do Sul, Brazil: immense crystals of scolecite. Brazilian scolecite reported: a = 1.512; /J = 1.518; y = 1.523; birefringence

=

0.011; S.G.

=

2.21.

Mt. Ste. Hilaire, Quebec, Canada: large natrolite crystals (white, opaque).

Southern Quebec: in asbestos mines, natrolite crystals to 3 feet long and 4 inches across (noi of gem quality). Bound Brook, New Jersey: one find of natrolite crystals, thousands of single crystals well terminated, up to 6 inches long,

many

Stone Sizes:

were known only in stones under the Bound Brook, New Jersey, find. Some of

1

carat until

rarity.

transparent.

mesos, an intermediate position, because of

between

gems over 20

New Jersey). New Jersey); also

carats.

its

Greek

position

and scolecite in chemistry and properfrom the Greek skolex (worm) because a borax bead of the mineral sometimes curls up like a worm. ties.

natrolite

Scolecite

is

NATROMONTEBRASITE

See: Amblygonite.

NEPHELINE (Na,K)AlSi04

Formula:

.

Hexagonal. Crystals stumpy, sometimes

Crystallography:

Natrolites

these crystals cut flawless

Natrolite from the Latin natron (soda) because

of the presence of sodium. Mesolite from the

very large; massive, compact; in grains. Colors:

Colorless, white, gray, yellowish, greenish, bluish,

dark green, brick red, brownish red.

SI: 9.31, 7.9 (colorless,

DG:

7.95 (colorless,

scolecite, 0.98

(India).

PC:

Luster:

Vitreous to greasy.

Hardness:

5.5-6.

15 (Ice River, British Columbia).

Mesolite

is

never found

in large

transparent crystals.

Faceted gems are thus very rare, although the possibility exists that larger crystals

could be found one day. Fibrous

2.55-2.66

Density:

Cleavage:

Indistinct. Fracture subconchoidal. Brittle.

=

material cuts fine catseye gems, but these also are small

Optics:

and

Uniaxial (— ).

fragile.

Scolecite

is

also rare in facetable crystals; areas of

some of the large Indian and Brazilian material might cut gems in the 5-10 carat range, but these specimens are in museums and will not be cut. Other stones would likely be

in the 1-3 carat

range and colorless.

Comments: All three zeolites form elongated crystals; faceted gems are almost always, therefore, elongated emerald- or step-cuts. The New Jersey natrolites are by far the largest known faceted gems in this group. All three minerals are relatively fragile and soft, have good

o

1.529-1.546; e

Birefringence:

0.004.

Not diagnostic.

Luminescence: dull

1.526-1.542.

Low.

Dispersion: Spectral:

=

Medium

orange (Ontario)

Occurrence:

in

light

blue (Germany) or

medium

LW.

Plutonic and volcanic rocks; pegmatites

associated with nepheline syenites.

Julienhaab

district,

Greenland: Langesundsfjord, Norway;

NEPHRITE Germany; Finland; USSR; Burma; Korea. Various localities

in

California: alluvial material, various green shades, in

the United States, especially

Maine

and Arkansas. Ontario, Canada: crystals up to 15 inches long (nongemmy). Vesuvius, Italy; small, glassy transparent grains.

Cabochons of nepheline have been cut

Stone Sizes:

135

boulders up to 1000 pounds. Lander, Wyoming: boulders mottled green with white

— very distinctive

Zealand: Maori Greenstone, in situ and in boulders, usually dark green to black. Fraser River, British Columbia, Canada: dark-colored

in

various sizes; crystals, especially those from Canada,

can reach enormous size but are not attractive. Faceting material is extremely rare and very small.

material.

New

nephrite,

USSR

of which

little

Lake

(at

is

very fine quality.

Baikal): dark spinach-green color with

abundant graphitic black inclusions or spots— very

dis-

tinctive jade, fine color.

A

Comments: brown, or

inclusions.

variety called elaeolite

massive or

gray,

red, green,

is

in crystals filled

with minute

These inclusions produce a sheen

that yields

and very few gems have been

a

Fengtien, Taiwan: spinach green to pea green, in seams in rock; despite abundance of material on market in former years, large pieces are very scarce. Also catseyes

is

the 1-2 carat range or smaller.

Name: From a Latin word meaning cloud because becomes cloudy when immersed in acid. Elaeolite from a Latin word for oil because of its greasy luster.

NEPHRITE

JADE)

(=

Ca (Mg,Fe)

Formula:

2

Cowell, South Australia: material similar to

(Si40n)2(OH) 2

New Zealand:

is

large

amounts

Mashaba

potentially available.

Zimbabwe; Germany; Mexico.

district,

Stone Sizes:

uncommon

Alluvial boulders of several tons are not in certain localities.

Large fine pieces are

always carved, for example, the sculpture Thunder, by

.

Monoclinic. Masses of fibrous crys-

Crystallography: tals,

noted. it

Fibrous variety of Actinolite. 5

light in color.

cut, always in

a catseye effect in cabochons. Facetable nepheline

great rarity,

China (Sinkiang Province): generally

Poland: creamy white to gray-green, with green patches (near Jordansmuhl).

densely packed and very tough.

Donald Hord,

in

Wyoming jade

AMNH displays a

(145 pounds).

huge block of nephrite from Poland

Creamy beige (mutton fat jade) when rich in Mg. Green colors, due to Fe. Brown (oxidized Fe); some-

weighing 4718 pounds. SI displays a boulder of several hundred pounds, sliced open, with a thin slab backlit to show the color.

is dark brown. Also yellowish, grayish brown, yellow-green, black.

Comments:

Colors:

times a surface skin

Luster:

Vitreous to greasy; dull.

tions,

Hardness: Density:

Nephrite colors do not match

in either

With few excepnephrite shades are usually dark and somber, and

variety or intensity the colors of jadeite.

nephrite never attains the fine green of Imperial jade

6-6.5.

The Chinese long ago mastered the art of immense brush pots and statues grace many museums around the world. Of special note is the M. M. Vetleson jade collection that occupies an entire room at SI. Carvings have been done using only (jadeite).

2.90-3.02; usually 2.95.

carving nephrite, and

Cleavage: Optics:

None. Fracture

splintery.

Very tough.

a = 1.600-1.627; y = 1.614-1.641. shows a shadow edge

Biaxial (— ). Usually refractometer at

about

Birefringence:

Pleochroism:

0.027.

Strong dichroism, masked due to the fibrous

nature of the material. Spectral:

side of a jade boulder, leaving the rough shape as a background. Fine use is also made of the weathering skin (brownish) of green nephrite, creating a cameo effect, sometimes displaying great detail and fine workmanship. Catseye nephrite from Taiwan has also been reported. The catseyes are due to parallel arrangement of fibers (ferroactinolite content = 10%). The colors found include greenish to honey yellow, dark green, dark brown and

one

1.62.

Doublet

and 4600; sharp Luminescence:

at

6890, two vague bands at 4980

line at 5090.

black.

None.

P=

The

1.626;

Occurrence: Nephrite is most frequently encountered in the form of rolled boulders.

3.01-3.05.

Wisconsin: gray-green color, not too attractive.

Name:

Alaska: green colors, in very large masses, fibrous (chatoyant).

sometimes

properties are as follows: a

y=

From

1.632-1.637; birefringence

the

= 1.613-1.616; = 0.016; S.G. =

Greek word nephros, meaning kidney;

the rounded, organlike shape of nephrite boulders and

pebbles undoubtedly stimulated people to regard these

NEPTUNITE

736

stones as magical cures for the organs they resembled,

Name:

through sympathetic magic. See also: Jadeite.

it

For Neptune, god of the sea in mythology, because was found associated with aegirine, named after Aegir, Scandinavian god of the sea.

NEPTUNITE +2

Eormula:

(Na,K) 2 (Fe ,Mn)TiSi 4 0i2; (mangan-neptunite

has Mn,Fe'

2 ).

Formula: Monoclinic; crystals prismatic, usu-

Crystallography: ally

square

NICCOLITE

in cross section, lustrous

NiAs.

Hexagonal. Crystals very

Crystallography:

rare; massive.

and very well formed.

Extremely dark red, appearing microscopically black. Transparent in small fragments, otherwise opaque.

Colors:

Pale coppery red; tarnishes black.

Streak:

Pale brownish black. Metallic; opaque.

Colors:

Streak:

reddish brown.

Luster:

Luster:

Vitreous.

Hardness:

Hardness:

Cleavage:

Perfect

a=

1

direction; fracture conchoidal; brittle.

1.690-1.691

7.78.

None. Fracture uneven.

Cleavage:

3.19-3.23.

Density:

Optics:

Density:

5-6.

5-5.5.

;/3

=

1.693-1.700;

y=

1.719-1.736.

Luminescence: Occurrence:

Brittle.

None.

In vein deposits in basic igneous rocks,

usually associated with ores of Ag, Co,

Biaxial (+).

and

Ni.

Sonora, Mexico; Germany; France; Austria; CzechosloBirefringence:

Pleochroism: Spectral:

0.029-0.045.

vakia; Japan.

Sudbury

Not diagnostic.

Luminescence:

district,

Ontario, Canada: in large masses; also

Thunder

at Cobalt,

None.

and the Gowganda

Bay,

Stone Sizes: Cabochons of any desired size could be cut from massive pieces.

Comments: color

Stone Sizes: Neptunite is opaque except in minute fragments, from which tiny faceted stones (under 1 carat) of cut.

The

is

Niccolite

always cut as cabochons.

is

a delicate peachy red and

especially in polished material.

bined with

this

unusual color

is

The

is

metallic luster

hard enough to be worn on bola ties and pendants. sometimes tarnishes to a darker color, but a coat of

clear nail polish

Name:

may

prevent

From niccolum,

this.

the Latin

word

the practical size of gemstones;

NORBERGITE

See:

Humite Group.

display the lovely red color neptunite displays in smaller

fragments.

com-

very distinctive. Nicco-

color intensity limits

opaque blackish stones 20-30 carat range could be cut but would not

The

extremely beautiful,

lite is It

in the

district,

Ontario.

Occurrence: In alkaline rocks and carbonatites but most especially embedded in natrolite in San Benito County, California, where it occurs in spectacular crystals associated with benitoite and joaquinite. Narsarsuk, Julianhaab district, Greenland. Mt. Ste. Hilaire, Quebec, Canada. Kola Peninsula, USSR: mangan-neptunite. San Benito County, California.

deep red color have been

New Jersey.

California; Colorado;

yellow/deep red.

NOSEAN

See: Lazurite.

for nickel.

o OBSIDIAN

VOLCANIC GLASS)

(=

present and former volcanic activity. Nevada; Hawaii. Iceland; Japan.

Formula: Variable composition: Si0 2 approximately 66-72% + oxides of Ca, Na, K, and so forth. Basaltic glass is

~50%SiO

Oregon: some iridescent material is known. Wyoming; notably at Yellowstone National Park. New Mexico: Apache tears, small rounded obsidian lumps

2.

Crystallography:

Amorphous;

usually as

rounded mass-

in

es ejected in volcanic eruptions, as small broken pieces, fine, hairlike filaments (for

example, Pelee's Hair), and

varieties.

Black; gray, banded with brown streaks; rarely

Stone Sizes:

green, blue, red. Basaltic glass

is

black, brown, gray, blue, and blue-green.

Iridescence noted: gold,

silver,

blue, violet, green,

and

Larger pieces of obsidian are available

Comments:

5;

6 for basalt glass.

as beads

None. Fracture conchoidal (best example of brittle. Basalt glass may be

is

an attractive material and

used

1.48-1.51; usually 1.49.

may be

in cutting;

jewelry. Faceted

birefringent.

tive,

Elongated, torpedo-shaped bubbles, round

except

discovered

may be white and resemble snowflakes, hence snowflake obsidian.

Occurrence:

None.

Most occurrences of obsidian used

are in the United States. Obsidian

is

found

in

is

widely used

in

in

jewelry

which are cores

tears,

decomposed ob-

among beginning hobbyists. Some of

in

heat-sensitive, so care

gems tend

to be very dark

man named

See: Feldspar

(=

must be

delicate in

and unattrac-

material was supposed to have been Ethiopia by a

OLIGOCLASE

(Mg)

is

or in the blue and green varieties.

See: Vivianite.

ite

737

is

also rather brittle, so

ODONTOLITE

OLIVINE

gems

areas of

it is

in small sizes

The

Name:

arrangement. Needlelike inclusions may give a silvery sheen. Protogenic silica minerals crystallizing in parallel

Luminescence:

dis-

parent) obsidians are quite rare, these sometimes faceted

bubbles, teardrop-shaped bubbles. Bubbles are often in

the term

popular

by hobbyists. Obsidian

N=

Crystals included in the glass Inclusions:

place in certain

these have been faceted. Green, blue, and reddish (trans-

splintery, brittle.

obsidian

Obsidian

and cabochons. Apache

sidian, are

type of fracture). Very

Isotropic.

in

of unaltered glass in nodular shells of

2.33-2.42; 2.70-3.0 for basalt glass.

Cleavage:

many

plays a wide variety of appearances. Snowflake obsidian.

with spherulites of cristobalite,

Hardness:

to

localities.

Vitreous.

Density:

Fragments range from microscopic

inches across. Carvings up to 8-10 inches could be made.

combinations of these colors, due to inclusions of minute bubbles that reflect light.

Optics:

localities.

Mexico: obsidian abundant, especially banded and sheen

Colors:

this

shells.

Utah: major source of snowflake obsidian.

as flows.

Luster:

white perlite

Arizona; Colorado; California: several

PERIDOT)

to Fayalite (Fe).

Obsius.

Solid-solution series: Forster-

OLIVINE

138

Properties of

Gem

Olivines Birefrin-

%MgO 64.65 57.8 54 51.86 51.2 49.8 49.5

Forsterite

Mogok, Burma Zabargad, Egypt

Norway Tanzania Arizona (light green) Arizona Mexico (light green) Mexico (brown)

498 48.2 49.4

New Mexico Lanka (olive) Lanka (almost colorless) Kenya (yellowish) Kenya (brownish)

48.1

Sri

— — —

Sri

%FeO 1.11

8-10 8.5 7.7 8.2 10.4 8.6 11.0 8.7 10.8 3.6

— — 70.51

Fayalite

a

P

y

gence

Density

2 V-sign

1.635 1.654 1.652 1.650 1.650 1.649 1.652

1.651 1.671

1.670

3.22

82°(+) 86°

1.651

1.669 1.673

0.035 0.036 0.036 0.036 0.034 0.037 0.037 0.033

—

1

—

689 688 686 684 686 689 684 690 688 690 675 686

1

681

1.869

1

879

1

1.669 1.665 1.658 1.665

1

1 1

1

1.671

1.655 1.652

1 1 1

1.671

1

1.660 1.657

1.651

1.640 1.650 1.651 1.827

1 1

322

— — — — — — — — — — — —

3.34 3.30 3.25 3.28

334 3.33

0035

—

0.036

3.33 3.36 3.20 3.45 3.35 4.39

0039 0.035 0.036 0.038 0.052

134°(-)

(Greenish peridots generally have a density of 3.3-3.4; brownish stones about 3.5.)

Mg

Formula:

2

Si0.rFe2Si04. Rarely

Mn

also present.

intrusion; fayalite

is

rare, occasionally

(balls of cristobalite) in obsidian.

Orthorhombic. Crystals rare, usually corroded grains; often as rolled pebbles,

Crystallography: striated prisms,

or in nodules called

bombs

in

for

lemon yellow. green, yellowish, amber brown, brown,

Fayalite:

The

gem

color of olivine

is

due

to ferrous iron.

The

content.

best

San Bernardino County, California; Bolton,

Massachusetts.

Hawaii:

green.

lithophysae

main constituent of basic igneous rocks, and con-

Riverside, olive

in

centrations in basalts and ultrabasic rocks can be mined

volcanic areas.

Forsterite: green, pale

Colors:

are a

seen

Intermediate olivines

in

volcanic bombs.

New Mexico and Arizona: peridot occurs as grains, which

green gemstones have an iron content of about 12-15%.

are used by ants to build large

an unattractive, muddy color. Very bright green colors may result from a trace

erosional fragments from a parent rock,

of Cr.

and stones cut from these fragments are usually small (under 5 carats), with an occasional larger gem. Kenya: brown crystals. Zabargad (Zebirget), Egypt (Isle of St. John): this is the most ancient source for peridot as well as a source of some of the most confusing name mixups in gem literature. Zabargad (Zebirget, Zebirged) is an island in the Red Sea that is often shrouded in fog, making it difficult for ancient navigators to find. The location had been lost, in fact, for centuries and was rediscovered about

More Fe than

Luster:

this results in

Oily to vitreous.

Hardness:

6.5 (fayalite) to 7 (forsterite).

Cleavage:

Imperfect to weak. Fracture conchoidal.

Brittle.

Optics; Density:

Dispersion:

vary with composition.

0.020.

None

Pleochroism:

away. Peridot

1905.

The

Fayalite: greenish yellow/orange-yellow/greenish yellow.

now eroded

mined on the Navajo Indian Reservation,

island

is

located 35 miles off the Egyptian

coastal port of Berenica. Crystals of peridot are found in

veins of nickel ore in an altered peridotite rock.

color of the

Glass balls that look

gem

material

is

a

medium

The

green, not too

dark, and very rich.

None.

bubbles in Hawaiian material; some U.S. localities contain inclusions of Cr-spinel (not magnetite as previously thought); also Inclusions:

these grains are

in forsterite.

Peridots: weak, green to yellow-green.

Luminescence:

is

hills;

like

noted are biotite grains, and lotus leaves, which are petal-like liquid inclusions around Cr-spinel crystals.

Occurrence: Forsterite occurs in magnesian limestones that have been altered by heat and pressure from igneous

Burma: peridot

is found in masses on the slopes of Kyaukpon, near Mogok. The material yields dark green,

oily

gems

of fine color, transparent,

hundred carats

in size.

This

is

some

of several

the world's only major

source of very large peridot.

Norway: peridot is found at Ameklovdalen, Sondmore. The gems are paler than from other localities and are of a lovely lime-green hue because the material contains

OPAL less Fe. Cuttable pieces are very rare in large size and seldom yield cut stones over 5 carats. Mexico: one of the world's largest deposits of olivine is located in the state of Chihuahua. The material is similar to Arizona peridot but also occurs in brown grains. Emali, Kenya: gem quality. Ratnapura, Sri Lanka: olive-green gems; also nearly colorless material that is the closest in composition to forsterite of any gem olivine known. Mt. Batchelor, North Queensland, Australia: yellowgreen, dark green, gemmy; potential for stones up to about

of green depending

gems

139

on the

locality of origin. Brown commonly seen but can be when the color is more golden

rich in iron are not

very beautiful, especially

than brown.

Names:

Chrysolite from the Greek, meaning yellow

stone. Forsterite after is

named

Forster, a mineralogist. Fayalite

J.

after the Fayal Islands in the

Azores because

it

was believed to occur there in volcanic rocks. Olivine from the Latin oliva (olive) because of the similarity in color. Peridot is from the thirteenth-century English peridota.

20 carats.

Umba district,

Tanzania: Minas Gerais, Brazil: Ross Island,

some

Antarctica:

USSR: Finland:

cuttable material. Italy;

Germany: Greenland: New

ONYX

See: Calcite, Quartz.

Caledonia.

OPAL Peridot shows a strong iron spectrum, with

Spectral:

three

main bands: strong

4530; there are also

at

at

some vague bands

5290, but the set of three evenly spaced bands

at is

6-10%

6530 and

distinctive.

Burmese material cuts the

largest

gems,

'

is

«H

2

0. Water

= 1-21%

in opal, usually

precious opal.

composed

cles, that

followed by Egyptian material. Peridot from Antarctica is

in

Crystallography:

opal

Stone Sizes:

Si0 2

Formula:

4930, narrow at 4730, broad

is,

Amorphous. Recent work shows

that

of an aggregate of tiny spherical parti-

a solidified gel; often forms concretions;

botryoidal; reniform; stalactitic.

limited to a few stones under 2 carats. Arizona material

over 10 carats

is

Colors:

very rare in cut form.

Colorless, white, yellow, orange,

and red (various

310 (Egypt); 287 (Burma); 22.9 (Arizona). ROM: 108, 87.1, 83.3 (Burma). DG: 82.4, 24.7 (Burma).

shades), yellowish brown, greenish, blue, gray, black, violet.

PC: 284.85

Hardness:

SI:

(Egypt); 34.65 (Arizona).

Geological Museum, London: 136 (Burma). Topkapi Museum, Istanbul: many large and fine cabochons.

Density:

Optics:

Catseye and star peridots are known but

are very rare.

The low hardness

ringstones will

of peridot

show scratches rather

means

rapidly

There

is

intermediate

members

of the

considerable variation in shade

Spectral:

White Park,

Cliffs,

Green fluorescence minerals.

Much

SW, LW, sometimes with

in

Nevada

Quartzite, Arizona

pale yellow is

persistent phosphores-

LW medium

Queretaro, Mexico

opal often due

Opal

phosphorescent dull white; phosphorescent bright green dull white;

in

opal fluoresces strong

cence. (See table below.)

Australia

Opal may also fluoresce brownish Black opal

U

SW

Wyoming

Virgin Valley,

in

1.44-1.47.

as low as 1.37, usually 1.42-1.43.

Luminescence: white

N=

Brittle.

None.

to included

Fluorescence Locality

and

Very low.

Dispersion:

that

if it is struck a sharp blow. Peridot is an ancient gem, often referred to as chrysolite, a term

in referring to

Isotropic;

and mav

sional stone to split

olivine series.

None. Fracture conchoidal.

Mexican opal

become badly chipped. The cleavage may allow an occa-

used

1.99-2.25; orange-red variety -2.00; black

Cleavage:

collection.

Comments:

5.5-6.5.

white opal, 2.10; green opal, 2.12.

An immense clean crystal of more than 100 carats from Norway (by far the largest known) is in a European

still

Vitreous, waxy, pearly.

Luster:

blue,

phosphorescent

strong white; phosphorescent bright blue;

phosphorescent

medium

green, blue-white; phosphorescent bright pale yellow

generally inert Fire opal luminesces greenish

brown

Common opal often fluoresces green.

OPAL

740

Moss

OPAL TERMINOLOGY

opal: white to brownish

opaque opal

that con-

tains dendritic inclusions.

Siliceous sinter; geyserite: massive, glassy opal that

forms around hot springs and geysers; no gem significance.

Diatomaceous earth;

tripoli: fine-grained,

powdery

Menilite:

opaque gray

to

Tabasheer: opaline

bamboo.

agents,

billowy light effect within

Pseudomorphs: opal may,

in percolating

through the

ground, replace (on a microscopic or even cellular basis)

wood, bone, and Hyalite:

Girasol: opal that

Chrysocolla

occurring

silica

masses of opal or the siliceous remains of microscopic marine animals called diatoms. Often used as polishing fillers.

brown opal with a concre-

tionary structure.

almost transparent and has a it, resembling moonstone.

is

in opal:

in the joints of

blue material, with finely dissem-

inated chrysocolla that gives the color.

Liver opal: term sometimes used for brown

shells.

transparent, colorless, or white to gray

opal, glassy, occasionally faceted but generally

no gem

Resin opal: yellowish brown

waxy

significance.

common

opal.

common

opal with a

luster.

Common opal: opaque or glassy opal, in a wide range sometimes with a waxy luster; often fluoresseldom cut into gems. Water opal: transparent, colorless opal that may have

of colors, cent;

fire in

fire refers to the

magnificent play of

color displayed by opal, which is due to light diffraction from neatly stacked layers of the microscopic spheres of which opal is composed. Common opal is a jumble of

spheres of random sizes, but in precious opal the spheres are the

same

size,

and they are layered in neat rows. The depends on the size of the spheres

particular color seen

and the angle of viewing. Fire opal: transparent to translucent red or orange opal,

which may or may not have

fire in

it!

The term

Onyx opal and agate cious and

colors displayed.

White opal: white body-color opal, usually with play of color.

Gray opal: light to dark body color, with play of color superimposed. Black opal: black body color with fire, often spectacular against dark background. Body color also very dark bluish, greenish, or brownish. Semiblack opal: another way of describing gray opal. Milk opal: milk white, translucent, also yellowish or greenish in color. Crystal opal: water opal or milk opal, generally rich in

transparent to translucent in transmitted light; col-

ors seen by reflected light.

Contra-luz opal: very rare type, usually from Mexico,

with color play

concentrated

in the

In catseye opal the color play

is

form of an eye or band. Matrix opal

consists of specks of precious opal in a rock matrix,

usually sandstone; this type of opal is often dyed black to enhance the color play. Ironstone opal is in a brown, hard, compact type of sandstone. Matrix opal may also

be layers or stringers of opal in a rock matrix. Flame opal: sweeping reddish streaks and bands move across the gem, resembling flickering flames. Flash opal: as the gem is moved back and forth,

and disappear at various spots. Harlequin opal: the color display is in the form of angular or quiltlike patches, all in contact with each other, like a mosaic. flashes of color appear

Pinfire opal: the color

form of

Peacock opal: many colors appear

tiny dots

or

Also gold opal (gold

tail

fire),

in the

same gem,

of the male peacock.

blue opal (bluish

fire),

lechosos opal (green colors).

Occurrence:

In sedimentary rocks or

temperature solutions bearing

silica

where low-

can percolate through

rocks.

Honduras: deposits known since before 1843, perhaps older than that. Occurs as veins in dark reddish to black trachyte rock. White opal contrasts strongly with the dark-colored matrix. Pieces not large, seldom very

much

jasper.

The

to the tongue. Prase opal: translucent or opaque green opal; a common opal resembling prase.

in the

resembling the display of the

spectacular.

Cachalong: porcelaniferous, often bluish-white, very

is

speckles, set close together.

in both transmitted and reflected light. Hydrophone: light colored, opaque, becomes iridescent and transparent when soaked in water. Jasper opal: reddish-brown opal, opaque, resembles

porous— adheres

opal: alternating layers of pre-

common opal.

fire

opal refers to a body color, not to play of color. Precious opal: opal of any color with fire or play of

fire;

DISTRIBUTION IN OPAL

it.

The term

Note:

TERMS FOR COLOR AND COLOR

Czechoslovakia: source of opal

known

in

near the village of Czerwenitza (formerly

Roman in

times,

Hungary).

Opal occurs as seams in grayish brown andesite rock. opal is a mosaic of strong colors and is very attractive, against a milky-white background color. Much of this

is

harlequin opal.

Indonesia: very

dark rock.

little

Much of it

is

known

material, as thin

seams

in

water opal and resembles mate-

OPAL from Mexico. The white opal resembles poor-grade Some black opal is produced that is very unusual and consists of reddish flecks of color swimming in a translucent but very dark brown body. Most gems are very small (less than 10 carats) from this locality, and

141

rial

Andamooka, South

Australian.

1930; very distinctive opal, white and also brownish in

production

is

very small.

Brazil: opal occurs in sandstone in Piaui State, north-

ern Brazil, and also near Manaus, northern Brazil. is

good-quality Australian white opal.

I

The

white and fiery and sometimes resembles

most durable opal, low

in

gem

have seen a cut

may be artificially blackened -to enhance the appearance of the fire in the matrix. White Cliffs area: started about 1889, but the opal is color;

usually small, with veinlets of precious opal within

Mexico: Mexican opal occurs in siliceous volcanic lavas, in cavities, and in many localities. Yellow and red fire opal comes from a trachyte porphyry at Zimapan in Hidalgo. Hyalite and precious opal that is completely transparent, colorless, and rich in fire occurs at San Luis Potosi, Chihuahua. Queretaro is a well-known opalproducing locality. Fine Mexican opal is very rare in large sizes (over 50 carats) but is among the most beautiful. Virgin Valley, Nevada: opal occurs in Humboldt County as cracks and seams in opalized wood. This was discovered about 1900. The opal is magnificent, but is very hydrous and has a strong tendency to crack due to loss of water when exposed to the air. This behavior is known as crazing, or, when on the surface, checking. Whole skeletons of extinct animals have been replaced by fine precious opal at this locality. Similar opal is found in Idaho.

material

Australia: opals found here about

It

is

perhaps the

water and not heat sensitive—

held for a half a minute over a

candle flame with no adverse

effects.

The

material seems

be abundant and much of it is shipped to Hong Kong where it is cut and sold, often as Australian opal. Poland: green prase opal, colored by nickel.

mon

com-

opal.

Gabanintha (Murchison Goldfield): bright green opal, is found in quartz. Mintabie: mined since 1931, about 350 km northwest of Coober Pedy. This area has now been extensively colored by copper,

prospected. Australia

is

the best

known opal-producing area in

the

world, but the deposits have been worked so intensely

becoming depleted. Many fewer miners are the opal fields than 10 years ago, and new discoveries are rare. This factor, plus worldwide demand, is putting tremendous pressure on opal prices. that they are

now working

Stone Sizes: Like diamonds, many large and fine opals have been given individual names. Only a few are included here; others are described in books specifically about opal.

Olympic Australis: Coober Pedy; uncut was 127 ounces. Noolinga Nera: Andamooka; 86 ounces rough, cut 205 carat oval.

Roebling Opal: Rainbow Ridge, Nevada, 2610

(in SI).

Light of the World: Lightning Ridge, Australia, 252, partly cut.

Red Admiral or Butterfly: Lightning Ridge, possible 40-50 carats in rough. Many regard this gem as the world's most

to

Tanzania: nickeliferous opal resembling chrysoprase

occurs

in

Tanzania, associated with brown limonite.

R.I. (1.452) is

is

The

lower than that of chrysoprase (1.535), as

the gravity (2.125 versus 2.620). Stone sizes tend to

be small.

beautiful opal.

Pride of Australia: Lightning Ridge, 226, partly cut. Pandora: Lightning Ridge, 711, cut.

first

discoveries were probably about

1850, but major finds were 1872. Australian opal

is

made

in

Queensland about

in various types:

143.2 (orange, precious, Mexico); 55.9 (colorless, pre-

Virgin Valley opals at SI include the Roebling Opal

(19 ounces).

ROM:

69.58 (Contra-luz, Mexico).

Comments:

layers of opal in between.

gems.

Yowah

nuts: walnut-sized concretions, in a regular layer,

conglomerate.

The opal

is

the central kernel and

never reaches the outer edge.

Seam

opal: thin to thick

in

sandstone matrix. Also known as sandstone opal. Large stones are very rare

Major

known from

Opal

is

one of the most popular of

is

black opal, which all

is

opal varieties.

the size of the stone, the colors

pattern of the color. Opal prices to advertising is

the loveliest and

The it

in

nodules, world's finest of

and the

may also vary according

and the fashion of the time.

hydrous, and

crack spontaneously.

It

when it dehydrates, it tends to may crack or craze immediately

after,

at any time thereeven after a period of many years! Opals kept in

may suddenly develop minute, The only way to prevent this is to keep

mined commercially about 1905. Coober Pedy, South Australia: discovered about 1915;

jewel cases and drawers

only white opals found here, in sandstone and claystone

opals perpetually in a jar of water, which

this material; first

some very

value of opal

displays,

upon being taken from the ground or

specific localities:

Lightning Ridge: black opal

matrix, but

all

very rare in large sizes (over 30-40 carats);

most expensive of

Opal

in this material.

finds of Australian opal are best

It is

especially rare

lies in

seams of white or black opal

white); black

cious, Mexico); 39 (pale yellow-orange, precious, Bra-

Boulder opal: shells of coarse, hardened, sandy clay with

like a

(all

opals of 58.8, 54.3, and 44. Also 355 (black, Nevada);

zil).

Australia: the

gems; 345, 155, and 83

SI: Australian

fine.

threadlike cracks.

Much

of the value of an opal

is

lost

is

inconvenient.

when cracking occurs

ORBICULAR JASPER

742

since the cracks seriously impair the strength of the

and may allow

to

it

The hardness

fall

of opal

low for a gem used

is

opal

and are

damaged beyond

lost.

it

is

as such.

Frequently an opal

is

very

not a good ringstone,

repair, or

Many

crack and

in a ring

is

opals fall

in

out

found to be

lifeless; this may be due solely to a network of scratches on the surface that destroys the polish and reduces the color play. The opal can be fixed by simple repolishing. Opal is usually very brittle and heat sensitive, so great care must be used in cutting to prevent cracking. Opals (or any other gems, for that matter) should not be worn while washing dishes because of the thermal shock of the hot water. Opal may have excellent color play but occur as very thin seams in rock or in white opal without fire. These seams can be utilized by cementing them to a backing material such as potch opal (without fire), obsidian, or a ceramic, using a black epoxy cement. The black cement makes the colors appear stronger. Such a composite

chalk white and

stone

is

known

as a doublet.

If

Bits of precious opal are

sometimes suspended

in tiny

glass or plastic spheres or tear-shaped vials in water or

only about 5.5, which

in jewelry;

but people persist in wearing rings are

gem

out of the setting.

a quartz

cabochon

(usually) glycerine so they float slowly

jewels are

Many

known

and

These

types of opal can be treated to enhance their

A common

appearance.

technique

is

to

immerse white

Andamooka) in sugar solustrong sulfuric acid. The acid carbonizes

or gray opal (especially from tion

and then

in

the sugar and leaves microscopic carbon specks in the opal,

which

effectively blacken the

body color and make

the spots of fire stand out better. Opal has been synthesized by Pierre Gilson of France

and

is

and Inamori of Japan,

imitated by a variety of other materials, including

plastics

Name:

and

glass.

Opalus was the ancient Latin name of

this

gem,

probably derived from Sanskrit upala. meaning precious stone.

The Greek

opallios literally

means "to see a change

of color."

ORBICULAR JASPER

See: Quartz

is

cemented on top of the opal layer, the stone is called a triplet and is a three-layer sandwich with opal in the middle. Triplets are good ringstones because the quartz is hard and protects the opal from scratching.

gently.

as floating opals.

ORTHOCLASE

See: Feldspar.

ORTHOFERROSILITE

See: Enstatite.

PAINITE Ca^AhoBSiO^.

Formula:

Hexagonal, pseudo-orthorhombic.

Crystallography:

Color:

would display the almandine spectrum, a very definitive test. This is perhaps the rarest of all gem species — not a single cut stone is known to exist, and only a few crystals have ever been identified! tested. Also, a garnet of this color

Dark

red, garnetlike in hue.

Name: Luster:

Hardness: Density:

PALYGORSKITE

8.

o

=

1.816; e

=

many

1.787.

0.029.

Pleochroism:

= deep

o

ruby red; e

=

pale brownish

orange. Faint

Inclusions:

Minute

of complexly

Weak

Burma,

red

in

in the

Luster:

Dull; translucent.

LW, strong red

in

rial;

SW.

misidentified as ruby or garnet.

The

is

2.1-2.2.

Easy; not observed on impregnated mate-

Around

1.55 (probably reading values for quartz

Occurrence: Palygorskite is a product of alteration and occurs in hydrothermal veins, serpentines, and granitic rocks.

Attapulgas, Georgia: Metalline Falls. Washington.

Scotland; England; France;

USSR: Morocco.

Peru; Mexico: angel stone.

Comments:

This material has been marketed as angel-

skin opal, but this

so clearly

could not be confused with garnet,

is

impregnation) for angel stone.

refractive indices

are unlike those for ruby, and the material

2.21 (pure); angel stone

tough.

Optics:

gem gravels of Mogok. One

Comments: No cut gems are known. The first discovered specimen is the red crystal in the British Museum in London, weighing 1.7 grams. The color resembles garnet, and the density is that of garnet or ruby. This means that there might be cut gems in existence that have been

it

White, gray, rose pink, pale pink, yellowish.

Cleavage:

mineral.

birefringent that

Colors:

Density:

cavities in thin sheets; inclusions of

red crystal was discovered in 1951 and identified in 1957

new

made up

Hardness: Pure material very soft (around 2); angel is impregnated with silica and hardness = 4.5.

Cr spectrum.

Luminescence:

as a

0.

skin

tabular hexagonal crystals (phlogopite).

Occurrence:

2

intergrown fibers, resembling parchment or leather.

Birefringence:

Spectral:

4H

polytypes. Crystals very elongated, in bundles;

usually thin flexible sheets

Uniaxial (— ).

= ATTAPULGITE.

Monoclinic and orthorhombic, with

Crystallography:

Not determined.

(Angel Stone)

(Mg.AlhSi^OH)

Formula:

4.0.

Cleavage: Optics:

After the discoverer, A. C. D. Pain.

Vitreous.

is

a

misnomer

as the material

gether different from opal. Angel stone

if

743

is

is

alto-

a microcrystaline

;

PAPAGOITE

744

quartz impregnating manganiferous, pale pink palygorskite.

PARGASITE

The

bole; Series to Ferropargasite

silica

impregnation makes the material hard and

durable enough to cut. Palygorskite lite

(meerschaum) and

is

related to sepio-

structurally contains amphibolelike

The parchmentlike, matted aggregates of

silicate chains.

fibrous crystals typical of palygorskite have led to the

rock-wood and mountain-wood or

fanciful designations

The

mountain-leather. tractive

color of angel skin

and the material

is

very

is

suitable for both

Palygorskite after a locality in the Urals,

NaCa

Formula:

USSR

Colors:

6

2

(OH)3. tiny, flattened;

usually microcrystalline coatings and aggregates, some-

times mixed with quartz.

Cerulean blue; leaves no streak.

Luster:

Vitreous.

Hardness: Density:

5-5.5;

3.25

if

may be approximately may be lower

pure;

Distinct

if

on

(for

7

a =

Biaxial (+), 2

1

1.613;

V=

Birefringence:

direction; parting 2 directions.

/3

=

y =

1.618;

1.635.

120°.

0.022.

Colorless/ very light brown/light brown;

crystals;

example, 2.42

brittle,

Luminsecence: Occurrence:

not observed on microis

Not diagnostic.

tough

mixed

if

None.

A widespread component of igneous and

metamorphic rocks. Pargas, Finland.

Fresno, California; Burlington, Pennsylvania.

USSR;

Scotland; Sweden; 1.607;

=

/?

1.641;

y =

1.672.

Baffin Island,

Stone Sizes:

Birefringence:

faceted

0.065.

None

Pleochroism:

Occurrence:

Nova

Scotia,

Austria; Venezuela.

Canada.

Pargasite from

gems in

Nova Scotia has yielded

the 2-3 carat range.

The mineral, though

abundant and widespread, seldom occurs reported.

Bands centered

Luminescence:

None

at

parent enough for cutting stones over

4480, 5150, and 5550.

reported; inert in

LW and

SW.

Orignally found as tiny crystals associated

Pima County, Arizona. This was not mixed with quartz was reported from a locality near Elko, Nevada. This is hard, tough, and takes a high polish making it suitable for cabochons. A regular interlocking structure is visible under magnification, and tiny metallic copper crystals may also be noted. The material is similar in appearance to chrysocolla or turquoise. Cabochons are translucent to opaque with a with ajoite at Ajo,

cuttable. Material

Stone Sizes: Cabochons up to several inches can be cut from the massive material.

in

length

For the Papago Indian tribe that lived region around Ajo, Arizona.

in the

in crystals trans-

V2 carat.

The amphibole group is very large and extremely complex and contains numerous distinct speComments:

and physical properand ferropargasite are calcic amphiboles that generally are lumped together as hornblende, even though up to 16 distinct minerals belong to this group,

cies that vary subtly in chemistry ties.

Pargasite

including actinolite (see page 37).

amphibole

The

identity of a

determined (ideally) by a chemical analysis or by detailed measurements of density, color, and optical data. There are undoubtedly a great many localities that could potentially yield cuttable crystals. specific

Name:

vitreous luster.

Name:

Perfect

silicified.

Biaxial (— ).

Spectral:

3.069-3.181.

Spectral: if

with quartz.

a =

brown, grayish black, bluish

colorless/bluish green/bluish green; greenish yellow/green/

mixed with quartz.

crystalline material; pure mineral

Optics:

to

bluish green.

on Arizona material) Cleavage:

Monoclinic; crystals prismatic, also

5-6.

Pleochroism:

Colors:

.

Vitreous.

Luster:

Optics:

Monoclinic; crystals

Crystallography:

(Mg,Fe)4Al(Si 6 Al2)022(OH) 2

brown

Light

Cleavage:

CaCuAlSi

Formula:

if

green, dark green.

Density:

PAPAGOITE

also: Actinolite;

massive, compact or granular.

Hardness:

attapulgite after the locality in Georgia.

2

Crystallography:

at-

cabochons

and carvings.

Name:

Hornblende; AmphiFe exceeds Mg. Amphibole Group; closely related to Hornblende. See

is

After the locality, Pargas, Finland.

PARISITE Formula:

Ca(Ce,La) 2 (C0 3 )3F 2

Crystallography:

.

Hexagonal; crystals double hexago-

PEARL nal pyramids, often steep, sometimes prismatic, sometimes rhombohedral.

striated;

this is

Brownish yellow, brown, grayish yellow.

Luster:

Vitreous to resinous; pearly on basal cleavage

surfaces.

Density:

4.5.

Distinct basal parting or cleavage; perhaps

to alteration. Fracture

subconchoidal to splintery;

brittle.

Acids:

test.

None. Fracture uneven. Roughness

Cleavage:

Optics:

pearls, 2.85; cultured pearls,

heavier than most natural pearls, but

not a diagnostic

N=

shadow edge

4.36.

Cleavage:

is

variable.

0.156 (aragonite).

1.53-1.69, but not observed; usually

vague

in this range.

Pearls will dissolve in

Luminescence:

all

Natural pearls

acids.

may be

light blue,

LW, SW. Cultured pearls natural in LW. Freshwater pearls

yellowish, greenish, or pinkish in

o=

Optics:

Uniaxial

is,

Birefringence:

Hardness:

conch

2.6-2.78;

2.72-2.78, that

Colors:

due

Density:

145

(

1.676;

e=

no reaction, or same

1.757.

as

always glow yellowish white

+ ).

Birefringence:

Pearl Colors:

0.081.

The

in X-rays.

surface tone or orient

due

is

to dif-

fraction at the edges of overlapping plates of aragonite

Weak.

crystals at the surface.

Not diagnostic.

roughness when a pearl

Pleochroism: Spectral:

Body Colors:

Not reported.

Luminescence:

These edges cause a feeling of is rubbed across the teeth.

White, as follows: white (no overtone); cream (no over-

carbonaceous shale beds in the emerald deposits of Muzo, Colombia: also as typical inclusions in emerald crystals. Also in alkali pegmatites in Norway. Muzo, Colombia. Langesundsfjord, Norway. Italy; Madagascar; Manchuria. Quincy, Massachusetts; Ravalli County, Montana. Occurrence:

In

Stone Sizes:

Parisite

is

a rare mineral,

usually very small. Tiny faceted stones

and crystals are under 1 carat)

(all

After

J. J.

Paris, proprietor of the

where the mineral was

first

cream

to light yellow; light rose (pinkish

overtone on white background); cream rose (cream back-

ground with deep rose overtone); fancy pearls (cream background, with overtone of rose; blue or green secondary overtone seen at edges of pearl). Black: includes gray, bronze, dark blue, blue-green, green. Some have metallic overtones. Colored Pearls: neither black nor white, usually with a blue background color, plus red, purple, yellowish, violet, blue, green.

More

frequently seen in freshwater

pearls.

have been cut from Montana material.

Name:

tone); light

mine

at

Muzo

discovered.

Darker colors are apparently due to dark conchiolin core of a pearl showing through the thin layers of

in the

aragonite crystals.

Shapes of Pearls:

PEARL

Round; pear-shaped (squat = egg

shape, elongated pear

= drop shape);

button

(flat

back);

Formula: CaC0 3 aragonite), about 82-86%; conchiolin, 10-14%; water, 2%.

with

These proportions are

grain); dust pearls (almost microscopic); blister pearls

(

variable.

Orthorhombic (aragonite), with the minute crystals radially oriented and a concentric structure.

Crystallography:

Colors:

The

color of a pearl

a result of a

is

and an overtone color (known as

body color

orient) present (due to

surface effects) as a lustrous sheen.

The

orient

color seen as reflected by a diffuse light source. of the color observed

is

due

in full view, the

The

the

other at the edge.

flat area);

Pearly, dull.

Hardness:

2.5-4.5.

(% round

less

than

V4

(attached to shell); baroque pearls (any irregular shape not mentioned); slugs (baroque pearls with a poor luster).

Occurrence: Salt-water pearls are the most important on the market. These come principally from the species of oyster

known

as Pinctada.

Persian Gulf: the world's major pearl-producing area, especially close to the coasts of Iran,

Oman, and Saudi

Arabia. These waters have produced pearls for more

than 2000 years. Persian Gulf pearls are usually small (less than 12

The diving season is roughly May-September, and the waters are worked by hundreds of small boats. The diving depth is about 30-90 feet but usually less than grains).

Luster:

seed pearls (unsymmetrical,

rest

body color. There are one seen on the surface

to the

sometimes two overtone colors,

is

half pearls (flat back); three-quarter pearls

PEARL

146

60

recovered from oysters, washed, and

feet. Pearls are

then sold to merchants

in

Bombay,

India.

Then

follows a

throughout the world, including Europe, South

rivers

America and the United

States.

bleaching operation (using hydrogen peroxide and sun-

are

light), sorting, grading, and drilling. Poor-quality pearls go the Far East, in general. Better pearls go mostly to Paris and from there many reach the United States.

France: Germany; Austria.

Bombay

Amazon

is

chiefly a brokerage center.

Persian Gulf pearls are creamy white. Density

is

Notable occurrences

in:

Scotland; Wales; England; Ireland. Mississippi River and

Nova

tributaries.

its

River Basin.

Scotia.

East Pakistan.

2.68-2.74.

Gulf of Manaar: an arm of the Indian Ocean, between Lanka and India. The waters have been fished for pearls for more than 2500 years, but fishing now is sporadic. The government of Sri Lanka controls the fishing and auctions the oysters that are caught. The oysters are opened by leaving them on the ground to rot, and the decomposition products are searched for pearls, which then go to Bombay. Gulf of Manaar pearls are pale cream white, sometimes with fancy overtones of blue, green, and violet. Density is 2.68-2.74. Red Sea: not a major pearl producer today. The pearls are reputed to be whiter than those from other sources. Sri

Australia: pearl oysters are fished off the west, north-

west, and north coasts.

Armored

used. Recovery of the shells

is

diving suits are

now

as important as recovery

of the pearls since the shells provide a major industry.

Patents for processes to produce cul-

Cultured Pearls:

tured pearls were granted

in

Japan about 1910. The basic

work was down by Otokichi Kuwabara, Tatsuhei Mise, Tokichi Nishikawa, and Kokichi Mikimoto. The process developed involves the insertion of a bead of mother-ofpearl (shell) up to about 13 mm in diameter, along with a piece of tissue from a part of the oyster known as the mantle, into the body of the oyster. The oysters upon which the surgery has been performed are allowed to convalesce in sheltered waters for 4-6 weeks. They are then allowed to grow, in cages, for a period of 3-6 years at a depth of 7-10 feet. Nacre accumulates around the inserted bead to form a pearly layer. Japan

is

the world

leader in cultured pearl production.

Cultured blister pearls are half-pearls formed by accu-

is

mulation on a half-bead stuck to the shell of the oyster. Large-diameter beads can be used. After pearl growth,

South Seas: native fisheries operate around Micronesia and Polynesia. The pearls may be large (up to 7100 grains!) and are generally round. Tahiti is the major pearl

the nacrous (pearly) dome is removed and cemented onto a mother-of-pearl bead. This product is called a

Australian pearls are silvery white to yellow. Density 2.67-2.78.

center.

The

colors are usually white with

also can be yellow, gray, cast

is

and black.

A

little

orient but

metallic, grayish

characteristic.

Japan: Japanese waters are rapidly becoming too polluted for the existence of Pinctada. Cultured pearls now constitute a

much

bigger industry. Japanese pearls are

white, often with a greenish tinge. Density

is

2.66-2.76.

Mabe pearl. Some cultured pearls are grown Biwa, Japan, using clams. As

in fresh

many

water

in

Lake

as 30 insertions per

clam can be tolerated without killing the animal. Growth requires about 3 years, and the pearls have excellent color and luster. Externally, cultured and natural pearls are virtually identical. Identification requires skilled use of special

such as the pearl endoscope or X-ray apparatus.

Venezuela: Venezuelan oysters are usually small varie-

tools,

and the pearls vary in color from white to bronze, also black. White pearls from here may be very iridescent and almost glassy. Density 2.65-2.75. Mexico: Panama: fisheries here are small and not impor-

X-radiography offers the only positive proof of the origin of a pearl. Other tests are helpful but not conclusive.

tant commercially.

Hope

Florida; Gulf of California: occasionally pearls are found,

circumference

ties,

which are pink (from conch shells). Pearls are also found in abalone, and colors may be green, yellow, blue, and other tones. California has produced black pearls. Density of Florida pearls (pink) is about 2.85; California, 2.61-2.69. Abalone shells are

especially

conch

pearls,

often hollow inside with bright iridescent colors that

make them very distinctive. Conch shells are often used to make cameos. Conch pearls are usually pink, with a very distinctive flamelike surface pattern.

Freshwater Pearls: come from a mussel called Unio, rather than from oysters. Freshwater pearls are found in

One

Stone Sizes:

This

Pearl

is

metric carat

BM

in the

at the

is

Pearl

is

4 pearl grains The

2 inches long, 4.5 inches in

broad end, and weighs 1800 grains.

a salt-water pearl, perhaps of

The Queen

Burmese

origin.

of freshwater origin, pink, round,

translucent, weighs 93 grains,

New

=

and was found near Paterson,

Jersey!

pear-shaped and weighs 1191 grains. La Pellegrina, a very famous pearl from the Orient, weighs

Miracle of the Sea

is

111.5 grains. Other notable pearls include: La Peregrina (Panama), 203 grains. The Gogibus (West Indies), 504 grains. La Regente, 337 grains.

Pearl of Asia, 2420 grains.

PECTOLITE The

following table gives the approximate weights (in

grains) of pearls of

Diameter

mm

silky.

sizes:

Hardness:

4.5-5.

2.74-2.88.

Density:

mm

in

Vitreous to

Luster:

147

Weight

Cleavage: 1

2 3 4

0.02 0.25

Optics:

075

Biaxial

1.75

5 6

3.50

7

9.75 14.5 19.5 28.0 38.0 48.0 61.0 81.0 101.0

about

6.0

8 9 10 11

12 13 14 15

(

Perfect

1

direction. Fracture splintery.

a = 1.595-1.610; /}= 1.605-1.615; y = 1.632-1.645. + ), 2 V= 50-63°. Refractometer spot reading at

1.60.

Birefringence: Spectral:

0.036.

Not diagnostic.

Luminescence: In LW, orange-pink (Bergen Hill, New cream white (Lendalfoot, Scotland). In SW, greenish yellow (Scotland), yellowish, orange with green areas (Magnet Cove, Arkansas, and Lake County, California),

Jersey),

faint yellow with

phosphorescence (Paterson,

New Jersey).

Occurrence:

Maximum

Comments: large pearls. irritant

beauty

is

not usually found

in

They form, basically, by encapsulation of an

by tissues of a mollusc.

The

value of pearls

is

a

function of color, luster, orient, translucency, texture,

shape, and especially

size.

Groups of

pearls, such as

beads, create complex valuation problems because degree of matching

becomes an

issue.

The

price of a group of

determined by a complex formula involving a base price multiplied by the square of the weight in grains. The base rate is higher for higherquality and for matched pearls. In addition, there are ways of averaging sizes to determine the overall size to use in the formula for groups of pearls. The base rate is a fluctuating market factor, determined by experience. pearls or a single pearl

The

is

introduction of cultured pearls early in this cen-

tury caused a major depression in the prices of pearls

since high-priced, rare, natural pearls could not initially

be distinguished from cultured ones.

many

The market took

years to recover, and with unambiguous labora-

tory tests

now

available, fine pearls have recovered their

In cavities in basaltic rocks, associated with zeolites; in lime-rich metamorphic rocks.

USSR; Morocco;

Scotland; Sweden; Czechoslovakia;

South Africa; Japan.

New Jersey:

Paterson area,

Franklin and Sterling

in fine radial sprays; also at

Hill.

Alaska: massive, jadelike (used as jade substitute); also fine-grained, pale blue-green.

Lake County, California: dense material suited

for

cabochons.

Magnet Cove, Arkansas:

pinkish manganiferous material.

Canada: Thetford Mines, Quebec; Asbestos. Quebec: magnificent prismatic crystals, some facetable, also twinned, up to 5 inches long; pale blue-green color. white.

Greenland: manganiferous.

Dominican Republic: compact, white, and various shades of blue (sometimes dark) material capable of cutting

cabochons with high polish Stone Sizes:

(larimar).

Cabochons up

to a

few inches have been A few small

cut from dense, massive, or fibrous material.

and market than natural pearls. Large (over 12 mm) pearls of fine color and orient are very rare and costly, and even more so if available in original esteem. Cultured pearls are fully accepted

occupy a

larger share of the

1.705

matched groups.

Name:

From

PECTOLITE

the Latin

word penda, meaning pearl.

Series to Serandite (through

Mangan-

pectolite).

Formula:

NaCa

Crystallography:

2

Si 3 08(OH)

+ Mn.

Triclinic. Crystals acicular, radial or

globular masses; often terminated. Refractive index vs. composition

Colors:

Colorless, white, gray.

series.

in

pectolite-serandite

PENTLANDITE

748

gems have been cut from material found at Asbestos, Quebec, about 1973. These are the only known faceted pectolite gems; they range in size up to about faceted

commonly

Comments:

ity for collectors.

enough

a curios-

is

The fibrous agregates are seldom coheand the material

to cut,

is

too soft and fragile

for wear, unless the fibers are intergrown.

could be jadelike

Such material

toughness as well as appearance.

in

When sufficiently compact, cabochons take an excellent The material from Quebec is extremely

transparent crystals are usually

rare,

Isometric. Crystals octahedral, cubic;

rounded

grains.

The local trade name for the material is Larimar; it and, though locally abundant, this is a rare gem material. The blue color is due to copper. the

Vitreous.

Luster:

Hardness: Density:

5.5.

3.56.

Cleavage:

tiny.

cent.

From

Colorless, white, gray, yellow, brownish yellow,

Colors:

green, black.

and

Dominican pectolite is the loveliest in the world; it is compact and takes a very high polish. It is colored in various shades of blue, and the finest is dark and translu-

Name:

as

Fibrous material has a chatoyancy that

gives a catseye effect to cabochons. Pectolite

polish.

MgO.

Formula:

Crystallography:

3 carats.

sive

PERICLASE

Greek pektos, meaning congealed

Optics:

Perfect Isotropic;

Luminescence: Occurrence:

direction. Fracture uneven. Brittle.

1

N=

1.736.

Pale yellow in

Occurs

in

LW

(Terlingua, Texas).

marbles, due to high-temperature

contact metamorphism.

New

Texas;

Mexico.

Spain; Sardinia; Czechoslovakia.

embedded grains.

because of the translucent appearance the mineral some-

Crestmore. Riverside County, California:

times has.

Vesuvius, Italy: as glassy grains in the lava rocks.

Nordmark, Sweden:

(Fe,Ni) 9 S 8

.

Isometric. Crystals extremely rare; mas-

Crystallography:

periclase

masses

Light bronze yellow.

Bronze brown.

rarity

A

due

rough. Luster:

known

mines.

in transparent, large crystals.

Periclase has been synthesized in large

in the laboratory,

icance.

Streak:

not

is

Comments:

sive, granular.

Color:

Mn

Stone Sizes: I have not seen any faceted gems, but if such gems existed, they would be very small. Transparent grains from Vesuvius might be cuttable, but in general

PENTLANDITE Formula:

in the

but these have no market signif-

faceted natural periclase would be a great to the

extreme scarcity of suitable faceting size would be less than 1 carat.

The expected

Metallic; opaque.

Name: Hardness:

3.5-4.

Cleavage:

None. Fracture conchoidal.

Luminescence:

to break around,

Brittle.

PERIDOT

None. Nonmagnetic.

Associated with pyrrhotite and other nickel

Occurrence:

From the Greek peri plus klastos,

in allusion to the cleavage.

See: Olivine.

PERISTERITE

See: Feldspar.

ores in basic rocks.

Norway;

Transvaal, South Africa; Alaska; California;

PERTHITE

Nevada.

See: Feldspar.

Sudbury, Ontario, Canada: major ore mineral, huge masses.

PETALITE

Stone Sizes: Cabochons of any desired size can be cut from massive material.

Formula:

Comments:

Crystallography:

lic

Pentlandite resembles other yellowish metal-

minerals and

is

cut by collectors as a curiosity.

The

ally

tite

is

usually intimately intermixed with pyrrho-

and chalcopyrite

in

Canadian ore bodies, creating an

interesting, multicolored metallic appearance.

Name:

After

J.

B. Pentland

who first noted the

Monoclinic. Crystals rare, tabular; usu-

Colors:

Colorless, white, gray, yellow, sometimes red-

dish or greenish white, pink.

Luster:

mineral.

.

massive, cleavable.

cut stones are quite attractive but too soft for hard wear.

Pentlandite

LiAlSi 4 Oi

Vitreous to pearly.

Hardness:

6-6.5.

PHOSGENITE Density:

Cleavage: Optics: Biaxial

(

Perfect

=

1.510-1.521;

y= 1.516-1.523.

0.012-0.014.

Cleavage:

Indistinct,

o=

Optics: at

4540

Uniaxial

(

In

LW

be orange

pale orange

(Wyoming) or buff

Dispersion:

Observed

Pleochroism:

Arassuahy, Brazil: large, clean masses.

sionally pale rose.

Zimbabwe: considerable material mined

1.670.

0.005.

for

Bikita,

direction. Fracture conchodial.

0.016.

in X-rays.

In granite pegmatites, in crystals

e=

1.654;

and masses. North Bonneville, Wyoming; Greenwood, Maine; San Diego County, California; Bolton, Massachusetts. Uto, Sweden; Elba, Italy; USSR. Londonderry, Western Australia: facetable material. Occurrence:

1

+ ).

Birefringence:

Luminescence:

May

2.93-3.00.

Brittle.

stones.

(Maine).

7.5-8.

Density:

direction. Brittle.

Not diagnostic; may be a vague band

Spectral:

some

1

a =1.503-1.510;/} + ),2V= 83°.

Birefringence:

in

Hardness:

2.3-2.5.

149

example,

in a

in

strongly colored crystals;

greenish-blue stone: violet-red/intense

blue.

Not diagnostic.

Spectral:

Luminescence:

for Li

Pale greenish or blue in

UV light, occa-

Sometimes fluoresces blue

in X-rays.

Crystals of aikinite; also mica (Brazil).

Inclusions:

content. Karibib, Namibia: colorless, transparent, and pinkish

Occurrence:

material.

Pala County, California; Colorado (Pike's Peak area);

up

about 20 carats from Brazilian crystals and smaller from other localities. Some Brazilian and Namibian rough has yielded Stone Sizes:

somewhat

Petalites are usually small,

to

larger stones in the 50 carat range.

SI: 55 (colorless, Namibia); 48.3, 45.9, 26.6 (colorless,

In granite pegmatites, often in

DG:

Hampshire; Lord's Hill, Maine. Kragero, Norway; France; Switzerland; Czechoslovakia; Usugara district, Tanzania; Klein Spitzkopje, Namibia. Habachtal, Austria: small

PC: 48.25

Most faceted petalites are colorless and They are desirable because of their rarity

glassy looking.

and

if

colorless or yellowish

up

to 2 inches across.

reddish color.

San Miguel de Paracicaba, Brazil: tals, often clean and cuttable.

(colorless).

Comments:

gemmy

crystals.

USSR:

14.8 (colorless, Australia).

Crystals up to 5

Stone Sizes:

x

10

large colorless crys-

x

18

cm

have been

found, though these are usually heavily flawed.

they are free of inclusions, especially in large sizes.

A considerable number of

crystals.

New

Virginia: crystals Brazil).

good

largest

known rough was

a pebble found in Sri

The

Lanka

1-10 carat faceted gems from been available on the market. Massive pink material from Namibia is occasionally cabbed.

that weighed 1470 carats and cut a 569 carat clean gem and several smaller stones. The large stone has many

Name:

SI: 22.2 (colorless,

Brazil have

needlelike inclusions.

From

the

Greek

petalos, (leaf), in allusion to

the cleavage. Castorite, the after Castor,

name

applied to crystals,

one of the heavenly twins

in

is

Greek mythol-

ogy (see Pollucite).

NMC: PC:

21.21, 19.17 (colorless,

Comments:

WOOD

See Quartz.

PHENAKITE

Name:

Hexagonal. Crystals rhombohedral, prismatic, acicular; also granular, and in fibrous spherulites.

Crystallography:

Colors: red,

all

Colorless; also yellow, pink, brown, pinkish

due

to surface stains;

by impurities. Luster:

Vitreous.

Phenakite

is

USSR).

but

it is

very hard and suited for wear

colorless

carat range.

Be 2 Si04.

Formula:

(colorless, Brazil).

and not exciting to look at. Cut gems have little fire but are very bright. Red gems cut from material from the USSR are seldom seen and are very rare. The normal faceted gemstone is in the 1-5 in jewelry,

PETRIFIED

USSR); 21.9

23.41 (colorless, Brazil).

some

crystals are colored

From

the

Greek

for deceiver

because

it

was

mistaken for quartz.

PHOSGENITE Formula:

Pb 2 C0 3 Cl

Crystallography:

2

.

Tetragonal. Crystals prismatic, thick

and tabular; massive, granular.

PHOSPHOPHYLLITE

750

Colorless, white, yellowish white, gray, shades

Colors:

of brown, greenish, pinkish.

Hardness:

Luminescence:

6.13.

Cleavage:

1

direction. Fracture conchodial.

=

=

2.114-2.118; e

2.140-2.145.

Very weak, reddish/greenish, only

in thick

Strong yellowish fluorescence

in

UV

Occurrence: A secondary mineral in lead ore deposits. California; Colorado; Arizona; New Mexico; MassachuTarnow, Poland;

USSR; Tasmania;

Australia; Tunisia.

Sardinia: fine yellow-brown crystals up to 5

inches across;

some have

Phosgenite

almost always

less

brown

facetable areas.

very rare as a faceted gem,

is

than 2 carats, and usually yellowish

color (Sardinia).

in

A

few larger stones, up to

about 10 carats, are known.

Comments: ing

Massive material can be cut into

cabochons of various colors, up strong fluorescence

is

Comments:

Phosphophyllite possesses a color almost gems, a lovely blue-green shade enhanced by cutting. This is a very rare mineral. Stones are seldom available because of lack of incentive to cut up good in

Few

crystals.

large stones exist; the material

shown

too soft to wear.

quite

the Bolivian material to be

almost Mn-free, unlike the

of interest to specialists in

is

and fragile and very difficult to cut, with an easily developed cleavage. This is one of the more desirable of the collector gems as well as one of the more expensive brittle

to the size of the

is

5.25 (Bolivia).

ones. Analysis has

German

material that con-

Mn.

Name:

After Greek words for phosphorus-bearing and

cleavable.

From phosgene, a name for the compound COCl

2

(carbonyl chloride) because the mineral contains C, O,

and

about 3

74, flawless (Bolivia).

DG:

interest-

fluorescent minerals.

Name:

to

SI: 26.9 (Bolivia).

tains

rough (several inches). Phosgenite

The

up

refractive indices of this material 1.597-1.621,

crystals have

unique

Tsumeb, Namibia: some cuttable. Stone Sizes:

and

Only Bolivian material has been cut, but been found that could yield stones of about 75 carats or more. These are superb and very rare crystal specimens and will undoubtedly never be cut. Most stones are in the 1-10 carat range, cut from crystal fragments and broken crystals.

PC:

setts.

Mat locks, England;

f Bolivia)

Stone Sizes:

some

Monte Poni,

In massive sulfide deposits

Hagendorf, Germany: small crystals associated with secondary phosphate minerals.

pieces.

Luminescence: and X-rays.

SW.

density 3.08, fine blue-green color, transparent.

0.028.

Pleochroism:

in

pegmatites (Germany).

in granite

X 2 inches;

Uniaxial (+). Birefringence:

Fluoresces violet

Potosi, Bolivia: magnificent single crystals

sectile.

o

Optics:

Occurrence:

Distinct

Somewhat

None.

Not diagnostic.

Spectral:

2-3.

Density:

0.021-0.033.

Pleochroism:

Adamantine.

Luster:

Birefringence:

PICOTITE

See: Spinel.

CI.

PICTURE JASPER

See: Quartz

PHOSPHOPHYLLITE Zn (Fe,Mn)(P0 4

Formula:

2

Crystallography:

)

2

4H

developed.

Colors:

Colorless to blue-green.

Luster:

Vitreous.

Density:

Cleavage: Optics: Biaxial

PIEDMONTITE

See: Epidote.

PLAGIOCLASE

See: Feldspar.

0.

Monoclinic. Crystals prismatic to tab-

ular, well

Hardness:

2

PLANCHEITE

PLASMA

See: Shattuckite.

See: Quartz.

3-3.5.

PLEONASTE

See: Spinel.

POLLUCITE

Series to Analcime; Zeolite Group.

3.08-3.13.

Perfect

1

direction. Fracture uneven. Brittle.

a = 1.595-1.599; /3 = {-),2V= 45°.

1.614-1.616;

y=

1.616-1.621.

Formula:

Cs,

xNa AlSi 2

(Cs,Na) 2 (Al 2 Si 4 )0 12

v

H

2

6

Q.

xH 0;x ~ 2

0.3.

Also written:

PREHNITE Isometric. Crystals cubic, very rare;

Crystallography:

dal (faces often striated), also tabular; massive, foliated,

pulvurent, ocherous.

massive, fine-grained. Colorless, white, gray; tinted pale pink, blue,

Colors:

151

Straw yellow, greenish yellow, pale greenish

Colors:

blue, blue, blackish blue, dirty white (grayish) to gray,

violet.

brown, blackish.

Vitreous, slightly greasy.

Luster:

Subadamantine

Luster:

Hardness:

6.5-7.

Hardness:

to greasy (on fracture surfaces).

3.5-4.

2.85-2.94.

Density:

Optics:

4.23 (varies with tungsten content); Indian

Density:

None. Fracture conchoidal.

Cleavage:

Brittle.

material 4.26 (colorless) to 4.28 (brown).

N=

Isotropic;

Dispersion:

1.518-1.525.

Cleavage:

Indistinct; fracture

0.012. to pink fluorescence in

UV

Uniaxial

(

1.967-1.974; e

=

brittle

and fragile.

1.978-1.985.

+ ).

Birefringence:

Usually whitish, resembling spikes or balls,

Inclusions:

=

o

Optics:

Orange

Luminescence: and X-rays.

uneven;

Dispersion:

0.011. 0.058.

very small; also very tiny snowflakes, bulging at the

Pleochroism:

centers.

Occurrence: In granite pegmatites. San Diego County, California; Middletown, Connecticut. Bernic Lake, Manitoba, Canada; Elba, Italy; Finland; Kazakhstan, USSR; Karibib, Namibia. Custer County, South Dakota: massive material in thick seams. Newry, Maine:

Various localities

in

(N —

Stone Sizes: Masses in South Dakota reach 3-4 feet in thickness, opaque, whitish. Gems are usually colorless and very small; Maine material cuts stones from masses that reach a size of 10 inches. SI: 8.5 (colorless, Maine); 7.0 (colorless, Connecticut). PC: 3.85 (pinkish, Maine).

it

is

Pollucite

is

a very rare cesium mineral. In

the only mineral in which

constituent.

Gems

Cs

is

an essential

are always very small, under 10 car-

ats,

despite the existence of large beds at

It is

colorless and lacks fire

its

when

cut but

some localities. is

yel-

A secondary mineral in the oxidation zone material.

Utah; Nevada; California; Arizona; New Mexico. Pandulena Hill, Nasik, India: unique occurrence, scattered crystals associated with zeolite minerals in basalt cavities.

Turkey;

USSR; Morocco.

The Michigan

Stone Sizes:

material

yield extremely minute stones, rial

gem

was found powellite was

and

is

cuttable only to

until the Indian

essentially

mate-

unknown

as a

The Indian crystals are quite transparent and cuttable, and gems up to about 3 carats have been cut. These are among the rarest of collector gems. material.

Name:

After the American explorer and geologist, John

Wesley Powell.

PRASE

Pollux was, along with Castor, a brother of Helen

Greek mythology. This mineral was found in Italy in 1846, and named pollux; it was associated with another mineral, named castor, which was later studied and renamed petalite.

of Troy in

POLYCRASE

Luminescence: Fluoresces yellowish white-golden low in both LW and SW.

of interest for

great rarity.

Name:

blue/green (Michigan);

Houghton County, Michigan: blue cuttable

Maine and Massachusetts.

1.518, S.G. 2.90).

fact,

is

yellow/light yellow (India).

of ore deposits.

material.

Varutrask, Sweden: massive lilac to white material

Comments:

is

Not diagnostic.

Spectral:

Occurrence:

gem

Blue material

yellow material

See: Euxenite.

See: Quartz.

PREHNITE Ca Al2SbOio(OH)2 +

Formula:

2

Crystallography:

Fe.

Orthorhombic. Crystals prismatic and

tapering, rare; massive, in druses and crusts, stalactitic.

Colors:

Pale green, dark green, yellow, yellowish green,

gray, white, colorless.

POWELLITE Formula:

Luster:

Ca(Mo,W)04.

Crystallography:

Isostructural with Scheelite.

Tetragonal; crystals usually pyrami-

Vitreous to pearly.

Hardness: Density:

6-6.5.

2.80-3.00;

gem

material usually 2.88-2.94.

PROSOPITE

752

Cleavage: Optics: Biaxial

(

Distinct

1

direction. Fracture uneven. Brittle.

a = 1.61 1-1.632; /J = 1.615-1.642; y = 1.632-1.665. + ), 2V = 65-69°. Usually refractometer gives

shadow edge about

Colors:

Colorless, white, gray.

Luster:

Vitreous.

Hardness:

4.5.

1.63.

Note: Faceted material from Australia, indices 1.618/ 1 .625/ 1 .648; birefringence 0.030. Values for optical con-

Density:

2.88.

Cleavage:

stants increase with increasing iron content.

Perfect; not seen

on massive material;

frac-

ture conchoidal.

0.021-0.033.

Birefringence:

a =

Optics:

Pleochroism: Spectral:

None.

Biaxial

Not diagnostic.

May

Luminescence: and X-rays.

in

UV

mineralization.

California; Colorado; Michigan; Massachusetts; Connecticut.

France: Italy; Austria; Germany; kia;

South Africa; Pakistan;

New

in basalts, associated

USSR; CzechoslovaZealand.

=

/J

1.503;

y =

1.510.

0.009.

None.

Pleochroism:

Not diagnostic.

Spectral:

None

Luminescence:

reported.

Occurrence: In tin veins, alkalic pegmatites, and as an alteration product of topaz in volcanic rocks. St. Peters Dome, El Paso County, Colorado: cryolite deposit.

Dugway due

district,

Tooele County, Utah: greenish color

to a trace of copper.

Santa Rosa, Zacatecas, Mexico: associated with azurite;

with zeolites.

blue material.

Fairfax Quarry, Centreville. Virginia: fine green material.

Asbestos. Quebec, Canada: in acidic dikes, in crystals up

Germany; Tasmania.

to 3 inches long (colorless).

Stone Sizes:

Scotland: facetable.

gem

Prosopite

is

a nondescript mineral of no

significance, except for the beautiful blue material

from Zacatecas, Mexico. This material

Australia: facetable.

Stone Sizes: Large masses, up to several tons in size have been encountered in New Jersey traprocks. Single masses weighing 400 pounds have been collected. Australia and other localities produce translucent material that yields interesting faceted

DG:

1.501;

+ ).

Birefringence:

be dull brownish yellow

Occurrence: A low-temperature mineral occurring by deposition from goundwaters in basaltic rocks associated with zeolites; hydrothermal crystals, in cavities in acid igneous rocks; in serpentine rocks due to late-stage

New Jersey:

(

gems up

to

about 30 carats.

38.20 (yellow, Australia).

is

turquoise-blue,

with density variable from 2.69-2.85. Distinction from

on the lower refractive index Mexican prosopite is evenly colored due to approximately 1.4% copper content. It makes an effective and attractive turquoise substitute. turquoise

is

chiefly based

(1.50 vs. 1.62 for turquoise).

Name:

From a Greek word meaning a mask, in allusion when found as

SI: 4.4 (yellow-green, Scotland).

to the deceptive nature of the material

Comments: Prehnite is popular as a cabochon material among hobbyists because of its lovely green and

pseudomorphs.

blue-green to yellow colors. Completely transparent material is

extremely rare but might be found

in crystals

from

PROUSTITE

Dimorph

Asbestos, Quebec. Yellowish to greenish translucent mate-

Formula:

from Australia has been faceted and makes a striking cut gemstone with a rich color and interesting appear-

Crystallography:

of Xanthoconite.

AgiAsSv

rial

ance, with a soft, velvety look.

Some catseye stones have

Hexagonal (R). Crystals prismatic, rhombohedral; massive, compact.

also

been reported. Material from Scotland has yielded cuttable fragments, but such faceted gems are rather

Colors:

Deep

small (under 5 carats).

Streak:

Bright red.

Luster:

Adamantine

Name: After Colonel Hendrik von Prehn, who found the material on the Cape of Good Hope.

first

PROSOPITE Formula:

CaAl (F,OH) 8 2

Crystallography:

commonly

.

Monoclinic; crystals minute, tabular;

massive, granular.

red, scarlet to vermilion red.

Hardness:

2-2.5.

Cleavage:

Distinct

uneven. Optics:

1

to submetallic.

direction. Fracture conchoidal to

Brittle.

o

=

Uniaxial (— ).

3.088; e

=

2.792.

PUMPELLYITE Birefringence:

Cleavage:

0.296.

No

Strong in shades of red.

Pleochroism:

153

Distinct in 2 directions. Fracture splintery.

cleavage

massive material.

in

a = 1.674-1.702; /} = L675-r.715; y = 1.688-1.722. Biaxial (+) and (— ), 2V= 26-85°. May show anomalous birefringent colors. Mean index ~ 1.7.

Optics:

Not diagnostic.

Spectral:

Luminescence:

None.

Low-temperature ore deposits or the upper

Occurrence:

portions of vein deposits.

Pleochroism:

Sarrabus, Sardinia.

Cobalt

Ontario, Canada: small crystals.

district,

Mexico: small

Batopilas, Chihuahua,

Germany:

Freiberg,

sometimes

ties,

crystals.

fine crystals; other

and large

in very fine

/}:

German

locali-

some

crystals,

cuttable.

is

unique.

from Chile, but cuttable crystals in private collections and museums are not about to be cut up. Occasional fragments from

Germany

bluish green/pale green/brownish yellow.

y: colorless/pale yellowish

are transparent.

proustite

Gems

is

weighing several hun-

dred carats could be cut from crystals on display various museums.

The

finest proustites

collection of the British

Museum

known

in

are in the

of Natural History,

London. SI: 9.9 (red,

Germany).

Comments:

Proustite

brown/brownish yellow.

Note: Pale-colored pumpellyite has low birefringence, weak dispersion, and lower indices. Dark-colored pumpellyite has higher values for all these properties.

Luminescence:

None.

Not diagnostic.

Spectral:

Most cuttable

Stone Sizes:

Distinct, as follows:

a: colorless/pale greenish yellow/pale yellowish green.

Dolores Mine, Chanarcillo, Chile: world's finest proustite occurs here, in crystals of deep red color, often transparent, up to 6 inches long and very thick. The occurrence here

Moderate.

Dispersion:

Idaho; Colorado; Nevada; California.

Moderate.

Birefringence:

Occurrence: Pumpellyite occurs in a wide variety of igneous and metamorphic rocks and environments. Scotland; Austria; Finland; USSR; New Zealand; South Africa: other localities.

Calumet, Michigan: in copper ores; also at Isle Royale, Lake Superior, Michigan (non-gem) and on the Keweenaw Peninsula, Michigan (non-gem). Lake Superior: basic igneous rocks on the periphery of the lake contain spherical aggregates of green fibers of chlorastrolite, in masses. This material

is

one of the most sought-after of

but

is

collector minerals because of its magnificient color and the brilliance of good crystals. It is far too soft for wear, and exposure to light causes it to turn black (a photochromic effect due to the silver present) so the

New Jersey:

material should not be displayed in strong light. Faceted

to 2 inches long.

gems

small sizes, yielding stones less than

all

deep red with a metallic surface that and distinctive. One of the rarest of

are

beautiful

is

both

all

the

better-looking collector gems.

Name:

After

J.

L. Proust, a

California: in

glaucophane

Stone Sizes:

Comments:

Ferropumpellyite: contains ferrous iron.

effect

Also note: Julgoldite: con-

pattern

2

H

dense mats of random

Colors:

Green, bluish green, brown.

Luster:

Vitreous; silky

Hardness: Density:

is

best observed

when

when

packed

resulting in a

2

0.

fibrous.

in

3.18-3.33; chlorastrolite: 3.1-3.5.

turtle-back

is

many

to

move within is

a

the stone

common

parts of the world, but fine green mate-

scarce and greatly prized by collectors. is

The

best

a very intense green resembling the color of fine

emerald or Imperial jade. Good-quality chlorastrolite with strong pattern and color

Name: geologist

6; chlorastrolite: 5-6.

seems

changed. Pumpellyite

color fibers.

The

considered most desirable and, because of the

is

fibers,

mineral

shell.

the fibers are in radial

chatoyancy of the

Monoclinic. Crystals fibrous, flattened

plates, in clusters or

typically forms aggregates of

as the lighting

rial is

Crystallography:

It

mixed with other minerals,

iron.

Ca2MgAl2(Si04)(Si 2 07)(OH)

inch long.

The gem variety of pumpellyite, chlorasknown from the Lake Superior district of

clusters that yield circular markings.

PUMPELLYITE (= CHLORASTROLITE)

Formula:

1

green and white pattern reminiscent of tortoise

See: Serpentine.

and ferrous

is cut as cabochons up to 1 Very fine deep green material occurs in

the United States.

The

tains both ferric

schists.

Chlorastrolite

fibers that are

PSEUDOPHITE

sometimes cut

in basalts (traprocks).

trolite, is best

French chemist.

is

not homogeneous.

is

now

difficult to obtain.

Pumpellyite after Raphael Pumpelly. Michigan

who

did pioneering studies of the

Keweenaw

Peninsula copper district of Michigan. Chlorastrolite

from Greek words meaning green star stone.

is

PURPURITE

154

PURPURITE

(Mn,Fe)P0 4

Formula:

Orthorhombic. Crystals masses and cleavages.

Deep

to

5.85.

Cleavage:

.

Crystallography:

Colors:

Density:

Series to Heterosite.

uneven,

Distinct

rose to reddish purple; alters on outside

=

o

Optics:

3.08; e

Luster:

Dull, satiny.

Birefringence:

Optics: Biaxial

(

1

direction. Fracture uneven. Brittle.

a = 1.85; p = 1.86; y = + ), Immoderate.

1.92.

0.007.

Very strong. Strong: gray/rose-red or deep red/purplish

None

Luminsecence: Occurrence:

In

reported.

low temperature hydrothermal vein

deposits, as an important ore of

silver.

Germany; Guadalajara.

Freiburg.

Pleochroism:

None observed.

Not diagnostic.

Spectral:

3.69.

Dispersion:

0.200.

Pleochroism:

4-4.5.

Birefringence:

made using Na line at

5890)

Uniaxial (— ).

Good

2.88.

the Li line at 6710 rather than the customary

Reddish purple.

Cleavage:

=

(Note-these reported measurements were

Streak:

Density:

direction. Fracture conchoidal to

rare, in small

brown or black.

Hardness:

1

brittle.

Spain.

Mexico: Guanajuato and Durango. Colorado; Idaho; Nevada; California. Ontario, Canada; Czechoslovakia; Chile. Colquechaca, Bolivia: fine crystals, gemmy.

red.

Not diagnostic.

Spectral:

Comments:

Luminescence:

None.

Occurrence: A secondary mineral, due to the oxidation of phosphates in granite pegmatites. South Dakota; California; North Carolina. France; Portugal; Western Australia. Usakos, Namibia: rich purplish masses.

Pyrargyrite

is

found

in a

number

of locali-

well-formed crystals, but these are usually small.

ties in

However, larger, transparent crystals from Bolivia and Chile have provided a limited amount of cuttable rough. Stones approaching 50 carats have been cut, but these tend to be too dark to be really attractive. They are exceedingly rare, however, since pyrargyrite is seldom transparent, usually even less so than the related sulfide, proustite.

Stone Sizes: Cabochons up to several inches long can be cut from cleavages.

PC: 40

Comments:

allusion to the color

and composition.

PYRITE

Dimorph

of Marcasite.

Formula:

FeS2.

This material is never transparent and is too soft for wear. However, cabochons are a magnificent purplish rose hue that have essentially no counterpart in the gem world. The material is available from Namibia in abundance and at low cost.

Name:

After the Latin purpura (purple), in allusion to

(shield-cut, Bolivia)

Name:

From Greek words meaning fire and

Crystallography:

Isometric. Crystals abundant and wide-

spread, sometimes very large and displaying an

the color.

silver, in

immense

variety of forms; also massive, granular.

PYRARGYRITE

Color:

Formula:

Streak:

Greenish black.

Luster:

Metallic; opaque.

AgjSbSj. Related to proustite.

Hexagonal (R); crystals prismatic, often hemimorphic. Usually massive, compact, disseminated.

Crystallography:

Colors:

Dark

red.

Streak:

Purplish red.

Luster:

Adamantine.

Hardness:

2.5.

Brassy yellow, sometimes with iridescent tarnish.

Hardness: Density:

6-6.5.

5.0-5.03.

Cleavage:

Indistinct. Fracture

conchoidal to uneven.

Brittle.

Other

Tests:

Nonmagnetic; insoluble

in

HC1.

PYROXMANGITE Occurrence: The most abundant of all sulfide mineroccurs in nearly all rock types and most geological environments. Localities too numerous to list in detail. Fine crystals are known from the following localities: Leadville, Colorado; French Creek, Pennsylvania; Bingham, Utah. Elba, Italy; Ambassaguas, Spain; England; Austria; Germany: Switzerland; Sweden; Peru; Bolivia. als;

Cabochons

Stone Sizes:

of any size could be cut from

the large crystals that have been found. Pyrite

seen with

in

is

usually

inexpensive jewelry, faceted in rose-cut fashion

Comments: gold and

is

Pyrite

is

as fool's

familiar to nearly every mineral collector. in

It

jewelry and as an ore

of iron. "Marcasite" stones in jewelry are frequently pyrite, since the latter

is

very brittle and heat sensitive

Cabochons

The material and requires some care

more

stable.

are sometimes cut, but they have

From the Greek word emits sparks when struck like a

for fire,

Mexico; Sweden; Belgium; USSR; Korea.

Brazil;

South Africa: so-called koranna stone, which dark gray and is about 86% pyrophyllite; R.I. ~ 1.58, S.G. 2.72; also called South African Wonderstone. Transvaal,

sive material,

Cabochons and carvings are cut from masany practical size.

Comments:

Pyrophyllite resembles talc in

Stone Sizes:

and

is

many ways

indistinguishable by eye from soapstone.

needed

is

to distinguish

Chemi-

them. North Carolina

often used in carvings, as

is

the material from

China known as agalmatolite.

Name:

From

the

Greek words

for fire and /ea/because and thermal properties of the

of the sheetlike nature

mineral. Agalmatolite

means figure stone,

in allusion to

is

its

use in carvings.

in

no

special appeal.

Name:

North Carolina; Penn-

is

material

more commonly known

has been used for centuries both

cutting.

Minas Gerais,

Switzerland; Japan;

cal tests are

popular during the Victorian era.

River,

sylvania: Georgia.

backs, similar to the older marcasite jewelry

flat

Deep

California; Arizona;

155

because pyrite

PYROXMANGITE (Mn,Fe)Si0 3

Formula:

Triclinic. Crystals tabular; usually

Crystallography:

flint.

.

mas-

sive, in grains, cleavable.

PYROCHLORE PYROPE

See: Microlite

Reddish brown, dark brown, pale to rose pink, The darker colors are due to alteration.

Colors:

purplish pink.

See: Garnet.

Vitreous to pearly.

Luster:

PYROPHYLLITE Formula:

Hardness:

AhSiiO.otOHh.

Density:

Monoclinic. Crystals tabular, often curved and deformed; foliated, radial, granular, compact.

5.5-6.

3.61-3.80.

Crystallography:

White, yellow, pale blue, grayish green, brown-

Colors:

Optics:

Biaxial ish green.

Perfect 2 directions. Fracture uneven. Brittle.

Cleavage:

a = 1.726-1.748; /J= (+),2V= 35-46°.

Pleochroism:

Slight in shades of pink

and

red.

1-2.

Spectral:

Density:

Not diagnostic.

2.65-2.90.

Cleavage:

None.

Luminescence: Perfect

a=

Biaxial (-), 2

1

direction. Sectile.

1.534-1.556, /3

V=

=

1.586-1.589;

Birefringence:

y=

at

about

Idaho: pale pink. 1.6.

Broken Hill, New South Wales. Australia: and grains, with rhodonite. Scotland; Sweden: red-brown.

0.050.

Not diagnostic.

Luminescence:

In metamorphosed rocks rich in manganese. Kern County. California; Iva, South Carolina; Boise,

Occurrence: 1.596-1.601.

53-62°.

Vague shadow edge on refractometer

Spectral:

1.744-1.764.

Pearly to dull, greasy.

Hardness:

Optics:

y=

0.016-0.020.

Birefringence: Luster:

1.728-1.750;

Finland: brown.

Weak cream white in LW (China) — vari-

ety called agalmatolite.

Occurrence: In schistose metamorphic rocks; also hydrothermal veins with micas, quartz.

in fine crystals

in

Honshu, Japan:

gemmy

material.

Stone Sizes: Faceted gems are always small since the material is extremely scarce and available only as small transparent grains. Large cabochons could be cut from

PYRRHOTITE

756

cleavages and massive material. Collectors should expect to see stones

up

to

about 2 carats.

Hardness:

Comments: Pyroxmangite is a very rare gemstone grains are seldom clean enough to facet. The material resembles rhodonite and bustamite to a certain degree but can be distinguished on the basis of optic sign and birefringence. Faceted gems are hard to cut because of the cleavages, but once completed they are extremely beau;

tiful

and rich

Name:

Originally thought to be manganiferous pyrox-

PYRRHOTITE Fd

Hexagonal; also orthorhombic, mono-

depending on stoichiometry. Crystals

pyramidal, sometimes

tabular, platy,

in clusters (rosettes); usually

mas-

sive or granular.

Colors:

Bronze-yellow to bronze-red or brownish;

tarnishes readily,

Streak:

4.58-4.65.

Density:

Cleavage:

None; sometimes basal parting observed;

fracture subconchoidal to uneven; brittle.

Other

Tests:

heating.

Magnetic, varying

in intensity, lost

on

Decomposed by HC1.

Occurrence: Associated with pyrite and other sulfides throughout the world, often as a magmatic segregation in basic igneous rocks. Occasionally in pegmatites and contact metamorphic rocks, fumaroles, and basalts. Also occurs in meteorites. Sudbury, Ontario, Canada.

*S.

Crystallography: clinic,

3.5-4.5.

in color.

ene, based on studies of the material from South Carolina.

Formula:

Metallic; opaque.

Luster:

becomes

grayish black.

iridescent.

Morro Velho, Brazil. Rumania; Italy; Germany; Norway; Sweden. Potosi Mine, Santa Eulalia, Chihuahua, Mexico. Pennsylvania; Tennessee;

New

York; Maine; Connecticut.

Stone Sizes: Cabochons of almost any size could be cut from the massive material. Such stones are always opaque and metallic and can be attractive.

Name:

From

a

Greek word meaning

reddish.

Q QUARTZ

(= SILICA)

Inclusions:

More than forty types of minerals have been in crystalline quartz. Rock crystal

found as inclusions Formula:

SiCh.

frequently contains cavities or negative crystals with

known as two-phase inclunetwork of cracks creates iridescent effects to produce what is called iris quartz. The minerals noted bubbles, creating what are

Hexagonal (R). Occurs in a wide variety of crystal forms, up to large size; also as crystalline masses, cryptocrystalline, granular, in veins and stringers. Crystallography:

Colors:

Colorless, white, gray (various shades)

sions.

include:

and many

Rut He:

shades of yellow, orange, brown, purple, violet, pink,

red, golden, silvery color.

Sagenite: any type of acicular (needlelike) crystals.

green, and black. Luster:

A

Tourmaline: black, other colors.

Vitreous (crystalline varieties); greasy, waxy

Actinolite: green; fibrous variety

known

as byssolite.

Chlorite: mossy, greenish inclusions.

(cryptocrystalline varieties).

Goethite: yellow and orange wisps, fibers, and crystals.

Hardness:

7.

Hematite: blood-red 2.651 (very constant); in chalcedonies, up to

Density:

platelets.

Chrysocolla: blue-green, finely disseminated.

Dumortierite: blue and violet colors.

2.91.

None

Cleavage:

uneven.

Also: scapolite: hornblende: epidote: anatase; brookite: or indistinct. Fracture conchoidal to

chlorite: micas: ilmenite: calcite; gold: dufrenoysite; oil

Brittle. Cryptocrystalline varieties tough.

droplets.

o

Optics:

Uniaxial

(

+

:

1.544; e

=

1.553 (very constant).

Quartz catseyes have been found. The catseye effect

)

is

0.009 (some chalcedonies 0.004).

Birefringence:

due

The

to inclusions of fine asbestos.

colors are

usually yellowish, brownish, or pale green. This material

always cut into cabochons to bring out the effect. Occurrence: India: Sri Lanka: Fichtelgebirge, Germany. Crocidolite (blue asbestos) may decompose and alter is

Dispersion:

0.013.

None; weak

Pleochroism:

in

amethyst and

citrine; strong

(pink shades) in rose quartz.

Luminescence: ties,

to quartz, retaining the fibrous structure.

further

Varies widely due to traces of impuri-

The

cent colors include browns, greens, white, orange (LW,

als

on Earth;

it

list

is

if

present,

called zebra tigereye.

If

may add

hawk 's-eye. Occurrence: South

a blue

the material

unstained by iron and therefore solid blue,

Quartz is one of the most common mineroccurs in a wide variety of rock types and

numerous

original blue crocidolite,

tone and this

SW). Some material shows phosphorescence. X-rays produce faint blue glow in rose quartz.

geological environments. Localities are too

This can be iron oxides to

yield a dense, siliceous, fibrous material called tigereye.

usually in the cryptocrystalline varieties. Fluores-

Occurrence:

cemented by quartz and stained by

it

is

is

called

Africa.

Crystalline Quartz

Crystalline quartz

to

is

separated here from cryptocrystal-

line or microcrystalline quartz.

but are given in standard mineralogy texts.

757

The

crystalline varieties

QUARTZ

758

ameand milky quartz. quartz are complex and

are those that occur in distinct, visible crystals: thyst,

The

smoky quartz,

color origins

are only

citrine, rose quartz,

in crystalline

now beginning

Amethyst

Amethyst: France.

The deepest

violet or purple quartz.

is

lightest color, a pale lilac

shade,

known

as

The

Rose

oj

color, especially with flashes of red

against a purple background,

to be fully understood.

is

is

referred to as Siberian.

below a temperature of 573°C is known as a-quartz. Between 573° and 870° another silica mineral, tridymite, forms. At 1470°, tridymite undergoes a structural rearrangement, resulting in the appearance of a new silica type called cristobalite, which is isometric. Finally, at 1710°, cristobalite melts to

The term today usually implies a color rather than a locality. The name amethyst is from the Greek amethystos,

an extremely viscous

Inclusions: Prismatic crystals and negative cavities, thumbprint marks, so-called rippled fractures, and twin-

The

stable form of quartz

liquid. If this liquid

a glass forms (silica glass) that has

many

is

chilled quickly,

useful properties

but no regular internal structure. Cristobalite has

some

in

white globules and crystals resembling snowflakes. These

from high temperature. quartz varieties generally occur having been deposited from

result of rapid cooling

The colored, crystalline in

pegmatites and veins,

water solutions over a long period of time. As a result of

many such crystals achieve great and yield enormous pieces of faceting rough. The only color varieties that do not form such large crystals are amethyst and rose quartz.

slow crystal growth, internal perfection

Rock

Crystal:

Used

in

faceted gems, beads, carving,

decorative objects, and lamps.

Nigeria; India; Uruguay; Mexico; Arizona: North Carolina.

ning

no gem significance but appears

types of volcanic glass (see obsidian, page 137) as

form as a

meaning not drunken because the Greeks believed imbibing from an amethyst cup would prevent intoxication. Occurrence: Brazil; Zambia; USSR; Namibia; Australia:

The

material

is

common

and has little intrinsic value, except in very large, flawless pieces. There are many types of mineral inclusions known. Occurrence: Hot Springs, Arkansas; Herkimer. New York; Swiss Alps; Minas Gerais. Brazil; Japan; Madagascar; New South Wales, Australia; Upper Burma; Canada.

lines.

Transparent green quartz

produced by heating

is

cer-

tain types of amethyst.

Amethyst-citrine:

This material, also known as

ametrine, trystine. and so forth, was originally reported

from Rio Grande do Sul, Brazil, but later was shown to occur in Bolivia. Cut gems display both violet and yellow colors, sometimes in a striking zonal pattern, corresponding to rhombohedral growth regions. Heat treatment of both natural and synthetic amethyst can produce similarly colored material, and such stones are indistinguishable from natural ones.

The

Rose Quartz:

The

material

is

color of rose quartz

is

due

to Ti.

nearly always cloudy or translucent,

The

rarely transparent.

color

is

pale pink to deep pink,

mainly used in cabochons, carvings, and decorative objects. Microscopic rutile needles may rarely rose-red.

It is

create a star effect. Occurrence: Maine; South Dakota;

New

York; Brazil; Madagascar; India; Japan; Namibia;

USSR. Milky Quartz: The milkiness is due to myriad tiny and bubbles filled with C0 or water. Vein quartz is often white and frequently contains gold. This quartz is little used in gems, except cabs with milky quartz and yellow gold specks. Occurrence: California; Colorado.

cavities

2

Brown Quartz:

The

variety called

smoky quartz

is

brown in color. Very dark brown material is known as either morion or cairngorm. the latter from the locality in the Cairngorm Mountains, pale beige, tan, brown, or deep

Scotland.

The

radioactivity.

color appears to be caused by natural

Occurrence: Minas Gerais. Brazil; Scotland;

Madagascar; Switzerland; Korea: California; North

A rock made up of tightly packed quartz formed at high temperature and pressure, due to metamorphism. Sometimes it contains small crystals that reflect light, and this material is called aventurine. Usually the included crystals are a green, chrome-rich mica called fuchsite. Other micas that may form aventurine include gray varieties or brown types (from Chile). The density is usually 2.64-2.69. Occurrence: Spain; USSR; Quartzite:

grains,

India: Chile.

Dumortierite Quartz: material tierite,

A

dense, deep blue to violet

made up of crystalline

quartz colored by dumor-

a complex borosilicate.

Carolina.

Cryptocrystalline Quartz

Yellow Quartz: ranges

in

This variety

is

known

as citrine

and

color from pale yellow through yellow-orange

Cryptocrystalline quartz varieties are colored chiefly by

growth environment, including and other elements. They form either as gelatinous masses that slowly dehydrate and crystallize or by deposition from slowly percolating mineral impurities

in the

golden orange, to very dark orange. A deep brown color is produced by heating certain types of amethyst. The name is from the old French citrin meaning yellow. and the color is due to ferric iron. Occurrence: Minas

groundwaters, depositing

Gerais. Brazil; Madagascar.

time. This latter type of deposition results in banding

to rich

oxides of Fe,

Mn,

Ti, Cr, Ni,

silica

over a long period of

QUARTZ that

is

seen

certain types of agate. Deposition within a

in

spherical cavity, such as a gas pocket

volcanic rock, results

in

basalt or other

concentric banding also seen

in

Cryptocrystalline quartz varieties offer a huge diver-

The most generally widespread of these materials is composed of tiny fibers of silica and is known as chalcedony. Names within the of patterns

and

colors.

cryptocrystalline quartz family are generally based colors and patterns.

on

The solid-colored materials are mostly

chalcedony stained by oxides and are referred to as

Banded varieties, or materials with mosslike known as agate.

jaspers.

inclusions, are

Chalcedony: Unstained material often grayish blue, compact form of silica. Occurrence: India; USSR; Iceland; Mexico; California. A purple-colored chalcedony from Arizona has been marketed under the trade name damsonite. The material occurs in veins and blocks up to 1 m thick, with masses over 100 kg recovered. Properties are normal for chalcedony (R.I. = 1.54, S.G. = 2.61), and coloration appears to be the same as that for amethyst.

red, or brownish chalcedony.

The

color

is

due

to iron

Almost any chalcedony can be turned red by

heating in an oven since iron

it

inclusions that look like pictures of scenery, with lakes,

intricate swirls

iron oxide layered with chalcedony, resulting in irides-

cence brought out by cutting and polishing. Shell agate is patterned by is

is

more opaque. Occurrence:

Deep green opaque due

Plasma:

;

more brownish

in

Brazil; Uruguay. to densely

packed

Green or yellowish green chalcedony.

Bloodstone: Also known as heliotrope, consists of dark green plasma with blood-red and orange spots of iron oxides. Occurrence: India; Brazil; Australia; United States.

shell

agate

fragments of the

Banded agate is from Brazil. Uruguay. Madagascar, Mexand the United States. Lace agate is from Mexico, Arizona, and Namibia (blue). Fire agate is from Mexico. ico,

Usually a mass of tiny

Jasper:

by impurities.

The

colors

silica crystals

may be

pigmented

very strong, especially

shades of brown, yellow, red, and green. Jasper occurs worldwide. Orbicular jasper has spherules of banded in a

jasper matrix. Scenic or picture jaspers have

fanciful patterns that

may resemble

scenery, such as

ocean waves, shores, and rolling hills. Occurrence: Oregon; Idaho; Utah; Montana; Wyoming. Chrysocolla

in

Quartz:

A

tough, siliceous material

in silica, to

produce a rich blue, hard material that

takes an excellent polish. Occurrence: Arizona;

New

Mexico; Mexico. Petrified

Wood:

Colorful agate that has replaced

and limbs; the woody structure is preserved in many cases and can be seen with a microscope. The colors may be very bright and strong. Occurrence: Arizona; New Mexico; California; Washington; Oregon; various European countries; many other localities. Dinosaur Bone:

Silicified

lovely brownish color

and

dinosaur bone!

interesting pattern.

It

has a

Occurrence:

Colorado; Wyoming; Utah. Other colors include red,

Banded black and white chalcedony.

Onyx:

and

tree trunks

actinolite crystals.

Prase:

of shells

gastropod Turritella and certain other species. Occurrence: Moss agates are from India. Scotland, and the northwestern United States. Scenic agates are from Yellowstone National Park. Wyoming and Montana.

nated Similar to carnelian, sard

color and

silicified shells in the rock. Turritella

composed mostly

consisting of blue chrysocolla in fine particles dissemi-

Uruguay; Egypt; India.

Sard:

and shrubs. Lace agate is banded with and loops. Fire agate has platy crystals of

shorelines, trees,

contains finely disseminated

compounds that are oxidized by heating. Occurrence:

Brazil;

Banded agates have regular The moss agates have

color layers and bright colors.

agate

Translucent to semiopaque, red, orange-

Cornelian: oxide.

sometimes creating the impression of landscapes,

vegetation, and so forth.

mossy inclusions of mineral oxides. Scenic agates have

in agates.

sity

sions,

159

pink, blue, purple, green, orange, etc.

Sardonyx:

Banded onyx, with red and white

layers.

Stone Sizes: Chrysoprase:

by nickel.

Translucent green chalcedony colored

May resemble

fine jade.

Occurrence: Western

Australia (Yandramindra, Wingelina. Kalgoorlie);

USSR;

Brazil; California.

Flint

and Chert:

Opaque,

dull gray, or whitish chal-

Patterned Chalcedony

Agate: flat

crystal reaches

enormous

size, as illustrated

by

Burmese material

in SI. This is the largest fine Faceted gems of thousands of carats have been cut, such as the 7000 carat stone in SI and the 625 carat star quartz from New Hampshire. Citrines in the thousands of carats are also known. SI has Brazilian stones of 2258, 1 180, 783, 278, 265, and 217 carats, for example, and most large museums have simi-

flawless

crystal ball in the world.

cedony, very compact and hard.

bands,

Rock

the 12.75-inch diameter, 107-pound perfect sphere of

Usually takes the form of colored layers or or concentric. Also mossy or dendritic inclu-

lar baubles.

Smoky

quartz

is

in the

same

size league as citrine, but

QUARTZITE

160

larger stones get very dark

and opaque. SI: 4500 (Califorand 1695 (Brazil), plus others. Rose quartz gems are seldom transparent, especially above 20-30 carats. Large spheres of rose quartz are

quently dyed with aniline dyes to

nia)

quartz gems vary

milky at best.

of decorative stones for

Amethyst

rare in very large, transparent masses.

is

The fine gems at 5/ are exceptional, such as the

1362-carat

and the 202.5-carat stone from North

Brazilian stone

Carolina.

Quartzite and milky quartz are massive varieties available

in large

pieces.

Chalcedony

is

usually nodular, but

masses can be several pounds and many inches Star quartz

in

diameter.

a rarity, but especially noted in rose

is

quartz. SI has a sphere of Brazilian star material weighing 625 carats.

Chrysoprase nodules of 700 and 1470 kilos have been found near Kalgoorlie, Western Australia.

Comments:

Quartz is composed of Si and O, the two most abundant elements in the crust of the Earth. It displays a vast array of colors and shapes (when in crystals), and the cryptocrystalline varieties offer an almost endless spectrum of color and pattern. The basic properties of crystalline

quartz are very constant despite color

Many silica varieties can and dyes

be treated by heating,

irradi-

Chalcedony

is fre-

to alter their color.

many

rich colors.

The

with amethyst the rarest

color, especially in large clean pieces. Cryptocrystalline

varieties are so

Names:

Rock

abundant that they offer a rich selection wear at very modest cost. is from the Greek krystallos, meanGreeks thought it was ice frozen

crystal

ing ice, because the

forever hard by an unnatural frost created by the gods. Amethyst comes from the Greek amethystos, as mentioned. Citrine is in allusion to the color citron (yellow). Chalcedony is an ancient name, perhaps from Chalcedon, a seaport in Asia Minor. Agate is from the Greek achate, the name of a river in southwestern Sicily where the material was found. Onyx is from the Greek word for nail or claw. Sard is from Sardis, the ancient locality reputed to be the origin of the stone. Carnelian is from the Latin carnis (flesh), in allusion to the red color. Plasma is from the Greek for something molded or imitated because it was used for making intaglios. Prase is from the Greek prason, meaning leek, in allusion to the color. Heliotrope is from Greek words helios (sun) and tropein (turn) because, according to Pliny, it gives a red reflection when turned to face the sun while immersed in water. Flint and chert are of uncertain origin.

variation.

ation,

in scarcity,

QUARTZITE

see: Quartz.

R

REALGAR

Comments:

Formula:

AsS.

world.

Monoclinic. Crystals prismatic,

Crystallography: ated;

It

is

impossible to wear.

stri-

extremely rare

compact, powdery.

Colors:

Dark

Streak:

Orange-yellow.

Luster:

Resinous to greasy.

Hardness:

is very seldom transparent, although widespread in occurrence throughout the is extremely soft and fragile, difficult to cut, and

Realgar

the mineral

and very

lovely.

Name:

From

Biaxial

is

the Arabic Rahj-al-ghar,

meaningpouYter

of the mine.

RHODIZITE

3.56.

CsAUBe^BuOaslOH)^

Crystallography:

Good

1

Birefringence:

Dispersion:

2.684;

y =

Colors:

2.704.

Isometric. Crystals dodecahedral or

to 2

cm

size;

massive.

Colorless, white, yellowish white, yellow, gray,

rose red.

Luster:

0.166.

Vitreous to adamantine.

Hardness:

Strong.

Density:

Pleochroism:

up

tetrahedral,

direction. Fracture conchoidal. Sectile.

a = 2.538; p = (~),2V= 40°.

8.5.

3.44.

Strong: colorless to pale yellow.

Cleavage: Spectral:

cut only for collectors but

1.5-2.

Cleavage:

Optics:

It is

cut form. Stones are a fine red color

red, orange-red.

Formula: Density:

in

Difficult. Fracture conchoidal. Brittle.

Not diagnostic. Optics:

Luminescence:

None.

May decompose on strong expo-

Isotropic; TV

=

1.694.

Anomalously birefringent (may not be

truly isotropic).

sure to light.

Dispersion:

Occurrence:

Spectral:

and silver. Getchell Mine, Nevada; Manhattan, Nevada; Mercur,

its,

especially with ores of lead

Not diagnostic.

Luminescence:

Utah; Boron, California.

ish

Rumania; Czechoslovakia; Germany; Switzerland; Japan. King County, Washington: fine crystals, up to 2 inches long, some gemmy.

Weak yellowish glow in SW; strong green-

and yellowish, with phosphorescence,

Occurrence:

in X-rays.

A pegmatite mineral with few noteworthy

localities.

Antandrokomhy, Madagascar (and other localities in that country): yellowish and greenish crystals, some gemmy. Near Mursinsk, USSR: rose red color.

Occasional fragments of Washington cryscut gems to about 3 carats.

Stone Sizes: tals will

0.018.

Low-temperature hydrothermal vein depos-

767

RHODOCHROSITE

762

Madagascar material in fragments clean up to about 3 carats.

Stone Sizes:

enough

to cut has provided stones

have concentric structures that display interesting bullseyes

SI: 0.5 (Madagascar).

Comments:

Rhodizite

is

quite a rare mineral, and only

Madagascar has produced gem-quality crystals. Faceted gems are extremely rare and usually pale in color. The mineral is rather hard and stones would be excellent for jewelry, especially since there is no cleavage.

From

Name: it

Greek

the

San Luis, Catamarca Province, Argentina: massive and banded material, also stalactites up to 4 feet long! These

for to

be rose-colored because

imparts a red color to the flame of a blowpipe.

when

cross-sectioned.

Some

Series to Siderite (with Fe substi-

Ca

tution); series to Calcite (with

MnCO, +

Formula:

Massive material from Argentina occurs and has been carved, cut into beads, boxes, cabochons, and useful objects. Faceted, translucent pink material cuts stones up to about 20 carats. South African rhodochrosite is rich rose red in color and in

large pieces

9.5 carats.

gems are in the gems of 20.8, 15.2, Colorado pink gems are perhaps the

Hexagonal

(R). Crystals

rhombs and

elongated scalenohedra; massive, compact, stalactic. Pale pink, rose red, deep pink, orangish red,

Colors:

DG:

Vitreous to pearly.

5.95 (red. South Africa).

PC: 59.65

NMC:

(red oval. South Africa).

18.05 (red oval, South Africa).

lectors that

Hardness:

good

3.5-4.

3.4-3.6 (pure

Density:

=

15 carats

Comments: Rhodochrosite is very rare in faceted form. The specimens are in such demand among mineral col-

yellowish, gray, tan, brown.

Luster:

largest cut

and have been cut up to about Most stones are under 5 carats.

flawless.

Crystallography:

The

60-carat range. SI has South African

loveliest of all

Fe, Ca.

trans-

Stone Sizes:

and

substitution).

is

Peru: facetable, pink crystals.

rare in facetable crystals.

RHODOCHROSITE

Argentinian material

lucent and has been faceted.

would be an outrage to most to cut up a Hotazel gems of large size have been availa-

it

crystal.

and expenColorado pink rhodochrosite in clean gems is also expensive, and anything over 2-4 carats is considered ble, but larger clean stones are very scarce

3.7).

sive.

Perfect rhombohedral. Brittle.

Cleavage: Optics:

o

=

=

1.786-1.840; e

very large. Argentinian material 1.578-1.695.

Uniaxial (— ).

Ca

in

formula reduces indices and density; Fe and

Zn

rial

increase them. This also applies to the birefringence. Single crystals varies

up

may be zoned and

to 0.01 within a

space of one inch

in

some

Pleochroism:

0.201-0.220. Faint in

Band

at

deep red

generally quite small. Peruvian stones resem-

is

from Colorado

Name:

From

Greek

the

also.

for rose-colored, in allusion to

Tests:

Luminescence:

RHODOLITE

See: Garnet.

RHODONITE

Pyroxene Group.

varieties.

5510 and 4100, plus vague

lines at

5350 and 5650.

Other

translucent at best

the color.

Birefringence:

Spectral:

but

ble those

the refractive index

material.

is

and much less costly, but few gems have appeared on the market. Mexican gem material resembles Colorado mate-

MnSiOi (+ Ca

Formula: Effervesces in

Fluoresces

warm

medium

igan), also dull red to violet in

pink

SW

in

LW (Mich-

(Argentina and

maximum

of 20%).

Triclinic. Crystals tabular; massive,

Crystallography:

acids.

to

cleavable. granular.

Colors:

Rose red, pink, brownish red; often veined by

Mn

Colorado).

black

Occurrence: A gangue mineral in hydrothermal veins and a secondary mineral in ore deposits. Colorado: spectacular crystals, pink to deep red, small to 3 inches on an edge. The world's finest rhodochrosite comes from A Ima, Colorado: some isfacetable (red) and pink faceting rough also exits from other localities. Butte, Montana: crystal groups (non-gem). Magdalena, Mexico: sometimes in cuttable pieces. Hotazel, South Africa: facetable, deep reddish crystals.

Luster:

oxides.

Vitreous; massive material dull.

Hardness: Density: Cleavage:

5.5-6.5.

3.57-3.76 (massive); 3.67 in crystals. Perfect

tle (crystals);

Optics: in

tough

Biaxial

(

1

direction. Fracture conchoidal. Britif

+ ),

compact.

2V= 63-76°.

Shadow edge

massive varieties. See following table:

at 1.73

RUTILE Q

P

Y

Birefringence

Density

2V

1.726 1.720

1.731

1.725

1.739 1.733

0.013 0.013

3.57 3.62

64° 75°

1.723-1.726

1.728-1.730 1.716-1.741

1.735-1.737 1.723-1.752

0.011-0.013 0.01 1-0.014

3.68-3.70 3.57-3.76

74° 63-76°

Honshu, Japan Pa/sberg,

Broken

Sweden

New

Hill.

South Wales,

Australia

1711-1 .738

General

Weak, but may be

Pleochroism:

distinct: yellowish red/

Broad band at 5480, strong narrow line weak band at 4550. May also see lines

5030, diffuse

at

Name:

From

RICOL1TE

Luminescence: Medium dull red in deep red in LW (Langban, Sweden).

Greek rhodos,

the

in allusion to

the color.

at

4120 and 4080.

See: Serpentine.

SW (Hungary), dull

ROCK CRYSTAL

In manganese-bearing ore bodies or in

Occurrence:

rhodonite. However, the distinctly lower refractive indi-

ces of bustamite should prove diagnostic.

pinkish red/pale yellowish red. Spectral:

163

ROSOLITE

See: Quartz.

See: Garnet.

their vicinity.

New Jersey.

Montana; Franklin,

California; Colorado;

ROYAL AZEL

See: Sugilite.

Cornwall, England; Mexico; South Africa.

USSR: massive pink and rose colored material, very fine and rich (Sverdlovsk). Australia: fine transparent crystals and massive material at Broken Hill, New South Wales. Vermland, Sweden: good color gem material. Honshu, Japan: facetable material. Daghazeta, Tanzania: fine-quality massive material. Bella Koola, British Columbia. Canada: fine pink, with

black patterns;

localities

available in large pieces, often with attractive black

veining of manganese oxides. This material is cut into cabochons, goblets, vases, and other decorative objects, including figurines and boxes. Faceted gems are extremely rare and are derived primarily from crystals found in Australia and Japan. The maximum size of such stones is in the 2-3 carat range, but a few larger stones may exist.

Comments:

Rhodonite

is

tive material,

ranging

color from pink to a fine rose-

red.

in

a popular

and useful decora-

Faceted gems have an intense and beautiful color

but are delicate due to perfect cleavage. This cleavage

is

extremely easy to develop, and rhodonite has the reputation of being

Most

one of the most

available rough

is

RUBELLITE

RUBY

See:

difficult of all

gems to facet.

very small. British Columbia

produces fine rhodonite similar in appearance to the Russian material. The best of B.C. rhodonite, however, is deep rose-pink and translucent. The grains of gemmy rhodonite embedded in galena (lead sulfide) at Broken Hill, New South Wales, Australia, are distinctive. Rhodonite occurs at this locality with pyroxmangite, a related mineral, and also with bustamite, (Ca,Mn)Si 2 Oh, which occurs in crystals up to 100 cm long! Cuttable bustamite does occur and may exist in many collections, labeled as

See: Sugilite

See: Tourmaline.

Corundum.

RUTILE TiO> + Nb, Ta, Fe.

Formula:

translucent.

Massive rhodonite from various

Stone Sizes: is

some

ROYAL LAVULITE

Crystallography: striated, well

Tetragonal. Crystals prismatic, vertically

developed, often twinned into a series of

contact twins with up to eight individuals, sometimes looping to form a complete circle! Also massive; granular. Black, deep red, brownish red. Greenish

Colors:

present), also bluish

and

violet.

A

variety rich in

(if

Nb

Cr

is

deep green. Pale brown to yellowish; grayish or greenish

Streak: black.

Luster:

Metallic to adamantine.

Hardness: Density:

Ta =

6-6.5.

4.23; ferroan variety

=

4.2-4.4; with

Nb and

4.2-5.6.

Cleavage:

uneven.

o

Optics:

Uniaxial

Distinct

1

direction. Fracture conchoidal to

Brittle.

(

+

=

2.62; e

=

2.90.

).

Sometimes anomalously Birefringence:

Dispersion:

0.287.

0.280.

biaxial.

RUTILE

164

Pleochroism:

Distinct: shades of red,

brown, yellow,

green.

Magnet Cove, Arkansas:

Spectral:

Not diagnostic.

Luminescence:

huge rough

crystals.

Occurrence:

Stone Sizes:

Large crystals often have transparent areas can provide stones' for faceting. However, a cut rutile above 2-3 carats is so dark it looks opaque, effectively limiting the size of cut gems. that

None.

Commonly

seen as needles in quartz and in agate (sagenite). Also present as fibers in corundum, creating stars in these gems. Present as needle inclusions in a wide variety of gem

(nitillated quartz)

DG:

3.70.

Comments: finished

minerals.

Also occurs as a high-temperature mineral, in gneiss and schist, also in Alpine-type veins; found in igneous

metamorphosed rocks, includand as detrital grains. North Carolina; South Dakota; California.

rocks, pegmatites, regionally

ing crystalline limestones, Virginia;

USSR;

in

Brazil: large, fine crystals.

gems

Rutile

gem

is

is

often cut as a curiosity, but the

disappointing because

are usually

deep red

in color,

it is

so dark.

but the color

The is

so

cannot be easily seen in stones larger than 1 carat. Cabochons of rutile might show reddish reflections in cracks and along imperfections. Swiss rutile seems a bit more transparent than material from other intense that

it

localities.

Switzerland; France.

Graves Mountain, Georgia: in quartz veins, fine up to several pounds in size.

crystals,

Name: color.

From

the Latin rutilus (red), in allusion to the

s

SALITE

since black stones are not terribly attractive.

See: Diopside.

a stone

SAMARSKITE Formula:

See

also: Euxenite, Fergusonite.

Name:

(Y,Ce,U,Ca,Pb)(Nb,Ta,Ti,Sn) 2 06.

massive, compact.

Colors:

Velvety black, yellowish brown on exterior.

Streak:

Black to reddish brown.

SANIDINE

See: Feldspar.

SAPPHIRE

See:

Formula:

submetallic.

of

Hardness: Density:

— usually

near upper end

N=

20

(+ Fe).

Complex

substitution

= (Mg,Al)K(Al,Si) o; = (Mg,AI) Al,Si) triclinic. 6

K(

Monoclinic or

h

2

2l) ;

triclinc; crystals tabu-

lar; usually granular or as disseminated grains.

Indistinct. Fracture conchoidal. Brittle.

Isotropic;

O

polytypes: Sapphirine-2M

Crystallography:

Cleavage:

s

monoclinic. Sapphirine-lTc

of range.

Optics:

Mg,<,AL„Sii

Mg/Al/Si with charge balancing.

Two

5-6.

5.25-5.69 (variable)

Corundum.

SAPPHIRINE

Dull after alteration; resinous; vitreous,

Luster:

honor of Colonel Samarski, a Russian min-

In

ing official.

Monoclinic. Crystals rough, tabular;

Crystallography:

Sometimes

faceted in the nature of jet or marcasite.

is

Pale blue, bluish gray, greenish gray, green;

Colors: 2.20 (variable).

depth of blue color varies with Fe. Also

Isotropic nature caused by metamictization.

(rarely) purplish

pink.

None.

Pleochroism:

Vitreous.

Luster:

Luminescence:

None. Hardness:

Occurrence: A widespread pegmatite mineral. North Carolina; Colorado. USSR; Norway; Madagascar; Zaire; Japan; Minas Gerais, Brazil; Madras, India.

Density:

Optics:

at

Large cabochons can be cut from masses various localities. This material is essentially

a=

1.714-1.716;

Birefringence:

Samarskite

which lustrous black

to

times cut as curiosities. is

Indistinct; fracture

is

not intended for wear.

It is

1.719-1.721;

y=

1.720-1.723.

0.006.

X

brownish cabochons are someis

=

to subconchoidal.

== pinkish buff; yellowish: Pleochroism: Distinct: pale smoky brown; colorless; Y = sky blue; sapphire

a very heavy material from

The material

/J

uneven

Biaxial (— ).

opaque.

Comments:

3.4-3.5.

Cleavage:

Stone Sizes:

found

7.5.

blue; greenish blue;

rather brittle and

rarely seen or displayed

Spectral:

765

Z=

dark sky blue; sapphire blue.

Not diagnostic.

SAFICOLITE

766

None

Luminescence: Occurrence:

Comments:

reported.

In mineral veins or cavities in eruptive

igneous rocks.

Keweenaw

Utah;

Milford,

Peninsula, Michigan; Lake

Tiny gems have been faceted from crystals only known locality at Monte Somma. These stones are all very small (under 1-2 carats) and are extremely rare.

found

at the

Superior, Minnesota.

Name:

Canada; Scotland; England; Sweden; Czechoslovakia; Japan; South Africa; Greenland: Madagascar; Italy; Sri

allusion to the color.

Lanka.

SARD

Stone Sizes:

Facetable sapphirine

even though the material occurs

GIA

in

is

noted a very unusual purplish-pink stone of 1 .54 cts, mica "book" (phlogopite), from

Lanka;

R.I.

0.006; S.G.

=

=

1.701-1.707;

The

3.51.

f)

=

1.705; birefringence

Name:

exist but

is

biaxial.

Other

have been misidentified.

SATELITE

and stone,

in

See: Serpentine.

SATIN SPAR

See:

Gypsum.

SCAPOLITE = WERNERITE (

Marialite:

Crystallography: large

(Ca,Na) 4 Al 3 (Al,Si) 3 Si6024.

is

intermediate.

3Na(AlSi 3 )O s •

CaC0

•

NaCl.

3.

Tetragonal; crystals prismatic, often

and coarse; massive, granular, cleavages.

Colors:

Colorless, white, bluish gray, pale greenish yel-

low, pink, violet,

Tetragonal. Crystals equant, grains.

Solid-solution series:

)

Marialite to Meionite. Mizzonite

Formulas:

SARCOLITE

Crystallography:

for flesh

See: Quartz.

Meionite: 3Ca(Al 2 Si2 )0 8

In allusion to the (sapphire blue) color.

Formula:

Greek words

=

refractive indices of sapphirine

are close to idocrase, but the former

such gems

the

exceedingly rare,

transparent grains.

oval, with an included Sri

From

brown, orangy-brown, golden yellow,

orangy-yellow.

Colors:

Reddish, rose red, reddish white.

Luster:

Vitreous.

Vitreous; resinous; pearly on cleavages.

Luster:

Hardness:

Hardness:

6.

6.

2.50-2.78; varies with composition.

Density: Density:

2.92.

None. Fracture conchoidal. Very

Cleavage: Optics:

Uniaxial

o (

=

1.604-1.640; e

=

Distinct 2 directions. Fracture uneven to

Cleavage: brittle.

subconchoidal; Dispersion:

+ ).

0.017.

Pleochroism: Birefringence:

brittle.

1.615-1.657.

Pink and

violet stones:

dark blue/lavender

0.011-0.017. blue; colorless/violet.

Occurrence: this

is

In volcanic rock at Mt. Vesuvius, Italy

the only locality

Marialite

Umba Umba Umba Umba

Mozambique

River, River,

River, River,

Tanzania Tanzania Tanzania Tanzania

Rio Pardo, Brazil

Burma Burma Burma Burma Burma

yellow yellow-gold violet

yellow very pale yellow golden yellow colorless pink light yellow pale pink

(catseye) Sri Lanka (catseye] Kenya (catseye)

gray

Madagascar

(colorless)

Meionite

Group

violet

1.546-1.550 1.568 1.562-1.567 1.539-1.540 1.553 1.579 1.570-1.574 1.560 1.558 1.587 1.549 1.560

1

colorless to pale

Birefringence

Density

.540-1 .541 1.548

0004-0008

2.50-2.62 2.70 2.66-2.67 2.59 2.63 2.74 2.68-2.70

1.545 1.554 1.540 1.544 1.553 1

1.568-1.571 1.590-1.600

e

1.543-1.548 1.531-1.534 1.539 1.553 1.549-1.552 1.544

1.583

brown

—

stones:

Properties

Color

Locality

and pale yellow

Colorless

yellow/yellow.

Table of Scapolite

Entre Rios,

—

(Monte Somma).

.57

1.550-1.552 1.556-1.562

0.020 0.019 0.007 0.014 0.026 0.021

0.016 0.013 0.033 0.009 0.016 0.030

— — — 2.63 2.63

—

—

2.73

0.018-0.020 0.024-0.037

2.78

—

SCHEELITE

6

04 i

02 R.I.

1

00

59

167

Ontario. Canada: light yellow, pink and green material yielding tiny cut gems.

Stone Sizes: Burmese white and yellow gems have been found in large sizes. Pink Burmese step-cut gems to 70

finest

been reported. Catseyes are usually under 10 ones are known. Tanzania produces the golden yellow scapolite known in commercial quan-

tities.

Pink gems are extremely rare, violet stones very

carats have

carats, but larger 1

58 =

R.I. 1

(o

+

e)/2

57

rare in sizes over 5 carats. Brazilian yellow scapolite

cuttable up to about 30 carats but 1

1

56

is

is

usually flawed (long

thin tubes) at this size.

ROM:

55

28.4, 57.6 (yellow, Brazil); 7.91 (pink,

Burma);

65.63 (colorless, Burma); 18.8 (gray, catseye); and 18.3 (pink, catseye).

1-54

Burma); 29.9, 19.7 (catseye, colorless, Burma); 29 (yellow, Brazil); 17.3 (catseye, pink, Sri Lanka):

SI: 288 (colorless, 1-53

— Mar alite-*10

lizzon

3 pyre i

30

20

40

% Me

50

60

90

80

70

Burma);

12.3 (pink,

>nite-»-

DG:

100

103.4, 52.2 (yellow-orange, Tanzania).

3.34 (blue catseye, Burma); 21.25 (white catseye,

India).

= Ca: (Ca + Na)

Refractive index and birefringence [6) as related to chemical composition in the scapolite group. Chemistry is expressed as (molecular) percent meionite, which reflects the ratio Ca/(Ca + Na) in the formula. Refractive index is plotted as a mean index = (o + e)/2.

Adapted from W. A. Deer, R. A. Howie, and J. Zussman, 1962, The Rock Forming Minerals, vol. 4 (New York: Wiley), p. 329.

PC:

14.83 (violet, Tanzania

— largest known of this color);

52.92 (green-brown catseye).

Catseye scapolites from Burma are very an unusually sharp eye, and occur in vari-

Comments: rare, possess

ous colors. Cabochons from opaque Quebec and Ontario material are very lovely and often fluoresce brightly. The Tanzanian golden scapolite is much darker in tone than the Brazilian material, and over, there

Spectral: at

Pink and violet stones show bands

6630 and 6520 due to

in the

red

Cr. Strong absorption in the

yellow part of the spectrum.

to orange in

LW (U

SW;

in SW, inert in LW. Quebec: massive material fluoresces

violet stones

=

pink

in

LW

(+ phospho-

rescence).

Some

The

extremely rare

in sizes

to

much cleaner. Moremake jewelry promo-

pink-purple Tanzanian material

is

over about 5 carats. Most gems of

color are in the 1-2 carat range. Faceted Burmese

Name: spectrum), also pink

Tanzania: strong yellow in both LW,

yellow faceted gems fluoresce

orange

also

scapolites are also rarely found in the marketplace.

Luminescence:

Burma: yellow inSW.

tion feasible.

this

is

enough available

is

lilac in

SW, strong

Scapolite from the Greek skapos (shaft) because stumpy nature of its prismatic crystals. Marialite is named after Maria Rosa, wife of G. vom Rath. German mineralogist. Meionite is from Greek meion (less), because its pyramidal form is smaller than that of idocrase from Vesuvius, which it resembles. Mizzonite is also from the Greek meizon (greater) because the axial ratio is larger of the

than that of meionite.

in X-rays.

Occurrence: In contact zones; regionally metamorphosed rocks; altered basic igneous rocks. Madagascar: yellow, facetable crystals. Espirito Santo, Brazil: pale yellow crystals, sometimes large, facetable.

Burma: white,

SCHEELITE

Crystallography:

yellow, pink to violet,

all

+ Mo.

Tetragonal. Crystals octahedral shaped,

cuttable; also

Colors:

Kenya: brownish catseyes.

ish,

finest transparent

Colorless, white, gray, yellowish white, brown-

orange-yellow, greenish, violet, reddish.

golden yellow to Vitreous to adamantine.

orangy-yellow material, sometimes very pale to near

Luster:

and pink (rare) cuttable crystals. Quebec, Canada: lemon yellow, opaque scapolite, some

Hardness:

with silky

Density:

colorless; also violetish

luster.

4

tabular; massive, granular.

bluish, pinkish, white catseyes.

Dodoma, Tanzania:

CaW0

Formula:

4.5-5. 5.9-6.3.

SCHEFFERITE

168

Cleavage:

Distinct

direction. Fracture subconchoidal

1

o=

Optics:

Uniaxial

(

1.918-1 .920; e

=

1

Name:

Birefringence:

0.016.

the existence of tungsten in scheelite in

1781.

"didymium"

lines in the yellow

and

green, especially 5840.

Luminescence: Brilliant bluish white LW, or dull yellow (Sri Lanka).

in

SW;

inert in

Occurrence: In contact metamorphic deposits; hydrothermal veins; pegmatites; placer deposits. Connecticut; South Dakota; Nevada; New Mexico. Finland; Switzerland; France; England; Italy; Czechoslovakia; Germany; Japan; Australia; Canada; Bolivia;

SCHEFFERITE

SCHORL

See: Tourmaline.

SCHORLOMITE SCOLECITE

See: Garnet

See: Natrolite.

SCORODITE

Series to Mansfieldite:

gemmy

California: colorless

•

2

•

2

Orthorhombic. Crystals pyramidal,

Crystallography:

tab-

crystals.

Utah, near Milford: orange crystals, octahedral,

some

ular,

prismatic; massive, crusts.

Colors:

tips.

Korea: white, grayish

Al As0 4 2H 0.

FeAs0 4 2H 0.

Formula:

Peru.

See: Diopside.

Arizona: brown, large crystals, sometimes gemmy.

with clear

Smaller, clean

After Karl Wilhelm Scheele, Swedish chemist,

who proved

0.038.

Faint

Spectral:

diamond, and properly cut gems and brilliance. Crystals in muse-

fire

ums could yield stones over 100 carats. gems are available in the marketplace.

.934- 1 .937.

+ )•

Dispersion:

sion approaches that of

can have tremendous

to uneven. Brittle.

sometimes very

crystals;

large,

Pale grayish green, yellowish

brown

to

brown,

colorless, bluish green, blue, violet.

cuttable in portions. Sri

Lanka: colorless,

Stone Sizes: localities

Crystals from Korea, Arizona, and other

may be

very large (4 inches on an edge) and are

cuttable in sections. California ats;

Luster:

(gemmy).

gray, yellow

gems may reach 70

Mexican and Arizona stones

are usually

up

to

Vitreous to resinous.

Hardness: Density:

3.5-4.

3.28-3.29.

car-

about

Cleavage: Optics:

Imperfect. Fracture subconchoidal. Brittle. Biaxial

P

Y

Birefringence

2V

1.795 1.742 1.744 1.796

1.814 1.765 1.768 1.816

0.030 0.027 0.027

75° 60° 40° 75°

Properties of Scorodite from Various Localities

Durango, Mexico Idaho

1.784

Oregon Tsumeb, Namibia

1.741

1738 1.785

Mexican stone over 100 carats

has been cut. Utah crystals rarely cut stones over 7 carats. Crystals

from Korea up to 13 inches have been

found, but none of these has been cuttable. SI: 37, 18.7,

and 15.8

PC:

17.58 (yellow, Mexico); 12.20 (Sri Lanka).

DG:

8.70

(Cohen Mine, Nevada). (intense orange kite step-cut,

Territory,

Comments:

Emerald Lake,

Canada).

Large scheelites are very rare but are

among

The

disper-

the most beautiful of

all

line at 4500,

broad absorption

in the

Occurrence:

A

None. Soluble

in

HC1.

secondary mineral resulting from the

oxidation of arsenious ores.

ROM: 14.0 (colorless, California). AMNH: 20.65 (near Bishop, California).

Yukon

One

green (Tsumeb).

Luminescence:

(colorless, California); 12.4 (golden

yellow, Mexico).

NMC: 8.55

Spectral:

0.031

Intense: purplish/bluish (Tsumeb).

Pleochroism: 10 carats, but an orange

+ ), variable 2 V.

(

the collector gems.

Utah; South Dakota; California; Washington; Idaho: Nevada; Wyoming. Ontario. Canada; Japan; England. Durango. Mexico: fine blue crystals. Ouro Preto, Minas Gerais. Brazil: good crystals, some

gemmy. Tsumeb, Namibia: pleochroic blue long, some gemmy.

crystals, to

25

mm

SERANDITE Stone Sizes:

Cut gems are always small, mostly from The maximum to expect is about 5 carats but even this would be very large for the species.

Name:

Tsumeb

gist,

SI: 2.6 (purplish, Namibia).

SENARMONTITE

material.

Gems of scorodite are extremely rare

Comments: ally

Tsumeb), but cut stones have a

intense pleochroism.

Too soft

to wear, the stone

for collectors of the rare

and unusual.

Name:

for garliclike

rial

From

Greek

the

(

usu-

lovely color is

suited

because the mate-

when

After the Italian mining engineer and mineralo-

Quintino

heated.

cm on

edge; massive.

Colors:

Colorless to grayish white.

Luster:

Resinous. 2-2.5.

See: Lazulite.

Density:

5.5.

Traces. Fracture uneven. Very brittle.

Gypsum.

See:

Optics:

Isotropic;

Luminescence:

SELLAITE

MgF

Formula:

Isometric. Crystals octahedral, up to

Crystallography:

Cleavage:

SELENITE

Isomorphous with Valentinite.

Sb 2 Oi.

Formula:

Hardness:

SCORZALITE

Sella.

and 3

emits the typical garlic odor of arsenic

169

N = 2.087.

None.

Not diagnostic.

Spectral: 2.

Crystallography:

Tetragonal; crystals prismatic, acicular,

A secondary mineral formed by the alter-

Occurrence:

ation of stibnite (SbA).

fibrous aggregates.

Inyo County, California: South Dakota. Colors: Luster:

Colorless, white.

Quebec, Canada: Algeria: France: Germany: Sardinia:

Vitreous.

Italy.

Hardness:

Stone Sizes: There are reports of very tiny gems having been cut from transparent crystal fragments. Stones up

5-5.5.

Density:

3.15.

to 1-2 carats

Poorly observed although literature indicates

Cleavage:

perfect in 2 directions. Fracture conchoidal; brittle.

o

Optics:

Uniaxial

(

=

=

1.378; e

1.390.

+ ).

seem

Comments:

Senarmontite is a rare mineral, restricted occurrence to the presence of antimony sulfide ores. It is much too soft to wear, and the colors are usually nondescript. However, a faceted senarmontite in any size in

would be a great Birefringence:

Name: None.

After Henri de Senarmont, professor of miner-

alogy at the School of Mines

None

Luminescence:

reported.

occurs

Sellaite

SERANDITE

a wide variety of geological

in

environments.

Na(Mn,Ca) 2 Si 3

Formula:

Vesuvius, Italy: in volcanic fumaroles.

Crystallography:

ance, stubby, well formed.

Italy:

in

evaporite beds.

France: in veins.

USSR:

in

Bahia, Brazil:

in a soda-granite.

gemmy crystals in a meta-

morphic magnesite deposit. Stone Sizes:

The

(OH).

Triclinic. Crystals prismatic in

Colors:

Rose red, pinkish, salmon

Luster:

Vitreous, pearly on cleavage.

Hardness: Density:

Brazilian sellaite

is

appear-

red.

cm

4.5-5. 3.32.

the world's only

extant cuttable material, and the largest crystals found

thus far are only 5

8

pegmatites.

Oslo Region, Norway: cavities

Brumado Mine,

who first described

Series to Pectolite.

Harz Mountains, Germany: Nertschin,

in Paris,

the species.

None.

Occurrence:

rarity.

0.012.

Pleochroism: Spectral:

possible.

long with small transparent areas.

Thus, gems of only a few carats have or could be produced. This is an exceedingly rare gemstone, both in occurrence and number of cut stones.

Cleavage: Optics: Biaxial

Perfect

a =

1.660;

(+),2V =

Birefringence:

1

direction. Fracture uneven. Brittle. fi

35°.

0.028.

=

1.664;

y =

1.688.

SERPENTINE

170

Not diagnostic.

Spectral:

Luminescence:

Occurrence: Serpentine forms due to the alteration of basic and ultrabasic rocks. In some instances it may be mistaken for nephrite jade. Bowenite (a translucent green or blue-green variety of

None.

Occurrence: In nepheline syenite rocks at Mt. Ste. Hilaire, Quebec, Canada. Also known from Los Islands, Guinea.

antigorite).

New

Zealand: dark bluish green. S.G. 2.67. Delaware River. Pennsylvania: dark green.

Cut serandite over 2-3 carats is very rare. of any size are very rare. Cutting material comes only from Quebec, and even large crystals seldom have facetable areas. Stone Sizes:

USNM:2+ PC: 5+

NMC:

China:

Transvaal,

(Quebec).

in

green shades.

apple green color.

Rock Springs. Maryland: best-known locality; may contain Crand be deep green in color; R.F (mean) 1.56, S.G.

Comments: This essentially is another one-locality mineral, where very small gems have been cut from an occasional crystal fragment that

is

2.6-2.62, hardness 4.5.

not always even

Lizardite

transparent.

M. Serand, West African mineral

J.

South Africa: banded

Williamsite (a very translucent variety of antigorite):

(flawed).

For

Island: dark green.

light yellowish green.

Afghanistan: green.

18.65, 2.8 (translucent).

Name:

Rhode

Smithfield,

gems

In fact, cut

Kashmir, India: Scotland: gray, green, S.G. 2.51. Lizard Peninsula, Cornwall, England: veined various col-

collector.

ors; S.G. 2.45.

A

SERPENTINE Serpentine

is

South Africa: Austria: Anglesey. Wales. Ireland: mixture of serpentine and carbonates, locally known as Connemara marble; mean R.I. 1.56, S.G.

group of minerals. a group of four species with the same

composition but different properties: antigorite, chrysotile, clinochrysotile, and lizardite. All may form rocks that are cut

Mg

Formula:

2.48-2.77; absorbtion line at 4650.

Antigorite; Faceted

and polished. 1

Si 2

Crystallography:

040H) + 4

gem found

in

material from Pakistan,

yellowish-green, nearly transparent; indices 1.559-1.561, Ni.

birefringence 0.001-0.002.

Monoclinic. Usually flaky or masses

Verd Antique: a green serpentine veined with calciteand in Greece; Italy; Egypt; Vermont.

other minerals. Found

of fibers, never in crystals; fibers usually too small for

good optical readings.

Stone Sizes:

White, yellowish, shades of green, yellowish green, brownish green, bluish white to bluish green, brown-

Serpentine

is

always massive, and usually

Colors:

cut as beads, cabochons, or carved into various useful

ish red.

and decorative objects. Occasionally, it is translucent enough to be faceted (especially williamsite), and such gems are indeed interesting and quite lovely.

Luster:

Resinous; greasy; pearly; waxy; earthy.

Hardness:

2.5;

Comments:

bowenite, 4-6.

Bowenite

is

usually blue-green, yellow-green,

or dark green and translucent; Density:

Variable. 2.44-2.62

is

gem

range; bowenite,

handles, and so forth, and

2.58-2.62.

Cleavage: Spectral:

it is

used for carving, knife

in jewelry.

Williamsite con-

and patches (magnesium hydroxide). Ricolite is a banded serpentine from Rico, New Mexico. Satelite is a serpentine pseudomorph after asbestiform tremolite from Maryland and California, grayish to greenish blue. Pseudophite or styrian jade is from Austria and is an tains dark octahedral crystals of chromite,

Perfect

1

of white brucite

direction. Fibrous.

Bowenite gives bands

at

4920 and 4640-not

diagnostic.

Luminescence:

Williamsite

may glow weak whitish green

inLW.

aluminous serpentine, with hardness

Antigorite

Optics a

1.560 1.566 571 0.014 1

Birefringence Density

Hardness "Bowenite a variety

Chrysotile

Clinochrysotile

1.532-1.549

1.569

—

—

1

545-1 556 0.013

261

2.55

2.5-3.5 a

2.5

of antigorite.

1

570

0.001 2.53

—

has S.G 2 58-2.62 hardness 4-6

Lizardite

1

538-1 554

1

546-1 .560

— 008

255 2.5

2.5, refractive

index

SIDERITE 1.57, density 2.69. Chrysolite,

known

and

as asbestos

is

in

fibrous form,

widely used

in

is

best

industry for

its

tinct species.

The formula

of plancheite

171

is:

CustSLtOuMOH)* jtH 20. •

physical properties.

Names: in

Serpentine from the serpentlike markings seen

a serpentine marble; chrysotile

chrysos (golden) and

is

from the Greek

tilos (fibrous), aptly

SHORT1TE Na Ca

Formula:

2

2

(CO,),.

describing the

properties of this mineral. Antigorite and lizardite are

Crystallography:

named

to

after the type localities, Antigorio Valley, Pied-

maximum

Orthorhombic. Crystals wedge-shaped,

size of 155

mm.

and Lizard, Cornwall, England. Bowenite is Bowen, who studied material from Rhode

Colors:

Colorless to pale yellow.

Island (though he misidentified the material as neph-

Luster:

Vitreous.

mont, after

rite).

Italy,

G.

T.

Williamsite

found

is

named after L. W.

Williams,

who first

Hardness:

3.

it.

Density:

SHATTUCKITE Cu

Formula:

5

Cleavage:

(Si0 3 )4(OH)

2

pris-

Density:

direction. Fracture conchoidal.

a = 1.531; p = (-),2V= 75°.

Birefringence:

y =

1.555;

1.570.

0.039.

Not diagnostic. Pyroelectric.

Spectral:

silky.

Luminescence: Pinkish orange (Green River, Wyoming).

Not determined.

Hardness:

Optics: Biaxial

Blue of various shades. Vitreous to

1

.

matic; massive, granular; fibrous.

Luster:

Distinct

Brittle.

Orthorhombic. Crystals slender

Crystallography:

Color:

2.60.

to

orange-brown

in

SW

3.8-4.11.

Occurrence: Very good

Cleavage:

in 2 directions.

Fracture uneven

to splintery.

in clays

from an

oil well,

20 miles oil

well in Uintah County, Utah.

a = 1.752-1.753;

Optics:

Occurs

west of Green River, Wyoming: also in clay from an

/}

=

1.782;

y =

1.815.

Mean

Very small,

Stone Sizes:

than

less

1

carat.

refractive index 1.75.

Biaxial

(

+ ),2V=

Comments:

88°.

Shortite

attractive mineral.

Birefringence:

0.063.

faceted stones. fore fragile

Not diagnostic.

Spectral:

Luminescence:

Name:

None.

ogy

An

Occurrence:

Shattuck Mine, Bisbee, Arizona: dense blue massive

psuedomorphous

after malachite.

material

rare, not overly

rarest of all

a carbonate and

is

is

there-

soft.

After Maxwell N. Short, professor of mineral-

at the University of

Arizona.

Katanga, Zaire: masses of

light

SIDERITE Series to Rhodochrosite (MnCOj) and Calcite (CaC0 3 ). Formula:

Ajo, Arizona: with other copper minerals. radial aggregates,

an exceedingly

alteration product of secondary cop-

per minerals. material; also

The

and

is

Cut gems are among the

FeCOi.

blue crystals; fibrous,

sometimes resembling

Crystallography: a pale blue

Hexagonal R (

).

Crystals

rhomb shaped:

also massive, granular; globular; oolitic.

pectolite.

Only cabochons can be cut, up

Stone Sizes:

Colors: to several

inches in length.

Comments:

Shattuckite

Pale yellowish brown, pale yellowish, pale green,

greenish gray, yellowish gray, grayish brown, reddish brown,

blackish brown; rarely almost colorless. is

often mixed with quartz,

and data often reported for properties may be erroneous. The cabochons are rich blue in color and very popular, but the material is not abundant and seldom seen on

Luster:

Vitreous, pearly, silky, dull.

Hardness: Density:

3.5-4.5.

3.83-3.96.

the market.

Name:

From

Cleavage:

Perfect rhombohedral. Brittle.

the Arizona locality, the Shattuck Mine.

Recent studies have shown that plancheite, a mineral similar to and often confused with shattuckite, is a dis-

Optics:

o=

Uniaxial (— ).

1.873;

e=

1.633.

7

SILICA

72

Birefringence:

Dispersion:

0.240.

Not diagnostic.

Spectral:

Luminescence:

None.

/}:

its;

hydrothermal ore veins; also

in

pegmatites; basaltic

rocks.

Colorado; Connecticut; Idaho. Austria; France;

Germany;

Minas Gerais.

and fine crystals. Quebec, Canada: brown rhombs up

Italy.

Brazil: large

Mt. Ste. Hilaire,

to

on edge.

15 inches

Panesqueira, Portugal: fine light brown crystals,

some

Greenland: rich brown, gemmy-looking crystals

Cornwall. England: greenish crystals,

some

transparent,

2.60, 2.25 (light

brown, Quebec, Canada).

from Portugese rough.

Luminescence: Weak reddish fluorescence in blue Burmese material. None observed in Sri Lankan stones. Occurrence: A mineral of metamorphic rocks, such as schists and gneiss; also granites. Idaho; South Dakota; Oklahoma; Pennsylvania; New York; Connecticut; Delaware; North Carolina; South Carolina. slovakia; Brazil; India; Madagascar; Korea; South Africa;

From

Greek sideros

the

referring to the

Sri

Lanka and Burma: green,

Fe and

C

is

(iron) in reference to

from the Greek of steel,

content.

Kenva: facetable

Stone Sizes: Faceted gems are usually small (under 5 and quite rare. Catseye gems are generally in the same size range, up to 10 carats, may be black, yellow, or

grayish green. SI: 5.9 (black catseye,

35

(= FIBROLITE)

Trimorphous with

Kyanite, Andalusite.

Al 2 SiO s

Crystallography:

.

Orthorhombic. Crystals prismatic,

rare;

usually fibrous masses. Colors:

South Carolina).

(fibrolite).

Geology Museum, London: 17

(fibrolite).

Comments: The fibrolite from Burma and Sri Lanka is known to gem collectors, and highly prized because of its great scarcity. Blue and greenish gems are lovely, although very

Formula:

crystals, pale bluish color to colorless,

S.g'. 3.27.

well

See: Quartz.

SILLIMANITE

blue, violet-blue facetable

fibrolite.

BM:

the composition. Chalybite

SILICA

violet blue.

carats)

Comments: Siderite is a difficult stone to facet, but cut gems of great beauty have been fashioned, especially

Name:

.

material; also from Sri Lanka, grayish green, chatoyant

as chalybite.

Stone Sizes: Siderite is not usually cut as cabochons because the massive material is not attractive, and the perfect cleavage makes cutting very difficult. Faceted siderite is rare and stones are usually small (1-5 carats).

NMC:

brown or greenish; brown or blue,

y: dark

Tanzania.

in cryolite.

known

be strong:

Canada; Ireland; Scotland; France; Germany; Czecho-

transparent. Ivigtut,

May

Pleochroism:

a: pale brown, pale yellow to green;

A widespread mineral in sedimentary depos-

Occurrence:

0.015.

difficult to cut.

Chatoyant material some-

times yields catseye fibrolites, which are also very rare.

The

material from

Kenya

is

just as attractive as

Burmese

fibrolite

but seems to be somewhat smaller

Name:

After Benjamin Silliman, mineralogist, of Yale

University. Fibrolite

is in

in size.

allusion to the fibrous nature of

this variety.

Colorless, white, gray, yellowish, brownish, green-

SIMPSONITE

ish, bluish, violet-blue.

Vitreous to

Luster:

Hardness: Density:

6.5-7.5.

compact

1

Hexagonal. Crystals tabular, prismatic;

also in crystalline masses. varieties 3.14-3.18.

Colors: Perfect

3

Crystallography:

3.23-3.27;

Cleavage:

ALTa 0,3(OH).

Formula:

silky.

Colorless, pale yellow,

cream white, light brown,

direction. Fracture uneven. Brittle.

orange. Optics: Biaxial

(

a = 1.654-1.661; /J = + ),2V= 21-30°.

Birefringence: Spectral:

weak

1.658-1.662;

y=

1.673-1.683.

Vitreous, adamantine.

Hardness:

7-7.5.

0.020.

Distinct lines (Sri Lanka) at 4620 and 4410,

at 4100.

Luster:

Density:

Cleavage:

5.92-6.84.

None. Fracture conchoidal.

Brittle.

SMALTITE o

Optics:

=

2.034; e

=

peridot: bands at 4930, 4750, 4630 (absent in peridot),

Uniaxial (— ). Birefringence:

None.

Luminescence:

Not diagnostic.

Luminescence: tralia),

4520 and 4350; general absorption of the the spectrum.

0.058.

Pleochroism: Spectral:

In

SW,

bright pale yellow (Bikita,

Zimbabwe), medium

In granite pegmatites, usually with biotite.

Zimbabwe; Alto do Giz, Ecuador; Kola PeninUSSR. Onca and Paraiba, Brazil: facetable material.

Sri

Lanka: major source of gem

gem

bles in

Stone Sizes: occurs

general, stones are only seen from Brazil

A

typical size

is

and Australia.

0.5-1 carat.

should be considered extremely rare because clean matea very small percentage of the limited supply of

simpsonite that has been found.

Name:

sinhalite, as rolled peb-

though quite rare, The normal range is 1-20 carats, but gems over 100 carats have been found from time to time. Interestingly, sinhalite,

in large sizes in the Sri

Lankan

gravels.

SI: 109.8 (brown, Sri Lanka); 43.5, 36.4 (brown, Sri Lanka).

PC: 158

(Sri

Lanka) — this

is

the largest

known

sinhalite

gem.

Comments: Simpsonite is an extremely rare gemstone. The material from Western Australia is bright yelloworange and very beautiful. The mineral is hard and durable, with no cleavage, and could easily become a popular gemstone if it were more abundant. Gems over 1 carat rial is

in lime-

gravels.

Tabba Tabba, Western Australia; facetable yellowish

cm, but

contact metamorphic mineral

some gemmy areas. Burma: one rolled pebble noted.

crystals.

Crystals have been found up to 5

None.

Warren County, New York: no gem value. Northeast Tanzania (in a skarn): pink to brownish pink,

Bikita,

only tiny stones have been cut from available rough. In

end of

violet

stones at granite contacts; alluvial.

sula,

Stone Sizes:

A

Occurrence:

bright blue-white (Western Aus-

pale yellow (Ecuador) or light blue (Paraiba, Brazil).

Occurrence:

Very distinctive; similac to but distinct from

Spectral:

1.976.

173

After Dr. E. S. Simpson, former government

DG:

24.76 (Sri Lanka).

NMC:

21.99 (light brown, Sri Lanka).

Long thought to be brown peridot, sinhawas investigated in 1952 and found to be a new mineral. When cut, it is richly colored, bright, and attractive, and resembles citrine, peridot, or zircon. Large gems are very rare, but smaller stones are available in the marketplace. Some people have reported that it was

Comments: lite

easier at times to find a large sinhalite for sale than a

small one, however, as rough pebbles from Sri

mineralogist of Western Australia.

Lanka are

often large.

Name:

SINHALITE

MgAlB0

Formula:

ish

4

SKUTTERUDITE

light pink,

Ceylon (now

Sri

See: Smaltite.

Formula:

(Co,Ni)Asi

,.

Considered to be an arsenic-

deficient Skutterudite.

brownish pink.

Crystallography:

Vitreous.

Luster:

for

SMALTITE

Yellowish, yellow-brown, dark brown, green-

brown,

word

.

rolled pebbles.

Colors:

the old Sanskrit

Orthorhombic; found only as grains

Crystallography:

and

From

Lanka), sinhala.

Isometric. Crystals cubic to octahe-

dral; massive, fine-grained.

Hardness:

6.5-7.

Colors: Density:

Cleavage:

Not determined.

a = 1.665-1.676; /3 = 1.697; y = 1.705-1.712. Lanka = 1.669/1.702/1.706).

Biaxial

(-),2V=

Birefringence:

Pleochroism:

brown.

may

tarnish gray to

iridescent.

Optics: (Sri

Silver gray to tin white;

3.475-3.50.

Metallic; opaque.

Streak:

Black.

Hardness:

56°.

Density:

0.035-0.037. Distinct: pale brown/greenish

Luster:

brown/dark

Cleavage:

5.5-6.

-6.1. Distinct 2 directions. Fracture

choidal. Brittle.

uneven

to con-

7

SMITHSONITE

74

Occurrence: veins, with Ni (

Occurs in mediumand Co minerals.

to high-temperature

Ontario, and British Columbia. Canada.

district,

Chile; Switzerland; Germany. to

any

size

from

massive material.

Comments: cabochons.

is

a collector's oddity, cut only as

seldom seen

in

collections since

it

is

not

especially distinctive, with a color resembling other metallic

Name: From its use as a source ment smalt, which is blue.

of cobalt for the pig-

SMITHSONITE ZnCO, +

Formula:

Mexico: pink and bluish

may be

Fe, Ca, Co, Cu,

Mn, Cd, Mg,

Pb.

Hexagonal (R). Crystals rhombohecompact, stalactic.

Crystallography:

crystals to

1

crusts;

much

variation in color.

Beautiful cabochons up to

cut from the massive material from

many

is

The pink

material from

carats could be considered exceptional. 45.1 (dark yellow, emerald-cut,

Tsumeb).

The blue-green smithsonite from New Mexico has been popular with collectors for many years. Pinkish colors are due to cobalt, yellow to cadmium. The low hardness of smithsonite makes it unsuited for jewelry, but properly cut faceted gems are magnificent. The dispersion is almost as high as diamond, and faceted stones have both rich color and lots of fire. Among the most beautiful are the yellowish stones from Tsumeb, Comments:

White, gray, pale to deep yellow, yellowish brown brown, pale green, apple green, blue-green, blue, pale to deep pink, purplish, rarely colorless.

Name:

to

bequest founded the Smithsonian Institution

After James Smithson, the benefactor whose in

Wash-

ington, D.C.

Vitreous to pearly, earthy, dull.

Hardness: Density:

SOAPSTONE

4-4.5.

See: Talc.

4.3-4.45.

Perfect rhombohedral. Brittle.

Cleavage:

o

=

1.848; e

=

SODALITE

(rich in S); Sodalite

1.621.

Na,AL(Si0

Formula:

Birefringence:

Hackmanite

Variety:

Group.

Uniaxial (— ). 0.227.

4

).iCl.

Isometric. Crystals rare (dodecahedral):

Crystallography:

massive, granular.

Dispersion:

Other

known

only from the African localities, and stones over 10

Colors:

Spectral:

Mexico

especially lovely. Facetable crystals are rare,

Namibia.

Optics:

inches

New Mexico,

dral; massive, botryoidal,

Luster:

cm.

Sardinia, and other localities. Crusts in-some localities

PC:

and arsenides.

sulfides

Zambia: transparent

Hill,

are several inches thick.

Smaltite It is

Broken

Stone Sizes:

Cabochons could be cut

Stone Sizes:

crystals, also

green — facetable. Australia: yellow.

Colorado.

(ili/ornia;

Cobalt

Tsumeb, Namibia: yellowish and pinkish

None.

Luminescence:

0.037.

Colors:

Not diagnostic.

Tests:

Effervesces in

warm

acids.

SW, medium whitish blue (Japan), blue-white (Spain), rose red (England), and brown (Georgia, Sardinia). In LW, greenish yellow (Spain) and lavenLuminescence:

Colorless; white, yellowish, greenish, reddish;

usually light to dark blue.

In

Luster:

Vitreous; greasy.

Hardness: Density:

5.5-6.

2.14-2.4; massive blue -2.28.

der (California).

Poor. Fracture uneven to conchoidal. Brittle.

Cleavage:

Occurrence: Smithsonite is a secondary mineral in the oxidized zone of ore deposits. Colorado; Montana; Utah. Germany; Austria; Belgium; France; Spain; Algeria;

Optics:

Isotropic;

Dispersion: Spectral:

N=

1.483-1.487.

0.018.

Not diagnostic.

Tunisia.

New Mexico: blue and blue-green,

LW,

usually orangy red to violet;

Luminescence:

In

massive crusts, fine color.

also dull pink in

SW

Marion County, Arkansas: yellow, banded crusts. Laurium. Greece: fine blue and green crystals.

Hackmanite. from Dungannon Township, Ontario, Canada: bright pale pink in SW, bright yellow-orange in LW. Mineral is white, may turn raspberry red after exposure

Kelly,

Socorro County,

Sardinia. Italy:

banded yellow material.

(Guinea).

SPHALERITE to

SW;

color fades rapidly

in sunlight,

and cycle

is

repeatable.

Occurrence:

nepheline syenites and related rock

In

types.

Montana; South Dakota; Colorado; Arkansas; Maine;

New Hampshire;

Occurrence: In the Alai Range. Tadzhik, SSR. platy masses up to 10 x 7 x 4 cm, in a vein pegmatoidal body compositionally like an alkalic granite. Also occurs at the Wessel Mine. Karuman. North Cape Province. South Africa.

Comments:

Massachusetts.

175

Sogdianite

is

an extremely rare mineral,

The

Greenland; Langesundsfford, Norway; Rqjasthan, India; Bahia, Brazil; USSR; Scotland; Ruma, French Guinea.

suitable for cabochons.

Bancroft. Ontario, Canada: massive, deep blue material,

mixed with other minerals, so the SG and hardness are variable. Chemical analysis may be required to differentiate sogdianite from sugilite, but the latter is far more

reddish streaks.

Dungannon Township.

Ontario. Canada: hackmanite;

Columbia, other locations. Ohopoho. northern Namibia: extremely intense, solid blue material, sometimes very translucent, almost transparent (N = 1.486). from

also sodalite

British

Massive blue material provides blocks for

Stone Sizes:

cabochons or spheres especially from Canada and

material

is

color

is

striking

hard enough to take a good polish.

and the usually

It is

abundant.

Name:

From Sogdiana,

the

name

of an ancient state in

Middle Asia.

SPESSARTINE

See: Garnet.

carvings, decorative objects, and to almost

any desired

Namibia.

Much

size,

sodalite

is

carved

SPHAEROCOBALTITE

Germany, made into boxes and beads. Faceted gems are sometimes cut from very translucent Namibian material, but these gems are very dark and not very transparent,

SPHALERITE

except

Crystallography:

in tiny sizes

Comments:

(under

Sodalite

1

carat).

extremely rich

is

in color, also

making it very desirable among hobbyists. Faceted gems are very lovely despite quite tough

and easy

to cut,

their lack of transparency ful.

See: Calcite.

Idar-Oberstein,

in

because the color

is

Formula:

(

ZnS +

BLENDE)

dimorph of Wurtzite.

Fe.

Isometric. Crystals widespread, in vari-

ous shapes; massive, cleavable, granular. Colors:

Colorless (very rarely); black (rich

in Fel,

brown,

orange, yellow, green, orange-red, white gray.

so beauti-

Sodalite group minerals are also responsible for the

fine color of lapis lazuli, another blue

Name:

In allusion to the

gem. N

sodium content.

248

SOGDIANITE 246 /v/

(K.NahLMLiTcAhTihZ^SizO^.

Formula:

sive, platy.

Luster:

(calc.

242

4 12

240

408

238

404

236

400

Hexagonal; crystals not observed; mas-

Crystallography:

Color:

SG.

244

Bright violet.

Vitreous to waxy.

Hardness:

7,

if

2.90, pure (South Africa

Density:

=

pure (South Africa

=

5-6).

2.76). S.G.

N

Cleavage: Optics:

Perfect

o

=

396

direction.

1

1.606; e

=

392

1.608.

Uniaxial (— ). 10

Birefringence:

15

20

0.002. Mol.

Pleochroism: Spectral:

4370;

Not reported.

Luminescence: in LW.

at

%

30

35

40

388

FeS

Refractive index (N) and chemical composition in tutes for Zn, in the formula (Zn,Fe)S.

specific gravity plotted against sphalerite, in which Fe substi-

Diagnostic, sharp lines at 4110, 4190, and

weak bands

25

4880-4930 and 6300-6450.

Very weak dark red

in

SW, weak

violet

Adapted from W. A. Deer, R. A. Howie, and J. Zussman. 1 962, The Rock Forming Minerals, vol. 5 (New York: Wiley), p.

174.

SPHENE

76

7

Streak:

Pale brown to colorless.

Luster:

Resinous to adamantine.

Hardness:

bright, and the dispersion is about four times that of diamond. Consequently, faceted gems are alive with fire and color, which is strong enough to be seen even against the rich body color. Pale-colored or colorless sphalerite

3.5-4.

is

3.9-4.1.

Density:

Perfect dodecahedral. Brittle.

Cleavage: Optics:

Isotropic;

N = 2.37-2.43 (Spanish material 2.40).

0.156 (extremely high).

Dispersion:

Sometimes 3 bands seen 6670, and 6510 due to cadmium. Spectral:

in the

red at 6900,

extremely rare, but gems of the other colors are easily

no shortage of facetable rough. is too soft and fragile to wear in jewelry. It has dodecahedral cleavage (six directions) and the material is rather brittle and easily scratched. It could be a very important gem if harder and less fragile. available, as there

is

Sphalerite, for

beauty,

Larger stones (over 20 carats) usually have some inclusions, as well as veils

ent stone

Luminescence: Bright orange-red to red in LW, SW, from many localities. Material from Otavi, Namibia is triboluminescent. Occurrence: Sphalerite is the chief ore of zinc, the most abundant zinc mineral, and is common in lowtemperature ore deposits, especially in limestones; also in sedimentary rocks; hydrothermal ore veins. Wisconsin; Montana; Colorado; Idaho; Arizona. Canada; Tsumeb, Namibia; England; Scotland; Sweden; France; Germany; Czechoslovakia; Rumania: Australia.

all its

is

and flaws, so a completely transpar

also considered rare. Cutting

is

and the appearance of a cut gem depends

all-important, largely

on the

quality of the surface polish.

Black sphalerite sphalerite in

Name:

From

because

is

called marmatite. and the

European schools the

Greek

is

word

for

blende.

sphaleros,

meaning treacherous,

often resembles galena (lead sulfide) but yielded

it

no lead when first smelted. In Europe sphalerite is called blende, from the German blenden, meaning to dazzle. Marmatite, the black variety, at

Marmato,

is

named

after the locality

Italy.

Missouri Oklahoma, Kansas: so-called Tri-State Region, heavily mineralized by lead and zinc, with

many

locali-

and operating mines.

ties

Tiffin,

SPHENE (TITAN1TE) Formula:

CaTiSiOs.

Ohio: red.

Colorado; Utah: may be transparent. Franklin,

New

transparent variety

known as cleiophane. gem locality, large

Santander, Spain: major

Monoclinic. Crystals often wedge

Crystallography:

Jersey: almost colorless to pale green,

shaped, well formed, flattened, prismatic; also massive,

compact. cleavages of

Colorless, yellow, green, gray, brown, blue, rose

Colors:

red-orange color.

Cananea, Sonora, Mexico: fine green transparent material, often pale colored and color zoned, sometimes

red, black. Often zoned.

Color correlates with Fe content:

green and yellow due to low Fe; brown and black due to high Fe.

yellow.

Kipushi, Zaire: dark green material containing elevated

amounts of Co and

Fe.

Gems

Stone Sizes:

Hardness:

of hundreds of carats could easily

be cut from the large reddish material from Spain. This material

is

also

cleiophane from

sometimes cut as cabochons. Green

New Jersey

large as 15 carats.

Adamantine

Luster:

Mexican gems could be cut

5-5.5.

3.45-3.55.

Density:

Cleavage:

has yielded faceted gems as Optics: to 50

Biaxial

(

to resinous.

Distinct

1

direction. Brittle.

a = 1.843-1.950; /J - 1.870-2.034; y = 1.943-2.110. + ), 2V — 17-40°; lower indices with lower Ti

carats.

SF 73.3, 68.9 (yellow-brown, Utah); New Jersey); 48 (yellow, Mexico);

content. 59.5 (yellow-green, 61.9, 45.9 (yellow, Birefrin-

Spain).

CA:

Madagascar

100.1 (dark orange, round, Spain).

24.8 (gray-green, Mt. Ste. Hilaire, Quebec).

Comments: all

gence

S.G.

0.160

3.52 3.53 3.52 3.53

150.3 (dark red-brown oval, Spain).

NMC: PC:

Locality

cut gems.

Sphalerite It

occurs

in

is

one of the most beautiful

of

2.070 2.080 2.099

Mexico Sri Lanka

1.910 1.908 1.909

Brazil

1.911

Birefringence:

0.100-0.192.

shades of green, yellow, orange,

brown, and fiery red (all colors due to Fe) that are enhanced by faceting. The luster can be adamantine, like diamond, so cut gems with a good polish are very

Dispersion:

0.051 (strong).

—

0.181

0.190

—

SPINEL Pleochroism: Moderate to strong: a = pale yellow; P = brownish yellow; y - orange-brown. Sometimes (blue crystals): colorless/blue.

Sometimes see "didymium" or

Spectral:

trum. This

is

gems are brittle and easily The best-looking stones are round brilliantChrome sphene from Baja is the color of fine emer-

unfortunately, low, and

is,

scratched. cut.

ald

and very

rare earth spec-

especially distinctive in Sri

The

carat.

Lankan gems

if

clean and larger than

gem

None.

from Indian material.

Name:

Sphene occurs as an accessory mineral in in metamorphic rocks such as schist

Sphene

is

from the Greek sphenos (wedge), in wedge-shaped crystals. the dark brown to black color of the

igneous rocks, and

allusion to the characteristic

and granite, often in fine crystals. York; Canada: brown and black crystals. Madagascar: green crystals, some large.

original titanium-rich specimens.

Titanite alludes to

New

Zillerthal, Austria; Grisons. Switzerland:

Sri

both

gem local-

SPINEL

Burma: some gemmy material found.

Pakistan;

substitutional elements.

Isometric. Crystals octahedral; also

Various shades of red, blue, green; also brown,

Colors:

black, gray,

lilac,

purple, orange, orange-red, rose, nearly

colorless.

Vitreous.

Luster:

Hardness:

7.5-8.

gemmy. Density:

Stone Sizes: Sphene is very rare in clean stones over 5-10 carats. Even a 5-carat flawless gem is considered a

and

+ many

as grains, massive.

South India — yellow, brown, green. Baja, Mexico: yellow-brown, brown, green, dark green (Cr-bearing) gemmy crystals. This may be one of the world's major sphene deposits, with gemmy crystals to 4 inches. Minas Gerais, Brazil: twinned yellowish to greenish crys-

rare

4

2

Crystallography:

Mettur, India: about 30 miles from Salem. Tamilnadu,

often

MgAl

Formula:

Lanka: dark brown, yellowish green, honey yellow.

tals,

Spinel Group.

past years.

ities in

1

material has a sleepy

is not as bright as that from Baja. Some of the and most spectacular green gems have been cut

largest

Occurrence:

rare, especially

Brazilian yellow

look and

(sharp lines at 5860, 5820, 5300, and others).

Luminescence:

177

3.58-3.98;

fine stone. Indian material generally cuts to

Dispersion:

The

3.58-3.61; see table below.

None. Fracture conchoidal.

Cleavage:

about 10 carats, Madagascar material to perhaps 15 carats, and Brazilian yellow stones over 5 carats are scarce. Sri Lankan gems are mainly under 10 carats. Burmese stones over 20 carats are known, but Baja,

gems

0.020.

spinel group

is

fairly large,

with widely varying

chemistry and properties. All are isometric oxides of

Mg,

Fe,

and Zn with aluminum and traces of other

elements.

Mexico, has the potential for producing some of the largest faceted gems. Chrome sphene of fine color is

There is a continuous solid solution between spinel and gahnite, and refractive index and specific gravity

extremely rare, especially over 2-3 carats.

both vary with chemistry, as might be expected.

SI: 9.3 (golden, Switzerland); 8.5 (brown,

New

York); 5.6

Refractive index variation with color, as generally ob-

yellow-brown, Mexico).

PC: 63

carats (green); 106 (intense dark green, from

India, square emerald-cut

mous

DG:

served in gems:

dispersion

red: 1.715-1.735;

and near flawless with enor-

blue: 1.715-1.747;

— by far the world's largest cut sphene).

others: 1.712-1.717 (normal).

4.95 (red!).

NMC:

Spectral:

50.75 (green, Brazil, very fine).

Very distinctive spectra, useful

Red and pink: chromium spectrum,

in identification.

has broad band at

Comments:

5400, plus absorption of violet; group of fine lines in the

fire

red

Sphene is a magnificent gemstone, rich in and with superb, intense body colors. The hardness

Formula Spinel

MgAI 2

Gahnite

ZnAI 2 4 (Mg,Zn)AI 2

Gahnospinel

4

Hercynite Ceylonite (pleonaste)

(Mg,Fe)AI 2

Picotite

Fe(AI,Cr) 2

Galaxite

MnAI 2

FeAI 2

4

4

4

4

4

may be

fluorescent "organpipe" lines.

R.I.

S.G.

1.719 1.805

3.55-3.63 4.0-4 62 3.58-4.06 4.40 3.63-3.90 especially 3.80 4.42 4.04

1.725-1.753+ 1.835 1.77-1.78

— 1.92

Color various (above)

deep green blue,

dark blue

black, dark colors

very dark colors

dark green

deep

to

black

red to black

SPINEL

178

Gahnospinels from

Sri

Lanka

Afghanistan: fine red spinel, source of

FeO(%)

N

SG.

0.14 7.18 10.27 12.98

2.34

1.716 1.723

3.60 3.72

1.731 1.737

377

47

18.21 24.81

1.93 1.90

1.747 1.752

ZnO(%)

1.92

2.52 1

Lanka: worn pebbles in wide variety of colors, espeand blues; all the blue ones have a trace of Zn; many from Sri Lanka are black. The rare cobaltian variety is unique to Sri Lanka. Burma: spinels from the gem gravels, often as perfect

3.86 3.97 4.05

octahedra.

6860, 6750, plus 6350, 5850, 5550 and

5080. {Note: This iron spectrum

is

distinctive vs. the cobalt

blue of synthetic spinel.) Nigerian blue gahnite also has

bands

at

7000 and 5700

like

those seen in spinel.

Mauve and pale blue: similar spectrum to blue, but weaker. Reds and pinks: crimson

Luminescence:

SW;

in

LW,

also

red in X-rays; no phosphorescence.

Blue: inert in UV.

Deep purple:

red in

LW,

essentially inert

SW,

lilac in

X-rays.

Pale blue and violet: green inert in

in

LW,

X-rays, essentially

SW.

Cambodia and Thailand:

spinels in alluvial gravels.

Stone Sizes:

known up

ats, in

some

inclusions are distinctive. Silk, as in sapphires and

Angular inclusions known as spangles are seen; distinctive are rows and swirls of tiny octahedra of another spinel, such as magnetite (FeFe 2 4 ). Also characteristic are iron-stained films and feathers, especially at edges of gems. Also zircon inclusions and darkened surrounding areas, zircon haloes, (due to radioactivity), accompanied by feather around zircon, due to stress cracking. Natural spinels also contain octahedral-shaped cavities (negative crystals), someruby,

is

times

seldom seen

filled

with calcite.

Mogok, Burma: Sri

in spinel.

spinel.

R.I.

=

1.793.

gemmy

gahnite.

Australia: gahnite.

Japan: galaxite.

USSR: gemmy,

fine pink material

Pamir Mountains. New Zealand: gahnite.

hundreds of car-

SI: 45.8 (pale purple, Sri Lanka); 36.1 (indigo blue,

Burma);

34 (red, Burma); 29.7 (pink-violet, Sri Lanka).

BM: deformed

red octahedron from Sri Lanka, 520; another crystal, 355. PC: 11.25 (Sri Lanka, superb cobaltian spinel, intense blue emerald cut). Louvre, Paris: fine red gem, 105.

AMNH: 71.5

(red, Sri Lanka).

Crown Jewels of England: Black Prince's Ruby, red spinel, estimated at 170; Timur ruby, red spinel, 361. Diamond Fund, Moscow: fine red spinel, over 400. Banque Markazi, Teheran, Iran: red stone over 500, another over 200, one about 225.

because

it

Spinel

is

Ruby and

gem

an important

historically

has been confused with other gemstones,

especially ruby. Large red

the

Timur Ruby

gems such as the Black Prince's in the Crown Jewels of England

have proven to be fine large red spinels (ruby ancient times this material was

known

spinel). In

as Balas ruby.

Star spinels have occasionally been cut, with 4-rayed

and colored gray or grayish-blue to black (from Burma); a 6-rayed star can be seen in such material if

stars,

oriented along the 3-fold symmetry axis of the crystal, that

is,

parallel to the

edges of an octahedral face.

Fine red spinels over 3 carats are very difficult to Asia, which has

from Kuchi Lai

in

the

made gem

dealing very difficult. Large

spinels of other colors are available from time to time.

The

Occurrence: Spinels are found in metamorphic rocks and their weathering products. Especially found in contact deposits (marbles and limestones). California: Montana; New York; Colorado; New Jersey; Massachusetts; Virginia. Canada; France, Italy; Germany; Finland; India. Sweden: gahnite. Jemaa, Nigeria: fine blue gahnite, S.G. = 4.40-4.59,

Madagascar: blue,

to

obtain because of the political upheaval in Southeast

calcite, apatite, dolomite, olivine.

Lanka: zircon, sphene, baddeleyite, phlogopite, apa-

tite,

Spinels are

various colors.

Comments: Spinels are generally free of inclusions, but

Inclusions:

gems

cially pinks

:

at

large

Sri

Blue iron spectrum has lines in blue especially at 4580, plus narrow line at 4780 and weak lines at 4430 and 4330;

two strongest are

many

of the ancient world.

value of fine red spinels

is

sure to increase due to

and a general interest among the gem-buying public. their scarcity

Alexandritelike spinels are

when viewed

in

known

colored stones

that are grayish

and amethystine color in incandescent light. These are quite rare and usually small. Some stones from Sri Lanka change from violet (daylight) to reddish violet, due to the presence of Fe, Cr, and V. Remarkable blue stones containing cobalt may be difficult to distinguish from flux-grown or flame-fusion synthetics. However, flame-fusion synthetics often display chalky whitish-green fluorescence in SW-UV and strong red in LW. The synthetics also display "crosshatched" or "snakelike" anomalous birefringent patterns blue

in daylight

in cross polarized light.

Natural cobaltian spinel also

SPODUMENE shows absorption bands

at

4340, 4600, and 4800A, which

are not observed in synthetic material. is

The band

at

4600

Names: The name spinel is of doubtful origin; it may come from the Latin spina (little thorn), alluding to spine-shaped crystals, but is

district, California: fine

kunzite,

gem

quality, plus

yellow-green spodumenes. Hiddenite. North Carolina: type locality for emerald

especially diagnostic.

spinel. Ceylonite

Pala

179

this is

named

not a

common

after the locality,

green spodumene; also at Stony Point. North Carolina: this material contains Cr and shows Cr spectrum. Madagascar: kunzite, green and yellow spodumene, gem

habit for

Ceylon

(now Sri Lanka), and gahnite after the Swedish chemist, J. G. Gahn. Galaxite is named after the plant of the same name, which grows in an area where the mineral was first discovered, near Galax, Virginia.

quality.

Minas Gerais,

Brazil:

yellow spodumene,

major gem

some

locality for kunzite.

green. Material from Brazil

contains no Cr, and green varieties are not hiddenite.

Afghanistan:

all

colors,

some

very large crystals;

gem

quality.

Burma: gem

SPODUMENE

Color

quality.

varieties: Kunzite, Hiddenite.

Very large spodumene crystals exist, as in South Dakota, but these are not gem quality. Kunzite

Older name: Triphane.

Stone Sizes:

Formula:

do reach a size of many pounds while retaining and transparency, and very large gems have been cut from nearly all the colors. PC: -137 (deep yellow, Afghanistan), also 1160, 1240

LiAlSi 2 0<,.

crystals

Monoclinic. Crystals prismatic,

Crystallography:

flattened, often corroded; massive.

Colorless, gray, pale to dark yellow, pink, vio-

Colors: let,

pale green, deep green, blue-green, blue.

(yellow); 720 (kunzite, spectacular dark color, Brazil). SI: 327 (yellow, Brazil); 71.1 (yellow,

Madagascar); 68.8

(yellow-green, Brazil); 880 (kunzite, Brazil); 336, 297

Vitreous.

Luster:

fine color

(deep violet, Brazil); 177 (kunzite, California);

Hardness: Density:

6.5-7.5.

3.0-3.2;

ite,

gems

HU:

usually 3.18.

kunzite crystals from Pala, California

Naturhistorisches

Cleavage:

Perfect

1

direction. Fracture conchoidal.

Brittle.

Optics: Biaxial

(

a = 1 .653-1 .670; f> = + ),2V= 55-68°.

Birefringence:

1

.660-1 .669;

y=

1

.665-1 .682.

x 0.6 cm. Denver Museum: 296.7

CA: 122.24 (light green LA: 1260 (kunzite).

kunzite,

Pronounced:

pink crystals: purple-violet/colorless;

green crystals: green/blue-green/colorless to pale green. Spectral: Not diagnostic in kunzite. Hiddenite shows a chromium spectrum, with doublet at 6905/6860 and weaker lines at 6690 and 6460, broad absorption at 6200. Yellowgreen spodumene shows a distinct band at 4375 and a weaker band at 4330.

Luminescence: Kunzite: golden pink to orange in LW, weaker in SW, orange in X-rays (with phosphorescence); X-irradiated kunzites may change color to blue-green, but this color disappears in sunlight. Yellow-green spodumene: orange-yellow in LW, weaker in SW., strong in X-rays but no color change in body of material. Hiddenite gives orange glow in X-rays, with phosphorescence. Occurrence: A mineral of granite pegmatites. King's Mountain, North Carolina; Maine; Connecticut; Massachusetts. Etta Mine. South Dakota: tals,

up

to

immense white

40 feet long, embedded

Museum, Vienna:

— 2200 grams.

hiddenite crystals,

(kunzite, Brazil).

cushion-cut, Brazil).

Spodumene is a very attractive material some pleasing colors. The pink variety. the best known, but yellow gems from Brazil

Comments:

0.014-0.027.

0.017.

Pleochroism:

(kunz-

3

and occurs Dispersion:

11. 6

North Carolina).

in rock.

to gray crys-

is

in

and Afghanistan are also lovely (Afghanistan produces much deeper yellow material than Brazil) as are the light blue-green stones from the same localities. Hiddenite is known only from North Carolina and is extremely rare and costly; the color is a medium-deep green, never the intense dark green of fine emerald, and crystals are always very small.

The

perfect cleavage of

spodumene makes

cutting

and most hobbyists have some trouble with the material. Spodumene should be worn with some caution to prevent breakage. The pleochroism is extremely

intense,

difficult,

and cut stones should be oriented with the table

perpendicular to the long axis of the crystal for the best effect.

Kunzites of jewelry size are abundant and

inexpensive.

Name:

Spodumene

is

from the Greek spodumenos (burnt

to ashes), in describing the

common

named after G.

gray color of the

Kunz, noted author and gemologist for Tiffany and Co. Hiddenite is named after W. E. Hidden, one-time superintendent of the mine in North Carolina where it was found. mineral. Kunzite

is

F.

SPURRITE

780

SPURRITE

Optics:

Ca

Formula:

Biaxial

Si20nC03.

s

ally

a = 1.739-1.747;/}= + ),2V= 82-90°.

1.745-1.753;

y=

1.752-1.761.

Indices increase with iron content.

Monoclinic. Crystals anhedral; usu-

Crystallography:

(

0.011-0.015.

Birefringence:

massive, granular.

Dispersion:

Colors:

Gray, lavender-gray, purple.

Luster:

Vitreous. Translucent.

0.023.

Pleochroism:

Distinct: colorless/yellow or red/golden

yellow.

Hardness: Density:

5.

Cleavage:

Biaxial

Distinct

a =

Optics:

Not diagnostic. Weak band

Spectral:

1.640;

(-),2V =

Birefringence:

1

/J

Zincian staurolite: strong broad bands at 6100 and 6320, weaker narrow bands at 5315; spectrum absorbed beyond

direction.

=

1.674;

y=

4900.

1.679.

40°.

Luminescence:

0.039.

Not reported.

Pleochroism:

Not reported.

Spectral:

Luminescence: Occurrence:

Not reported.

A contact

mineral

None.

Occurrence: Staurolite is a mineral of metamorphic rocks, such as schists and gneiss. New Hampshire; Maine; Vermont; Connecticut. Canada; France; USSR; Zambia; Scotland. Virginia, North Carolina, Georgia: abundant fairy crosses and twinned crystals. New Mexico: fine twinned crystals.

Not reported.

Dispersion:

in limestones.

Crestmore, California; Tres Hermanes,

New

Brazil: facetable crystals rarely found.

Mexico.

Switzerland: occasionally a facetable crystal

County Antrim, Ireland. Velardena mining district, Durango, Mexico.

Lusaka, Zambia: Lusakite.

Comments:

Stone Sizes:

Scawt

This attractive but rather rare mineral has

seldom been cut as a gemstone. Polished slabs and rough material appeared in 1986 at a mineral show in substantial quantities, however. This material is Mexican, translucent to opaque, and medium to dark purple in color. The hardness and tenacity are adequate for use as cabochons. After the American geologist, Josiah

Edward

if it is, it is

Staurolite

is

almost never transparent, but

SI: 3.0 (dark

brown,

Brazil).

Comments:

Faceted staurolites are extremely rare and always small and dark in color. Staurolite forms very

gems are too dark to be Nonetheless they are true rarities

interesting crystals, but cut

and lack

fire.

for their scarcity.

Zincian staurolite, though very rare,

STAUROLITE

Crystallography:

Monoclinic (pseudo-orthorhombic).

Crystals prismatic, typically twinned at 60° or 90°, the latter

termed fairy crosses; massive.

Dark brown, reddish brown, yellowish brown,

Colors:

is

lighter in color

and more attractive as a cut gem; S.G. or + Co.

tiny, less

faceted from Brazilian or Swiss

in general,

crystals.

and prized

(FcMg^nfcAUSUCMOH) + Zn

encountered

then very dark. Cut stones are always

than 2 carats

attractive

Spurr.

Formula:

is

in schists.

Hill,

Name:

at 5780, strong at

4490.

3.0.

3.79, indices

1.721-1.731; trichroic: green/red/yellow.

May

brown

in daylight.

incandescent

in

light,

yellow-green

be red-

is a deep blue, strongly pleochroic cobaltian from Lusaka, Zambia.

Lusakite staurolite

Name:

From

the

Greek stauros +

lithos.

meaning stone

cross.

brownish black. Luster:

Vitreous to resinous.

Hardness: Density:

Cleavage: Brittle.

See Talc

STIBIOTANTALITE

7-7.5.

Formula:

3.65-3.83.

Distinct

STEATITE

1

direction. Fracture conchoidal.

Series to Tantalite.

Sb(Ta,Nb)0 4

Crystallography:

.

Orthorhombic. Crystals prismatic, stri-

ated, often twinned, massive.

1

STOLZITE Dark brown

Colors:

brown, reddish

to light yellowish

yellow, yellowish gray, reddish brown, greenish, yellow.

Cleavage:

Perfect

Optics:

Yellow-brown.

Luster:

Vitreous to resinous.

o

=

1.518.

Uniaxial (— ).

Shadow edge seen

at

about

1.53.

0.027.

5-5.5.

Pleochroism: Density:

=

1.545; e

Birefringence:

Hardness:

direction. Friable, flexible laminae

(inelastic).

Often zoned. Streak:

1

181

Light to dark red.

7.34-7.46.

Typical Cr spectrum: 3 lines

Spectral:

Cleavage:

Distinct

1

direction. Fracture subconchoidal.

in

the red at

6655 to 6300.

Brittle.

Optics: Biaxial

(

a = 2.37; fl = + ), 2V=75°.

y =

2.40;

Luminescence:

None.

2.46.

Occurrence:

In serpentine rocks, usually associated

with chromite. Birefringence:

Dispersion :

0.090.

0.

Black Lake, Quebec, Canada. Dundas, Tasmania: mixed with green serpentine. Transvaal, South Africa: Algeria.

46.

Not diagnostic; may show "didymium"

Spectral:

lines.

In granite pegmatites, often in good crystals. Topsham, Maine. San Diego County, California: gemmy

Occurrence:

color

is

usually lilac to purplish, often veined with green

serpentine, and the color combination

crystals.

Varutrask, Sweden.

Wodgina district Western

Australia:

as rolled pebbles. Brazil;

Massive material is sometime cut into cabochons, but the material is usually used to carve decorative objects such as ashtrays and bookends. The Stone Sizes:

None.

Luminescence:

Mozambique: gemmy

is quite handsome. Blocks weighing several pounds are obtainable.

Comments: crystals. is

This material

Stone Sizes:

The

stones over 10 carats.

is

virtually

material

unknown

is

in

fairly rare,

Stichtite

is

not facetable, but the pink color

quite striking in cabochons. Cut stones are especially

when

there are other minerals present to add

cut

beautiful

but

splashes of green and yellow. This material

transparent specimens are extremely rare.

resembles a pink, granular material from the

DG:

to as canasite.

4.65 (Brazil).

SI: 7.3 (yellow, Brazil); 2.5 (brown,

Comments: erite,

Cut

Name:

stibiotantalite strongly resembles sphal-

but the luster

is

much

less brilliant (sphalerite

be adamantine), and stibiotantalite ily

Mozambique).

is

usually

fringence gives the cut gems a sleepy look due to doubling 2-3 carats are

Name:

among

Cut gems over

the rarest of collector items.

In allusion to the composition.

STICHTITE

Dimorph

STOLZITE

6

2

Crystallography:

1

Hexagonal

•

4H

2

0.

Dimorphous with

Lilac to rose pink.

Tetragonal; crystals tabular and thick,

Crystallography:

White

Luster:

Pearly, waxy, greasy.

Density:

2.

striated.

Brown, yellowish brown, fawn beige, tan, low red, red, greenish.

yel-

Resinous to subadamantine.

Hardness: Density:

2.5-3.

7.9-8.34.

Cleavage:

Indistinct; fracture

to lilac.

Optics:

Hardness:

commonly

Colors:

brittle.

Streak:

Raspite.

(R). Massive, foliated,

fibrous, lamellar, scaly.

Colors:

4.

or dipyramidal. Crystal faces

of Barbertonite.

Cr (C0 )(OH),6

PbW0

Formula:

Luster:

Mg

Formula:

After Robert Sticht of Tasmania, general man-

ager of the Mt. Lyell Mining and Railway Co.

can

more heav-

included, as well as strongly birefringent. This bire-

of back facets as seen through the table.

somewhat

USSR referred

o

=

2.27: e

=

2.19.

Uniaxial (— ).

1.5-2.5; greasy feel.

Birefringence:

16 (Quebec); 2.22 (South Africa).

Pleochroism:

0.08.

Not reported.

conchoidal to uneven;

STRENGITE

182

Not diagnostic.

Spectral:

None

Luminescence:

reported. in

the oxidation zone

of tungsten-hearing ore deposits.

Broken

Wales, Australia.

Stolzite

Strontianite

a rare mineral

is

(much

and there

ally pale

England; Sardinia; Germany: Nigeria. Utah; Arizona; Massachusetts; Pennsylvania.

Brazil:

Stone Sizes:

Comments:

The maximum

is

is

size

a collector's oddity, with

recommend

spectacular properties to

New South

Hill.

Austria.

is

about 2-4 carats, but an occasional larger stone might be encountered.

A secondary mineral

Occurrence:

Germany and

especially

fire;

little

it.

no

Colors are usu-

addition, the high

in

birefringence doubles back facets and

kills

the brilliance

of the stone. Cut strontianites are, however, decidedly rarer than

wulfenite) and usually occurs in very minute crystals.

However, the Australian crystals may be up to inch in size, and tiny transparent areas have yielded very small cut stones of a bright orange color.

uncommon and worth Name:

From

was

found.

pursuing for their scarcity value.

the town

Scotland where the mineral

in

1

Name:

After Dr. Stolz of

Bohemia who

first

SUCCINITE

See: Amber.

called

SUGILITE

attention to the mineral.

STRENGITE

first

Formula:

See: Variscite.

(K,Na)(Na,Fe

nite

Aragonite Group. Series to Arago-

in

tapering crystals

in

)Si 20.1o I

+ Mn.

Vitreous.

Luster:

sprays and fans; massive, granular.

Hardness: Density:

greenish, reddish.

6-6.5.

Optics:

Hardness: Density:

None; massive material tough.

=

o

1.590, Africa: o

3.63-3.785, depending on Sr content (vs. Ca). Perfect

1

direction. Fracture uneven. Brittle.

a = 1.52; p = (-),2V= 7°.

Birefringence:

1.66;

y =

In

SW

Occurrence:

1.606).

0.003-0.005.

Birefringence:

Not reported.

Luminescence:

and LW, may be white,

in

olive

in X-rays.

A low-temperature mineral, in veins, geodes,

granite. Later

these with

at 4110;

None.

Originally reported from Iwagi

Occurrence: west Japan,

green, bluish green, with phosphorescence. Both fluores-

cent and phosphorescent

=

1.595; e =

Strong band at 4190, weak band broad diffuse band centered at 5700.

Not diagnostic.

Luminescence:

1.610; e

=

Spectral:

0.150.

0.008-0.028.

Dispersion:

=

1.607 (India: o

Uniaxial (— ).

Pleochroism:

1.67.

=

1.610; e

3.5.

Cleavage:

Spectral:

2.74 (variable).

Cleavage:

Vitreous to resinous.

Luster:

Biaxial

-

Colorless, white, gray, yellowish, yellowish brown,

Colors:

Optics:

+,

dish violet (manganiferous), purplish, dark rose-red.

Orthorhombic. Crystals prismatic, often

Crystallography:

Fe

Light brownish yellow; lavender, intense red-

Colors:

SrCOi.

) 2 (Li 2

massive.

(CaCO,), Witherite (BaCO.O.

Formula:

-

Hexagonal; occurs as subhedral grains;

Crystallography:

STRONTIANITE

+1

Islet,

South-

an aegirine syenite mass within a biotite

occurrences were noted

manganese content

rich amethystine coloration.

bles sogdianite, but sugilite

in

India and Africa,

sufficient to

The mineral

produce a

closely resem-

does not contain Ti and Zr,

marls, and sulfide veins.

therefore chemical analyses will distinguish these two

San Bernardino County. California; Schoharie, New York; Ohio; New Mexico; Texas; Louisiana; South Dakota;

minerals.

Washington.

Africa.

Scotland; Mexico; India; Austria.

Madhya

Carleton County, Ontario, Canada; British Columbia,

Canada; Germany: major deposits. Pennsylvania: small crystals.

Very small faceted gems have been cut from small, pale-colored crystals from various localities, Stone Sizes:

Wessels Mine.

Kuruman

district,

near Hotazel, South

Pradesh, India.

Comments:

The Japanese

yellowish crystals and was

first

material occurs as tiny

discovered

in 1944.

Then,

in 1955, dark pink prismatic crystals identified as sugilite

were found in a few samples of manganese ore from what was then known as India's Central Province. Cuttable

SUNSTONE was not known until 1975, when a thin seam of was found in a core-drill sample in a manganese mine 14 miles northwest of Hotazel, in the Kuruman manganese fields of South Africa. The material occurred in low-grade ore, so mining proceeded in a different direction until 1979-1980, when the lower-grade ore was explored. A huge mass, as much as 10-12 tons, of sugilite was discovered at a depth of 3,200 feet. Only half of this material had the fine grape-jelly color associated with the gem variety, and of this, a tiny percentage (perhaps 0.1%) is translucent. The names Royal Lavulite, Royal Azel and Cybeline have been used in marketing the material. A commercial reserve sufficient for marketing

a

sugilite

Optics:

the material

2V=68°.

Wessels Mine.

exists in the

Name: ogist

After Professor Ken-ichi Sugi, the Japanese penol-

who

first

SULFUR

Alpha modification.

Formula:

S

Se.

Crystallography:

Dispersion:

=

2.038;

y =

2.245. Biaxial

Orthorhombic. Crystals tabular and

Yellow, yellowish brown, yellowish gray, red-

dish, greenish.

Luster:

White.

Resinous to greasy.

Distinct in shades of yellow.

Not diagnostic.

Spectral:

Luminescence: Occurrence:

None.

Sulfur

als as sulfides;

it

is

usually in combination with met-

occurs

in

native form in volcanic

Hardness: Cleavage: brittle.

and

hot spring areas (deposited from vapor); sedimentary rocks, and in huge quantities at salt domes.

Wyoming; Nevada;

California.

Chile; Mexico. Girgenti. Sicily: fine, large crystals.

Cianciana, Sicily; good crystals.

Louisiana and Texas;

salt

domes.

Stone Sizes: Transparent crystals exist that could yield stones over 50 carats, but these are specimens and not for

Broken

Comments:

2.05-2.09. 1.5-2.5.

been faceted.

crystals have occasionally

Sulfur has no use as a gem.

It is

so heat

hand may crack due to dropped from a height of sev-

sensitive that a crystal held in the

thermal shock. eral inches

difficult,

A

crystal

would most

likely

chip or crack — not ideal

some

is

is

in

fashioning stones of small

actually not very

common,

so cut

size.

An

ancient

name

for this mineral.

Imperfect. Fracture conchoidal. Sectile. Very

SUNSTONE

See: Feldspar.

who

Facetable

gems do have

scarcity value.

Name:

enormously

but the challenge has been met by cutters

have succeeded sulfur

Density:

+ ),

0.155.

properties for jewelry stones! Cutting sulfur

Streak:

(

0.291.

Pleochroism:

cutting.

pyramidal, often well formed; massive; powdery. Colors:

Birefringence:

/J

discovered the mineral.

Royal Lavulite is named after the lavender color, Royal Azel from the locality, Hotazel.

+

1.958;

183

TAAFEITE

China: reported

BeMg,Al 8 0, 6 +

Formula:

Fe,

Mn, Zn,

ince (o V, Cr.

=

Burma:

=

in

1.747; e

(o

=

dolomitized limestone

=

in

1.741; birefringence

=

1.720; e

=

Hunan

Prov-

0.006).

1.716; birefringence

=

0.004;

Crystallography:

Hexagonal; crystals microscopic, prismatic; known chiefly as rounded pebbles and cut

S.G.

gemstones.

Lanka: assumed origin of most known cut gems. Note: Polytype of taaffeite discovered in the Musgrave Ranges, Central Australia (o = 1.739; e = 1.735; S.G. =

Colors:

USSR:

3.59).

(o

=

1.735; e

=

1.726; birefringence

=

0.009).

Sri

Colorless, greenish, pinkish, lilac to purple,

bluish, bluish violet, red.

3.68).

Luster:

Vitreous.

Hardness:

3.60-3.62; Zincian

Density:

=

o

=

1.721-1.724; e

=

=

1.730; e

—

1.717-1.720.

gem

discoverer.

Count Edward Charles Richard

of 0.55 carat. This was presented to the living in Dublin.

Taaffe, a

A

second

stone identified as taaffeite weighed 0.86 carats and

1.726; birefringence

=

is

now in the Geological Museum, London. A third taaffeite 0.004.

of 0.84 carats, identified at the Gemological Institute of

America laboratory

in

New York, resides in the SI collecgem of 5.34

tion along with a dark brownish-purple

Not reported.

Pleochroism:

was analyzed, and the remainder was

recut into a

Bohemian-Irish gemologist

0.004-0.009.

Birefringence:

The originally discovered taaffeite came mauve spinels and weighed 1.419 carats;

part of this stone

Uniaxial. (— ).

Zincian: o

lot of

3.71.

Not reported.

Cleavage: Optics:

Stone Sizes: out of a

8-8.5.

Many other stones have been identified, perhaps many as 50. A Sri Lankan collector owns a flawless mauve oval weighing 13.22 carats. A 10.13 carat graymauve oval, lightly included, resides in another private carats.

Not diagnostic; however, the spectra of gem taaffeites are similar to those of red and blue-violet spinels containing Fe and Cr.

Spectral:

Luminescence: Inclusions:

Distinct green in

UV

Inclusions reported in Sri

as

collection, as well as a pink oval of 11.24 carats

and X-rays.

Lankan

numerous smaller stones. A Burmese taaffeite carats, also pale mauve, has been reported.

taaffeites

include: phlogopite; garnet; muscovite; apatite; spinel; zircon; fingerprints of negative crystals partly healed liquid fractures. to

The

and

spinels;

Comments:

and

like

apatite crystals tend

negative crystals, and fingerprints are

In

commonly

metamorphosed limestones and

its

birefringence. Additional stones will

undoubtedly be discovered

in

the future (generally

misidentified as spinel) as collectors search for these

observed.

Occurrence:

Taaffeite reacts to most gemological tests mauve-colored spinel, but can be distinguished on

the basis of

be well-formed prisms, colorless to yellow. The apa-

tites,

and

of 3.04

rarities. Taaffeite is one of the rarest of mineral species, and surely among the very rarest and most desirable of

skarns;

also as rolled pebbles, very rarely (China) in crystals

all

collector gemstones.

A

(microscopic).

184

zincian taaffeite with

ZnO

as high as

4.66% has

TANTALITE been reported. The material is reddish violet due to Mn and Cr and has higher refractive indices and S.G. than normal taaffeite. A red gemstone (1.02 carats) was reported from Sri Lanka with the following properties: R.I. = 1.717-1.721, birefringence

=

=

0.004, S.G.

3.61, hardness

= 8+,

hex-

agonal, slight reddish luminescence, Cr present (emis-

was first thought to be considered a new species and named taprobanite (after Taprobane, ancient name of the island of Sri Lanka). This material was eventually proven to be sion line in spectrum). This taaffeite, later

a taaffeite after all, and the name taprobanite has been dropped from use. However, the intense research into this problem led to a revised formula for taaffeite.

Comments: due

to several

may be

Massive

after other minerals.

slightly is

harder than

taic,

pseudomorphous easy to carve and is

often

talc

is

widely used for this purpose.

Name: name of

from the Arabic word talk or talq, the is from the Latin steads, a type of stone, derived from the Greek word steatos, meaning fat. Talc

is

the mineral. Steatite

TANTALITE

Series to Columbite: (Fe,Mn)(Nb,Ta) 2

(Fe,Mn)(Ta,Nb) 2

6.

6.

Orthorhombic. Crystals tabular

Crystallography:

stone in 1945.

first

Steatite

to impurities. Talc itself

After Count Taaffe, Bohemian-Irish gemologist,

discovered the

up

pounds.

Formula:

Name:

who

sive pieces that will yield large carvings,

185

pris-

matic, in aggregates, massive, compact.

TALC

MgjSi 4 Oio(OH)

Formula:

to

1

cm;

triclinic.

Tabular crystals

Streak:

Black, brownish black, reddish brown.

Luster:

Submetallic to vitreous.

usually massive, foliated, fine grained, compact.

Hardness: Colors:

may

tarnish iridescent.

.

Monoclinic,

Crystallography:

up

2

Black, brownish black, reddish brown;

Colors:

SOAPSTONE = STEATITE)

(=

6-6.5.

Pale green, dark green, greenish gray, white,

gray, silvery white, brownish.

Colors are due to impurities.

Density:

8.2;

decreases with Ta content (columbite,

5.2).

Luster:

Greasy, pearly, dull. Cleavage:

Hardness:

1

;

greasy

Distinct

1

direction. Fracture uneven. Brittle.

feel.

a = 2.26; f> = 2.30-2.40; y = 2.43. + ), 2 KLarge. Usually opaque, indices measured on powders or thin splinters. Optics:

Density:

2.20-2.83.

Biaxial

Cleavage:

Perfect

1

direction. Flexible

and

elastic

lamellae. Sectile.

Optics:

y=

(

Birefringence:

=

Monoclinic: a

1.539-1.550;

/3

=

1.589-1.594;

Pleochroism:

0.

1

60.

Strong; brown/red-brown.

1.589-1.600.

Triclinic:

a =

1.545;

2V =

Biaxial (— ),

Shadow edge

=

1.584; in

y =

Not diagnostic.

Spectral:

1.584.

monoclinic.

Luminescence:

None.

at 1.54.

Monoclinic: 0.050.

Birefringence: Spectral:

/J

0-30°

Triclinic: 0.039.

Not diagnostic.

Luminescence:

Usually none.

Some

is

pinkish

in

LW

Occurrence: In granite pegmatites. Colorado; Wyoming: New England. Canada; Brazil; Madagascar; France; Sweden; Finland: USSR; Zimbabwe; Western Australia. South Dakota: various localities.

(Silver Kale, California).

California: various localities.

Occurrence:

In hydrothermally altered ultrabasic rocks

and thermally altered siliceous dolomites. Worldwide occurrence, sometimes in large beds, often associated with serpentines.

Many localities in the United States, especially Vermont, New Hampshire, Massachusetts, Virginia, North Carolina. Georgia, California.

Lake Nyasa, Central Africa: India: China: Australia: Zimbabwe: Canada: USSR. Egypt: ancient deposit.

Very large crystals weighing many pounds The material is usually dark colored, opaque, and of interest only for cabochons. Stone Sizes:

have been found.

Comments:

Steatite

and soapstone are known

in

mas-

Tantalite

is

too dark to be of use as a

is

desired size.

Name: it

Stone Sizes:

gem

sometimes cut as a collector curiosity, but either faceted or in cabochons. These could be of any faceted

is

After the mythical character Tantalus, because

difficult to dissolve the

analysis.

mineral in acids prior to

TANZANITE

186

TANZTANITE

other tektites from the United States have been cut as curiosities, mostly small. The refractive index of a tektite

See: Epidote.

TEKTITE

seems

Formula:

Silica

(75%) + Al, Fe, Ca, Na, K, Mg, Ti, Mn.

Amorphous — a

Crystallography:

glass.

Black, green, greenish brown, brown in molda-

Colors:

other tektites black, colorless to brown; usually

vites;

opaque.

Comments:

Tektites were first discovered in 1787 in Czechoslovakia (then Moravia) near the River Moldau, hence the name moldavite. It has been argued that tektites

the

originated as a result of violent explosive activity on

Moon and

were thrown all the way to the Earth's Other scientists, currently in the majority, argue

surface.

that tektites are of terrestrial origin.

Vitreous.

Luster:

to vary (positively) with iron content.

debated Hardness:

5.5-6.5.

None. Fracture conchoidal.

Cleavage: Optics:

Isotropic;

N=

Inclusions: Often see numerous rounded or torpedoshaped bubbles; also swirl striae that are unlike those seen in paste (glass used to imitate gemstones). in

being

TEPHROITE

1.46-1.54.

Not diagnostic. Moldavites may show two vague bands in the blue and orange.

None

is

Brittle.

Mn

Formula:

Spectral:

Luminescence:

issue

Name: Moldavite is from the River Moldau; other tektite names are from the localities where they occur.

2.21-2.96 (see table).

Density:

The

in a lively way.

UV. Yellow-green

2

Si0 4

Crystallography:

commonly

gated;

.

Orthorhombic; crystals prismatic, elonmassive, compact, as disseminated

grains.

Reddish brown, salmony pink, blue-green, olive

Colors:

green gray. ,

in X-rays.

Streak: pale gray.

Occurrence:

Tektites occur worldwide in fields in

which

the glass bits are literally strewn over the ground, covering a very

wide area (see

Hardness:

table).

Faceted gems are usually cut from moldabecause the color of these tektites is lighter than

Stone Sizes: vites

Vitreous to greasy.

Luster:

most others. The color is a bottle green resembling diopside, and gems up to about 25 carats have been cut, although very large moldavites have been found. Various

Density:

6.

4.11.

Distinct; fracture conchoidal, uneven; brittle.

Cleavage: Optics:

a=

1.770-1.788;

/?

= 1.807-1.810; y = 1.817-1.825.

Biaxial (— ).

Tektites

Maximum

Name Moldavite 3

Czechoslovakia

Australite a

Australia

Darwin glass

Tasmania

Javaite

Java

Billitonite

Billiton Island

Indochinite 3

(near Borneo) Indochina

Philippinite

Philippines,

(rizalite)

Ivory

Coast

especially Ivory

Refractive

Size

Density

235 grams 218 grams

2.38-246

Locality

2.27-3.40

1

48-1.54

— — —

2.75-2.96 2.43-2.45

1.50-1.52 1.47-1.48 1.509

2.46-251

1.51-1 53

3200 grams

—

2.40-2.44 2.44-2.45

—

2.40-2.51 2.21

Luzon

Coast

Color

Index

1

1

bottle

black,

green

brown edge

green, black black black

49-1.51 1.513

black black

.50-1.52

black

tektite

Libyan Desert Glass 3

Libya

4500 grams

Bediasite3

Gonzales County,

91

.3

grams

2.33-2.43

1.462 1

48-1.51

pale greenish yellow black

Texas

Georgia tektite 3 Massachusetts tektite a

3

Have been faceted

Georgia Martha's Vineyard,

Massachusetts

— —

2.33 2.33

1.485 1.485

light light

olive-green olive-green

THOMSONITE 0.037-0.047.

Birefringence:

Distinct: greenish blue/reddish/brownish

Pleochroism: red.

Mn lines should be observed.

Not reported, but

Spectral:

Occurrence:

In

iron-manganese ore deposits and

187

Comments: Massive thaumasite cuts interesting catseye cabochons, especially if it is chatoyant, but the effect is relatively weak. The mineral is rather soft but seems to harden after being exposed to air.

Name:

From

because of

Greek thaumasein

the

(to

be surprised)

rather unusual chemical composition.

its

associated skarns. California; Colorado.

Franklin and Sterling

New Jersey:

Hill,

THOMSONITE

cuttable.

England; Sweden; France; Japan. Tamworth, N.S.W.. Australia; small Mn deposits with massive tephroite streaks in rhodonite. This material is suitable for cabochons.

Zeolite Group.

NaCa

Formula:

2

Al 5 Si 5 O20

6H

2

0.

Orthorhombic. Crystals prismatic or compact, or in radial or

Crystallography:

and very

acicular,

•

rare; usually

fibrous aggregates.

Comments:

brown and barely translucent. However, it takes a good polish and is massive enough to make good cabochons. Only the New Jersey and Australian localities seem to have provided such material, however. Faceted gems are unknown. Tephroite

is

generally reddish

Colorless, white yellowish, pink, greenish, grayish.

Colors:

A

translucent green variety has been called lintonite.

Vitreous to pearly.

Luster:

Hardness:

Name:

From

the

Greek

tephros,

Density:

2.25-2.40.

Cleavage:

THAUMASITE 1

•

12H 0.

Biaxial

2

Hexagonal. Crystals acicular; usually

Crystallography: massive, compact.

Perfect

(

Shadow edge

Birefringence: Spectral:

Luster:

Vitreous, silky, greasy.

Luminescence:

Optics:

1.91.

Indistinct. Fracture subconchoidal. Brittle.

o

=

1.500-1.507; e

=

1.464-1.468.

Uniaxial (— ). Birefringence: Spectral:

1.518-1.544.

None. Pyroelectric. Patches of brown and white

in

LW.

Thomsonite is a secondary mineral in lavas and basic igneous rocks. Oregon; California; Colorado; New Jersey. Nova Scotia, Canada; Greenland; Ireland: Scotland: Italy; India; Czechoslovakia; Germany. Isle Royale, Michigan: patterned pebbles. Stockly Bay, Michigan: lintonite; also at Grand Marais, Cook County, Minnesota (Thomsonite Beach I.

0.036.

Not diagnostic.

White

Luminescence:

in

SW

(Paterson,

New

Jersey)

with phosphorescence.

Occurrence:

y=

Occurrence:

3.5.

Cleavage:

1.513-1.533;

0.021.

Colorless, white.

Density:

direction. Fracture uneven. Brittle.

at 1.52-1.54.

Colors:

Hardness:

1

a = 1.497-1.530; /J = + ),2V= 42-75°.

Optics:

Ca,Si(C0 )(S0 4 )(OH) 6

Formula:

5-5.5.

meaning ash colored.

Associated with zeolites;

in lime-rich

met-

Stone Sizes: Cabochons up to several inches in length have been cut from material recovered in Michigan at Isle Royale, the best known locality. Large pieces are not abundant, especially with good patterns. Faceted gems are exceedingly rare;

gems up

to 5 carats

from a German

have been reported to me.

amorphic rocks.

locality

Crestmore, California; Beaver County. Utah; Cochise

Comments: Thomsonite cabochons take a high polish but are somewhat brittle. These are especially lovely when a pinkish gray eyelike pattern is present, but such

County. Arizona. Paterson,

New Jersey:

fine crystals.

Centreville, Virginia: in masses.

Langban, Sweden. Stone Sizes: Found as relatively compact fibrous masses up to a few inches in size. Facetable material does not exist, but cabochons have been cut from some of the

more compact

material.

is rare. Lintonite, from Michigan, is translucent and green and is sometimes mistaken for jade. A faceted thomsonite must be considered a great rarity.

material

Name:

Thomsonite

chemist

who

after a

first

for

Thomas Thomson, the Scottish

analyzed the material. Lintonite

Miss Linton.

is

TIGER EYE

188

TIGEREYE

Usually planes of tiny liquid inclusions, each

Inclusions:

See: Quartz.

Some

containing a gas bubble.

TINZENITE

Not diagnostic. Heated pink gems contain and may show a Cr spectrum with a weak line at 6820. As in ruby, this line may reverse and become fluorescent.

Spectral:

TITANITE

See: Sphene.

Cr,

TOPAZ AhSiCMEOHh +

Formula:

Cr.

Orthorhombic. Crystals prismatic,

Crystallography:

stumpy, sometimes very large, often well formed; also massive, granular, as rolled pebbles. Colorless, white, gray, pale to

Colors:

three-phase inclusions

have been noted also.

See: Axinite.

medium

greenish, yellow, yellow-brown, orange, pale pink,

Luminescence: Blue and colorless: weak yellow-green in LW, weaker in SW, greenish white to violet-blue in X-rays, and gems turn brown due to irradiation. Sherry brown and pink: orange-yellow in LW, weaker in SW, sometimes greenish white in SW. This material fluoresces brownish yellow to orange in X-rays.

blue,

deep

Occurrence:

In pegmatites

and high-temperature quartz and rhyolite; in contact

veins; also in cavities in granite

pink, tan, beige, red.

zones; in alluvial deposits as pebbles. Vitreous.

Luster:

Hardness:

New Hampshire: Pike's

Cleavage:

crystals.

some

Texas: colorless and blue,

8.

Perfect basal

(

1

Peak area, Colorado:

facetable to large size.

fine blue crystals in granitic

direction). Fracture conchoi-

rocks; also colorless, reddish, yellow, dal. Brittle.

Dispersion:

Density:

and

Thomas Range, Utah:

is

a rough correlation between color

density, as follows: pin k: 3.50-3.53; yellow: 3.51-3.54;

Minas Gerais,

and density of topaz have been correlated with the ratio of (OH) to (OH + F) in

refractive indices

linearly

the formula.

Brazil: fine yellow to

orange crystals,

facetable to large size; also colorless and pale yellow crystals

colorless: 3.56-3.57; blue: 3.56-3.57.

The

facetable.

tals in rhyolite; facetable.

0.014.

There

some

sherry-colored terminated crys-

up

to several

hundred pounds

in size,

mostly

transparent; pale blue crystals and rolled pebbles,

much

Cr and when heated (burned) turn pink and show a Cr spectrum. Such

facetable;

some orange

crystals contain

Pale blue: bright blue/pale rose/colorless.

may be distinctly reddish even before heating. Mardan, Pakistan: fine pink crystals, terminated, cuttable, in limestone matrix, at Ghundao Hill, near Katlang. San Luis Potosi, Mexico: fine brownish to sherry-colored

Dark

crystals; also colorless,

material

Pleochroism:

Dark yellow:

Varies with color of material: citron yellow/honey yellow/straw yellow.

rose red.

many excellent forms, cuttable, some yellowish; can be darkened by irradiation but color

Rose-pink: yellow/purple/lilac.

fades in sunlight.

rose-red: red to dark red/yellow to

honey yellow/

Red-brown: reddish/reddish/yellow. "Burned" pink: rose/rose/colorless. Brown: yellow-brown/yellow-brown/weak yellow-brown. Green: colorless to blue-green/green to bright blue-green/ colorless to bright green.

Urals,

USSR: fine blue crystals, often

cuttable; also green,

magenta colors (gemmy) and pinks from Sanarka. Jos, Nigeria: fine blue crystals, also white,

Madagascar: various colors

in crystals

many cuttable.

and pebbles, often

cuttable.

Birefrin-

Locality

USSR

1.609

—

1.619

gence

Density

0.010

3.53

Color bluish

Comments F-rich

pale yellow

Ouro

Preto, Brazil

1.629

1.631

1.637

0008

3.53

brownish

rich in

(OH]

Cr

Thomas Range,

1.607

1.610

1.629 1.610 1.610

1.632 1.613

1.618

0.011

356

sherry

649

3.52 3.56 3.56

rose-pink

3.53

faint

Utah Katlang, Pakistan Katlang, Pakistan Tarryall

Mountains,

—

1

620

0.010 0.009 0.010

—

1.627

0.008

1

1.619

brownish blue

Colorado Schneckenstein,

Saxony Germany

1.619

yellow

contains Cr

TOURMALINE GROUP Sri

Lanka and Burma: from the gem

gravels, colorless,

and blue gemmy masses. Queensland and Tasmania, Australia: blue, colorless and brownish gem crystals. Tingha, New South Wales, Australia: green, gemmy. Klein Spitzkopje, Namibia: colorless and blue crystals from pegmatites, gemmy. Zimbabwe: Cornwall, England: Scotland: Japan: crystals and pebbles. yellow,

and no detection test exists for the irradiation treatment. A very dark blue topaz should have its origin questioned if

sold at a very high price, since this color in nature

would be a great rarity. Treated blue topaz has become one of the most popular and abundant materials in the gemstone marketplace.

Name:

Topaz may derive from the Sanskrit word

comes from

called topazos,

Crystals of topaz may weigh hundreds of pounds and are often quite gemmy at this size. Gems up to 20,000 carats have been cut from material of various colors. Museums seem to delight in obtaining monstersized topaz gems for display. Pink gems over 5 carats (Pakistan) are rare, however, and a Brazilian deep orange gem weighing more than 20 carats is considered large.

the

name

meaning

tapas,

orange color; alternatively,

meaning/i'/ie, in allusion to the it

Schneckenstein, Germany: faint yellow, gemmy.

189

of the island in the

Red Sea

to seek.

Stone Sizes:

known pink topaz is an oval of 79+ carats, USSR. The largest Brazilian topaz crystal ever

The

largest

from the found of an orange color ("precious topaz") reportedly measured 5 X 27 cm and weighed nearly 2 kg. A very fine lot (9 cuttable crystals) found in the 1960s weighed over 900 grams and yielded several superb gems, one weighing more than 100 carats and several over 50 carats. The gem giants exist in blue, colorless, and pale yellow colors. Red topaz from the tips of some Brazilian crystals is exceedingly rare, the largest about 70 carats. SI: 7725 (yellow, Brazil); 3273 (blue, Brazil); 2680 (colorless, Brazil);

1469 (yellow-green, Brazil); 1300 (sherry,

398 (pale blue, USSR); 325 (colorless, Colorado); 170.8 (champagne, Madagascar); Brazil);

685 (pale blue,

Brazil);

146.4 (pale blue, Texas); 93.6 (orange, Brazil); 50.8 (col-

34 (deep pink, Brazil); 24.4 (blue.

orless, Japan);

New

Hampshire); 17 (blue, California).

AMNH:

TOPAZOLITE

See: Garnet.

TOURMALINE GROUP name

Tourmaline

is

minerals,

having essentially the same crystal structure

all

a

but varying widely properties.

in

applied to a family of related

chemical composition, color, and

The nomenclature of tourmalines is complex

because there are nine distinct mineral species in the group, as well as a wide variety of names that have been applied to specific color varieties. Tourmaline crystals are abundant worldwide, are sometimes large and well terminated, and often are cuttable. Formulas: Dravite: Uvite:

NaMg.AUB^O^OHblOHT) CaMgMUMglBjSi^OHMOHT)

Na(Fe,Mn) Al 6 B Si60 7(OH) 3 (OH,F) Na(Li,AlhAl6B 3 Si6027(OH) 3 (OH,F) Liddicoatite: Ca(Li,Al) 3 Al 5 B Si 6 027(OH) (OH,F) Schorl:

1

2

1

Elbaite:

3

3

NaFe 3 Al 6 B 3 Si603oF Chromdravite: NaMg 3 Cr6 (B0 3

)

Tsilaisite:

)

Buergerite:

3 Si 6 18 (OH) 4 Na(Mn,Al) 3 Al6(B0 3 3 Si60 18 (0,OH,F)4 + + Ferridravite: (Na,K)(Mg,Fe 3 Fe 6 '(BOjhSisOm (0,OH) 4 -')

71 (red, Brazil); 308 (pale blue, Brazil); 258 (deep blue, Brazil); 1463 (deep blue, egg-shaped, Brazil);

Crystallography:

241 (pale orange-brown, Burma).

mon,

BM:

various terminations; also equant, acicular.

137 pounds (crystal, Norway); 1300 (colorless, Bra614 (blue, Brazil). ROM: 3000 (blue, Brazil); 365 (pale brown, Burma). LA: 1800 grams (orange crystal, Brazil). zil);

NMC:

Colors:

(trigonal). Crystals

Tourmalines come

(light blue, treated,

largest faceted

emerald-cut, reputedly the world's

gemstone called The Brazilian Princess);

(pink oval,

USSR,

world's largest this color but not

flawless); 58.8 (pink oval,

Comments:

USSR,

flawless).

Topaz is a popular and durable gem, occurwide range of colors. The rarest colors are natural pink, from the USSR, Pakistan, and (rarely) Brazil; red; and fine golden orange, sometimes with a pink tone. Colorless topaz can, through irradiation plus heat treatment, be turned a deep blue color unknown in natural topaz. This is often sold on the market as a substitute for the much higher-priced dark aquamarine, ring in a

from colorless zoned along their and so forth) or con-

in all colors

length (bicolor, tricolor, particolor, centrically (blue, Texas); 7,033 (dark blue, treated); 21,327

com-

to black. Crystals are frequently color

498.61 (light blue, untreated, Brazil).

PC: 173

~79

Hexagonal

usually long prismatic, heavily striated along length,

zoned (watermelon tourmaline). Dravite

usually black to brown,

may be

colorless. Uvite

is

is

black,

brown, and green, usually dark colors. Schorl tends to be black, blue, or blue-green. Buergerite is always dark brown to black, with a bronze-colored iridescence or Schiller under the crystal surface. The gem tourmaline. elbaite, occurs in a huge range of colors and shades. Liddicoatite is a relatively newly described species that was for years considered to be elbaite (from Madagascar) but when investigated turned out to be a calcium analog of elbaite. Chromdravite, as might be expected, is an intense dark green color from the USSR. Gemmy, bright yellow manganiferous elbaite, close to tsilaisite in composition, has been found in Zambia.

.

7

TOURMALINE GROUP

90

Properties in Tourmaline

Species

e

Birefringence

0.016-0.032 0.017-0.021 0.016-0.046 0.013-0.024 0.023-0.028 0.016 0.065-0.080 0.057 0.006

1.627-1.675 1.632-1.660

1.604-1.643

Uvite

Schorl

1.638-1 698

Elbaite

1.619-1.655 1.645-1.648 1.637 1.735 1.80-1.82 1.778

1.620-1.675 1.603-1.634

Dravite

Tsilaisite

Liddicoatite

Buergerite Ferridravite

Chromdravite

Group

1.612-1 .639

1.622-1 623 1.621

1.655-1.670 1.743 1.772

Density [range]

Pink and red: 3.01-3,06. Pale green: 3.05.

Hardness: Spectral:

3.13 3.05 3.13

302

3.29-3.32 3.18-3.33

326

3.39-341

3.40

3.30

Differentiated according to tourmaline color

Density:

Brown:

3.06.

3.08-3.

1

1

Blue: 3.05-3.11.

Not diagnostic; usually weak spectra observed.

Dispersion:

2.82-324

(approximate values):

Dark green:

7-7.5.

3 10

304

— —

referred to as indicolite.

Vitreous.

3.90-3.29

301-309 2.84-3.10

Certain color varieties of tourmaline have widely used names. Achroite is colorless tourmaline; rubellite refers to pink and red shades, and blue tourmaline is generally

Luster:

Density (average)

Yellow-orange: 3.10.

Black: 3.11-3.12.

0.017

Tourmaline displays elongated or threadlike sometimes with two-phase inclusions. The tubes

Inclusions:

Pleochroism: line

is

The absorption

of the o-ray in tourma-

strong enough to plane-polarize

light.

Sometimes

absorbed and a tourmaline may appear to be isotropic because it shows only one absorption edge on the refractometer. Pleochroism is especially strong in dark green and brown tourmalines. Pale colors have weak dichroism. Light traveling along the length of a prismatic crystal always shows a deeper color than at this ray is totally

right angles to this direction.

cavities,

usually run parallel to the length of crystals and,

densely packed,

may produce

gems

yields catseye

filled fractures in

reflect light

when

a chatoyant effect that

cabochons. There may be gas-

in

red tourmalines; also

flat films that

and appear black. Also: hornblende; mica

crystals; apatite; zircon.

Tourmalines are usually weak to

Luminescence:

inert

Typical Pleochroic Colors for Tourmaline Species

Specimen

o

Buergerite

yellow-brown

Dravite

yellow

very pale yellow colorless pale yellow

orange-yellow dark green bluish green medium to dark brown Elbaite

medium

yellowish green yellowish to light brown light pink or colorless yellow to olive green light green to purplish colorless to pink to purple

pink

green blue-green blue Ferridravite

dark brown

Liddicoatite (like elbaite but type

Schorl

to

dark

olive

specimen

green

olive

is

green dark brown

green brown)

light olive light

to light

brown

blue to greenish blue

yellow, yellow-brown, pale violet, or colorless

green-brown dark brown

yellow, light

dark green yellow-brown

yellow-green intense yellow

rose-yellow

brown, or yellowish blue-green

Uvite (like dravite)

Chromdravite Tsilaisite

Source: From R V. Dietrich. The Tourmaline Group, Van Nostrand Reinhold, Reinhold Company Inc.

New

York,

1

985, p

1

44: copyright

e

1

985 by Van Nostrand

TOURMALINE GROUP

UV light. Stones may be chalky blue to strong blue in SW (Newry, Maine). Pink gems from Brazil may be blue in

SW, and gems from Tanzania (golden brown and green stones) are strong yellow in SW.

or lavender in yellow,

Connecticut: At Haddam, elbaite

Occurrence: Tourmaline occurs in crystalline schists; in granites and granite pegmatities (especially elbaite); in gneiss, marbles and other contact metamorphic rocks (especially dravite, uvite). Tourmaline is also found as inclusions in quartz. Sri

Lanka: Yellow and brown

source of

gem

tourmaline,

both fine crystals and gemmy material. The pink from here is a unique pastel shade. Maine: At Newry, huge deposit of fine elbaite, with exquisite gem material in green, blue-green, blue, and ities, in

elbaite

pink to red colors.

Uniaxial (— ). See table.

Optics:

crystals; this

now known

to

is

the original

be uvite rather

in

small but fine crys-

color-zoned.

tals,

Mexico: Buergerite occurs in rhyolite at San Luis Potosi. York; New Jersey: At Franklin, and Hamburg, New Jersey, and at Gouverneur and DeKalb, New York, uvite crystals, some with gem potential. This material had always been regarded as dravite. Zambia: At Chipata, dark red crystals similar to Kenyan

New

than dravite.

dravite. Indices 1.624-1.654; birefringence

Burma: The Mogok area produces red tourmalines, also some pink elbaites and brown uvites. Mursinka, Urals, USSR: also at Nerchinsk, blue, red, and violet crystals in a decomposed granite. Central Karelia, USSR: chromdravite (dark green). Brazil: In Minas Gerais and other states, usually elbaite, in a huge variety of colors and sometimes large crystals;

S.G.

watermelon tourmaline. Especially noteworthy are the immense cranberry-red crystals from the Jonas Lima Mine and the superb dark red material from Ouro Fino. also bicolor, catseye,

Kashmir, India: Green elbaite crystals (refractive indices 1.643, 1.622; S.G. 3.05, birefringence 0.021).

Nuristan, Afghanistan: superb

gem

elbaite in shades of

=

3.03-3.07 (average 3.05). Also

Usakos, Namibia: Fine elbaite of rich green color (chrome

MnO up to 9.2%, very rare. There are many other tourmaline localities, but the above are the major gem-producing ones. Stone Sizes: Tourmalines weighing hundreds of carats have been cut out of material from various localities.

and Mozambique produce some of the largest Maine and California crystals of very large size have been discovered. Most larger museums have fine tourmaline collections and display very large gems. A representative collection of tourmaline colors would have to encompass well over 100 stones. Brazil

stones, but

SI: 246 (pink, faceted egg, California); 116.2, 100 (pink,

Klein Spitzkopje, Otavi, Namibia: Tourmaline

many

in

shades of green and other colors (elbaite). Zimbabwe: In the Somabula Forest area, fine elbaite.

Mozambique: At Alta Ligonha, pale-colored

Brazil); 18.4

60 (blue-green, Brazil); 41.6 (brown, Sri Lanka); 23.5 (pale brown, Brazil); 17.9 (green. South Africa); 17.7 (yellow-green, Elba, Italy).

elbaite in

PC: 258.08 (green catseye 256 (green Maine — very large )

various shades; bicolors.

Madagascar: Liddicoatite (previously thought to be elbaite) in a huge range of colors, shades; crystals often concen-

zoned with many color zones, triangular

in out-

crystals very large. Also fine rubellite.

Tanzania: Elbaite containing Cr and V, resulting

in rich

green shades. is

dra-

;

,

for locality).

Comments: Tourmaline is one of the most popular of gems among collectors because it is usually inexpensive and occurs in a vast array of colors. The colors are due to an almost unbelievable complexity of chemical composition, to

Kenya: Fine, deep red and other colors; the red vite; (also

(champagne color, Mozambique); Mozambique); 117, 110 (green, Brazil); USSR); 75 (rose-red, Brazil); 62.4 (pink, (pink, Maine); 103.8 (rose, Mozambique);

122.9 (green,

110.8 (pink,

many

which John Ruskins quip (1890)

"the chemistry of (tourmaline] doctor's prescription than the

yellow shades).

still

was used

ing jewelry during the Victorian era, a practice Birefrin-

1.654 1.657 1.642

S.G.

Color

0.031 0.031

3.07 3.08 3.04

red red yellow

to several

cm, suitable for cutting. abundance at Pa la and other

California: Elbaite in

mournused

Such material is seldom seen in jewelry at all in modern times. Tourmaline crystals are often cracked and flawed, which puts a premium on clean gemstones, especially those over about 10 carats in size.

only

cabochons. The eye

in

catseye tourmalines can be

very strong, set against a richly colored gem. Tourma-

occur in a wide enough range of colors to satisfy about any fashion requirement. There is no cleav-

lines

local-

The

acceptable type of inclusions are the tubes that, when densely packed, produce a chatoyancy and catseye effect in

Glenbuchat, Aberdeenshire, Scotland: color-zoned elbaite

up

in

little

today.

gence

0.022

applies:

more like a mediaeval making of a respectable is

mineral." Schorl, the black tourmaline,

Indices:

1.623 1.626 1.619

0.030;

gemmy

yellow material with

tourmaline).

line;

=

tsilaisite,

California); 172.7, 124.8

blue, pink, green, even emerald green.

trically

191

just

TRANSVAAL JADE

792

and the slight brittleness of the material is not a major problem in wear. Small tourmalines (under 5 carats) are fairly easy to obtain at modest cost. Very large, fine-colored stones are both rare and costly, however. age,

Names: Tourmaline is from the Singhalese word tummali, meaning mixed-colored stones because tourmalines were often confused with other gems. Dravite

is

named

the Carinthian district of Drave, Austria. Schorl

German mining term with ore. Elbaite is

named

is

after

an old

unwanted minerals associated

for

Hardness:

5-6.

2.9-3.2 (catseye

Density:

gem, Ontario,

2.98; hexagonite,

2.98-3.03).

Good

Cleavage:

2 directions. Fracture uneven. Brittle.

Variable with composition (see figure),

Optics:

a = 1.560-1.562;

=

{-),2V =

Biaxial

y = 1.624-1.643.

1.613;

81°.

Note: Tanzania, green crystals: 1.608-1.631, S.G. 3.02.

after the Isle of Elba, Italy. Buergerite

is

after Professor

Martin

pher and well-known research scientist. Liddicoatite is named after Richard T. Liddicoat, director of the Gemological Institute of America. Chromdravite is named for its composition. Uvite is named after the Sri Lankan locality.

TRANSVAAL JADE

0.017-0.027; hexagonite 0.019-0.028.

Birefringence:

Buerger, crystallogra-

J.

Hexagonite: bluish-red/deep rose/deep

Pleochroism: red-violet.

Tanzanian green crystals:

light yellowish green/light

green/green.

Not diagnostic. Some tremolite shows a line 4370 typical of jadeite. Chromiferous material may display chromium spectrum. Spectral:

See: Garnet.

at

TRAPICHE EMERALD

See: Feldspar

Luminescence:

TRAVERTINE

Hexagonite shows orange, medium pink

SW

greenish white in

TREMOLITE lite.

Variety: Hexagonite. Series to Actino-

Amphibole Group. See

Ca2Mg

Formula:

also: Jade, Nephrite.

bladed; fibrous, massive, granular.

White, colorless,

Luster:

Vitreous.

in contact and regionally magnesian limestones, and

Tremolite occurs

metamorphosed dolomites,

Monoclinic. Crystals prismatic or

Colors:

(Lee, Massachusetts) and dull

yellowish in LW.

Occurrence:

s Si 8 022(OH) 2 + Fe.

Crystallography:

LW, SW. Also, medium

to pinkish red fluorescence in

See: Calcite

in

in ultrabasic rocks.

California: Arizona: Utah: Colorado: Connecticut:

South

Dakota: Massachusetts.

gray, pale greenish, pink,

brown.

Italy: Switzerland; Austria.

New York: hexagonite, some cuttable; also at Edwards and Balmat, New York. Ontario and Quebec, Canada: gray, green and blue crysFowler,

tals;

a chatoyant greenish variety found in Ontario cuts

interesting catseye gems.

Burma: green catseye gems. 1

70

1

68

Lelatema. Tanzania: green facetable crystals up to 25

mm. deep green with Cr spec-

Sierra Leone: Cr-rich tremolite, 1

trum displayed.

66

S.G.

r^l

R.I. 1

1

64

r*

35

C[

- 34

62 s G.

1

60 Fer ro-

-Tren

100

dCll

90

Ca 2 Mg 5 Si 8

22

80

70

60

40

50

20

30

_

olite

—

100 Mg:(Mg + Fe

+2

+

Fe*

3

is

Fe 2

10

4

1.21

NMC:

New

catseye, Ontario); 12.55 (dark

York); 4.55 (dark blue

brown catseye, Ontario).

Fe 3 * +

Comments:

Adapted from W. A. Deer, R. A. Howie, and J. Zussman, 1962, The Rock Forming Minerals, vol. 2 (New York: Wiley),

taking

257.

in

(medium purple. New York).

1.39 (deep purple,

Mn).

p.

the 5-10 carat range.

Hexagonite is known in facetable material only from New York and these pieces yield gems to only about 1 carat. Chrome tremolite is also very rare and cut gems are tiny. Catseye hexagonites have also been cut.

1

is

Larger crystals exist but are usually badly fractured.

PC:

f

and cut gems are true collector

largest of these

3

30

+ Mn)

expressed as Mg/(Mg

The

items.

Refractive index and specific gravity variations with chemical composition in the tremolite-ferroactinolite series.

Composition

Small colorless and transparent tremolite

crystals are very rare,

33 32

CajFe^SigO^IOHIj

(OH) 2

Stone Sizes:

of the

it

It is

possible to misidentify tremolite, mis-

for other amphiboles.

gem

Hexagonite

varieties of tremolite.

If

is

the rarest

tremolite occurs in

very tiny fibrous crystals, densely matted and interlocked.

TUGTUPITE then known as nephrite (jade). Material containing more or less parallel fibers is somewhat chatoyant and yields weak catseyes. These are sometimes called catseye it is

been tested and are actually tremolite or

jades, but have (if

more

Name:

iron-rich) actinolite.

From

the Tremola Valley on the south side of

St. Gotthard, Switzerland. Hexagonite was so named because it was thought to be a hexagonal mineral when first

described.

Massachusetts: Maine: Pala, California.

Germany; Finland; Sweden; France;

See: Quartz.

TRIPHANE

See:

TSAVORITE

Li(Fe

+2 ,

Mn

f2

Series to Lithio-

Orthorhombic;

Crystallography:

and compact form. crystals prismatic, often

Colors:

White

Luster:

Vitreous to greasy.

compact.

Greenish gray, bluish gray; alters to brownish or blackish hues (lithiophilite is clove brown, yellowish brown, honey yellow, salmon). Colors:

Vitreous; resinous to subresinous.

Luster:

Hardness: Density:

(lithiophilite)

1:1)

=

3.52; density

Cleavage:

2.3-2.57.

Perfect

is

1

not linear with

Fe:Mn

May

Distinct. Fracture conchoidal. Brittle.

o

Optics:

Pure Fe end of series = 3.58, pure Mn = 3.34. The halfway point (Fe:Mn =

3.42.

Density:

Uniaxial

(

1

= fi

1

.689- 1 .695

;

y=

1

.695- 1 .702.

Pleochroism:

May sometimes

be observed optically

interference figures

(

)

and uniaxial

may be observed, depending on

Fe:Mn ratio. Refractive indices increase with Fe content but may be substantially decreased if Mg substitutes for (Fe,Mn).

Pleochroism:

0.006-0.008.

Spectral:

None

Occurrence:

As

a

SW.

SW, cerise

red,

and very intense; phosphoresces dull

medium cream

white.

material darkens in color

when exposed

to

UV light

and slowly bleaches. Veins

in

nepheline syenite pegmatite,

in

Tugtup. Illimaussaq, Greenland: from the Taseq and

reported. in granitic

pegma-

South Dakota: as enormous crystals up to 6

feet long.

New Hampshire:

Gener-

Greenland: SW, pastel orange-red; LW, bright

Occurrence: Greenland.

often altered to a wide array of secondary phosphates. Hills,

color.

than LW.

lithiophilite

greenish yellow/pale pink.

primary mineral

Very distinctive rose-red

SW

better reaction in

The

Not diagnostic.

Luminescence:

in

Kvanefjeld, Greenland: LW, bright orange to orangered to

Absent or very weak; some

may show deep pink/pale

redder

orange: phosphoresces bright cream or orange-cream,

red;

Birefringence:

Strong: bluish-red/orange-red.

Luminescence: Taseq,

the

1.502.

Not diagnostic.

Biaxial (+). ally

e=

0.006-0.008.

Birefringence:

ratio.

direction; fracture subconchoidal

.689- 1 .694;

1.496;

)

be anomalously biaxial with 2 V from 0° to 10°.

Spectral:

a=

=

+ or (— ).

to uneven.

Optics:

to pink, rose red, bluish, greenish; mottled.

4-6.5 reported.

Hardness:

Cleavage:

4-5.

end

Black

Tetragonal. Only occurs in massive

Crystallography:

with rounded faces, but very rare; usually massive, cleav-

tites,

See: Garnet.

Na4AlBeSi 4 0i2Cl.

Formula:

)P0 4 + Mg.

philite.

able,

threefold and family,

presence of three cations.

TUGTUPITE

TRIPHYLITE Formula:

From Greek words meaning

in allusion to the

Spodumene.

Brazil.

Stone Sizes: Large stones conceivably could be cut from some of the immense crystals found in South Dakota, but these are usually opaque or altered. Tiny brown stones have been cut from Brazilian material. This is the kind of mineral that could surprise the world of gem species collectors by appearing as cuttable crystals from a newly discovered deposit at almost any time.

Name:

TRIDYMITE

193

excellent crystals at Chandler's Mill,

Palermo, Grafton Center, North Groton.

Kvanefjeld areas. Also noted on the Kola Peninsula, USSR.

Only a few faceted gems have been cut, all very small, and not completely transparent. A typical gem size would be 1-2 carats. Translucent material can also be faceted but is usually cut into cabochons. DecoStone Sizes:

)

;

TURQUOISE

194

rative objects

was

tugtupite

were carved from some larger pieces when

Comments:

Tugtupite was discovered in I960 and has been used sporadically in jewelry. The material has a rich color and has been sought after by collectors of fluorescent minerals because of its intense reaction in UV. Tugtupite seems to have diminished in abundance and is somewhat hard to obtain, especially in cuttable pieces, and it seems that the material was quite scarce at the source locality. Clean faceted gems are great rarities.

Name:

After the locality. Tugtup

means reindeer, hence,

Series to Chalcosiderite.

CuAUPO^OH)* 5H •

turquoise

almost synonymous with material of the

is

Tibet: turquoise

green

China: some mines appear to have operated there

in

B.C. indicate the possibility

in

the

Wudang mountain

Province and also typically

Crystals blue. Massive materials dark blue to

pale blue, green, blue-green, apple green, grayish green. Crystals vitreous; massive,

waxy or dull, earthy.

ally

up

little

of a centuries-old exploiis

currently

mined

area of northwestern Hubei

Shaanxi Province about 150 km to compact nodules

material occurs as

cm, with much

larger masses occasion-

color ranges from pale blue to light

green.

Egypt: on the Sinai Peninsula, turquoise Serabit el

is

mined

at

Khddim and Mahardh. These mines operated

and the turquoise was used by the Pharaohs. The producing area extends along the Suez Gulf, where the material occurs in sandstone. Earth movements have brecciated the turquoise and matrix, and there is considerable limonite present. The color is

as early as 1000 B.C.,

5-6.

Crystals 2.84; massive in the range 2.6-2.9.

Density:

to 8

The

found.

in

The

crusts.

Hardness:

of this country, and is

the northwest.

Colors:

gem

the national

is

the most prized color. Very

material

is

tation of local deposits. Fine turquoise

microscopic; microcrystalline, massive; concretionary;

and

to a cutter,

exist (well

highest quality.

1300

+ Fe.

2

Triclinia Crystals extremely rare and

Crystallography:

Luster:

gems might

ancient times. Archaeological finds dated as early as

TURQUOISE

veins

one could be tempting

available today.

reindeer stone.

Formula:

and some very under 1 carat). Iran: the district of Nishapur, on Ali-mersai Mountain. Turquoise is found in porphyry and trachyte rocks, cemented by brown limonite. The color is uniform and a lovely sky blue, sometimes veined by thin lines of limonitic matrix. The blue is often very intense. The mines have been worked for centuries, and Persian (now Iranian) larger

tiny faceted

found.

first

Iran. 2.75-2.85;

United States. 2.6-2.7; China, 2.70;

some may fade

blue to greenish blue;

Eilat, Israel 2.56-2.70;

USSR: turquoise

Sinai Peninsula, 2.81

Chile: at the Tibet, 2.72;

is

in the sun.

reported from the Uzbek Republic.

Chuquicamata copper mine turquoise of is found. Not much has reached the

very fine color

Bahia. Brazil. 2.40-2.65.

marketplace.

None

Cleavage:

in

massive material. Fracture even,

sometimes conchoidal.

been found

Massive material gives shadow edge

Optics:

I

mean

refrac-

a = 1.61; p* = + ), 2 V= 40°.

Biaxial

(

1.62;

y =

compact turquoise

in large deposits.

a high polish,

tive index) of 1.62.

Crystals:

Australia: dense,

and

is

of fine color has

This material

uniform

in color.

is

solid, takes

The nodules

in

occurs may reach a size of hundreds of pounds. The material has a slight tendency to shear along planes

which

it

1.65.

of weakness.

The color resembles that of Persian

(Iranian

turquoise.

Birefringence:

Pleochroism: Spectral:

0.040.

Weak: colorless/pale blue or pale green.

can be

4320— these

4600 (vague) and reflected from the

distinctive; lines at

are usually seen in light

turquoise surface.

Luminescence: SW and X-rays.

Greenish yellow to blue

in

LW,

Mexico: some turquoise has been reported from Zacatecas. Pan a Pique. Bahia. Brazil: Porous and cryptocrystalline material, R.I. - 1.618.

United States: there are many turquoise localities in the United States. Connoisseurs can tell the actual mine of origin of many cut gemstones because of distinctive

nuances inert in

Occurrence: Turquoise is formed by the action of percolating groundwaters in aluminous rocks where Cu is present, as in the vicinity of copper deposits. Lynch Station. Virginia: the only well known occurrence of crystals. These are microscopic, but an occasional

in

color and matrix.

The

variation in these

enormous. Most of the mines are in Nevada, some are in Arizona, and others are in Colorado and New Mexico. Among the better known localities characteristics

is

are:

Fox Mine (Nevada): huge production; active since 1915. Blue Gem Mine (Nevada): large variation in color, noted for blue and green colors in the same stone.

TURQUOISE Stormy Mountain Mine (Nevada): dark blue, hard material

with black chert matrix.

Lander Blue Mine (Nevada):

finely divided spiderweb,

with tiny turquoise specks; this

is

rare

and highly valued

treatments have been performed without detailed knowledge and testing equipment; some of the imitations are very realistic. Spiderweb turquoise is veined with black matrix, in a pattern that looks like crocheted lace. Higher turquoise are generally associated with darker

today.

values

Bisbee (Arizona): intense dark blue material, wispy matrix.

shades and

Kingman

(Arizona):

some deep blue

material has been

in

less

may

treated to improve color.

that

marketplace.

tinge of green.

more

Santa Rita (New Mexico): pale to deep blue colors.

in

Other notable locations in Nevada are the following mines: Papoose, Zuni, Montezuma, Crow Springs, Carlin. Red Mountain, Godber.

than

Massive turquoise

the less porous varieties take a

used

in

is

good

always opaque, and polish.

beads, carvings, and other jewelry.

brownish matrix, which

is

Turquoise

is

One

of these

is

and circulating

in

the

yellow-green in color, a

intense shade than that of variscite, with a density

8% zinc oxide;

A chemical analysis showed more

the mineral

is

named faustite and

is

a

zinc analog of turquoise.

Another turquoiselike material was found

mean

is

cut along with the turquoise

and provides color contrast and pattern. Turquoise

the blue color.

well be labeled turquoise

R.I. of

bluish color.

often has a

tint in

the turquoise range.

that It

green

Several turquoiselike materials have been discovered

Leadville (Colorado): small stones, deep blue with a

Comments:

195

it

to

have a

1.50-1.51, S.G. 2.88, hardness 4-5,

and

A chemical analysis of this material showed

matches the mineral prosopite: CaAl 2 (F,OH)h: in amounts of Cu and yttrium.

addition, there were large

Name:

Turquoise

is

of ancient derivation and

was

originally brought to

frequently simulated by other materials, both natural

Turkish because

and artificial, and pale turquoise is extensively treated to improve the color. It is very difficult to tell that such

Persia (Iran) via Turkey.

it

means

Europe and

u

ULEXITE NaCaB

Formula:

9

5

Crystallography:

•

8H

2

Stone Sizes: Nodules up to several pounds occur. The material is always cut as cabochons; faceting material

0.

Triclinic.

has never been found.

Acicular crystals, nodules

Comments: The fibrous material cuts interesting catseye cabochon gems, but they are curios only since they are much too soft and fragile for wear. The eye can be very strong, however. Sometimes ulexite occurs in seams, consisting of tightly packed parallel fibers. These are transparent along their length, and the packed aggre-

of fibers, tufts (cottonballs), and veins of parallel fibers.

Colors:

Colorless, white.

Luster:

Vitreous to

Hardness:

silky.

1-2.5.

gates act like an array of parallel glass fibers, displaying

Density:

1.65-1.95.

the property of fiber optics.

Cleavage:

a =

Optics: Biaxial

Perfect

(

1.496;

+ ),2V=

Birefringence:

Luminescence:

1

/J

=

1.505;

y =

will transmit

1.519.

Name:

who

some phosphores-

first

is

popular

After the

among mineral

and dry lakes associated

UNAKITE

with other borates.

See: Epidote.

UVAROVITE

See: Garnet.

TV UVITE

stone and cabochon material.

796

enthusiasts.

German chemist George

Nevada. Argentina; Peru; Chile: USSR. California: world's major source; also source of

polished

L. Ulex,

presented a correct chemical analysis of the

species. In playa deposits

is

an image from the bottom of the slab to the been nicknamed

TV stone and

0.023.

cence.

Occurrence:

the material

top. For this reason the material has

78°.

Blue-green in SW,

If

perpendicular to the fiber direction, a piece of ulexite

direction. Brittle.

See: Tourmaline.

V

VALENTIN1TE

See: Senarmontite.

into

cabochons because

VANADINITE

rial

5

)

also tabular, filiform, skeletal.

Red, orange, orange-red, brownish red, pale

Colors:

yellow, yellow, brownish. Rarely colorless; zoned.

Streak:

White

Luster:

Resinous to subadamantine.

Hardness:

is

almost always

in

good

crys-

likely

come from Arizona

or Morocco.

A faceted vanadinite may be considered a

tremendous rarity. Fewer than ten such gems may have been cut. This is unfortunate since the color is rich and beautiful. Arizona crystals tend to be very small, but the ones from Morocco reach a size of several inches.

Hexagonal. Crystals hexagonal prisms,

Crystallography:

would most

Comments:

Pb (V0 4 3 Cl + R As.

Formula:

it

prized by collectors. Potential faceting mate-

tals that are

Name:

In allusion to the composition.

to yellowish.

VARISCITE

A1P0

Formula:

2.5-3.

FeP0 4 2H

Series to Strengite: 4

•

•

2

0.

2H 0. 2

Orthorhombic. Crystals octahedral and

Crystallography: 6.88; range 6.5-7.1.

Density:

very rare; also massive, crusts, nodules.

None. Fracture conchoidal.

Cleavage: Optics:

e

=

2.350, o

=

Brittle.

Uniaxial (— ).

Luster:

Birefringence:

Dispersion:

0.066.

Very

Density: slight,

shades of orange and yellow.

waxy

to dull.

3.5-4.5.

2.2-2.57.

Cleavage:

Crystals:

good

1

direction; fracture conchoi-

dal; brittle.

Not diagnostic.

Spectral:

Crystals vitreous; massive

Hardness:

0.202.

Pleochroism:

Colorless, pale green, dark green, yellowish

Colors:

green, blue-green.

2.416.

Massive: none; fracture splintery to uneven.

Luminescence:

None. Optics:

Occurrence:

Secondary mineral

in

the oxidized zone

of ore deposits, especially lead deposits. Arizona

Mine,

Mammoth

Mine, elsewhere);

(Apache

New Mexico;

a =

Shadow edge

1.563; at

2V

Biaxial (-),

/J

=

1.588;

y =

1.594.

about 1.56. moderate.

Cali-

Birefringence:

fornia; Utah; South Dakota; Colorado.

Chihuahua, Mexico; Algeria; Scotland; Argentina; Tunisia;

Spectral:

USSR;

line at 6500.

Austria; Sardinia.

Mibladen, Morocco: large red to brown crystals.

0.031.

Not diagnostic. Strong

line at 6880,

weaker

Stone Sizes:

Luminescence: Dull green (Lewiston, Utah) or green (Fairfield, Utah) in SW; whitish green in LW from these

small (less

localities.

Faceted gems are extremely rare and always than 1 carat). The material is not normally cut

797

VAYRENENITE

798

Forms by the action of phosphate-bearing

Occurrence:

The only

Comments:

material, reddish-pink in color,

Arkansas; California; Nevada; Arizona; Pennsylvania. Germany; Czechoslovakia; Austria; Queensland, Aus-

Name:

tralia; Brazil;

Spain.

Utah: rich-colored nodules up to 24 inches across, mixed with other massive complex I

airfield County,

phosphates. Tooele, Utah: massive, rich green nodules, suitable for cutting.

Nodules of variscite may weigh many pounds

Stone Sizes:

and have been found up

The

material

is

diameter of about 24 inches.

to a

suitable only for cabochons, but variscite

mixed with other phosphates

is

Comments:

and

are of Pakistani

tiny.

For Heikki Allan Viiyrynen, a Finnish geologist.

VERD ANTIQUE VESUVIANITE

See: Serpentine.

See: Idocrase.

VILLIAUMITE Formula:

NaF. Isometric; crystals tiny; usually mas-

Crystallography: sive, granular.

sometimes cut into spheres

or used in decorative displays.

gems

reported

waters on aluminous rocks.

Colors:

Deep carmine-red, lavender pink

becomes

colorless

Luster:

Vitreous.

to light orange;

heated to 300°C.

if

Variscite has occasionally been used as a

turquoise imitation.

among

very popular

It is

hobbyists

cabochon material because of the interesting patUtah material. Variscite mixed with quartz from Ely, Nevada, has been named Amatrix (for Ameri-

Hardness:

can matrix).

Cleavage:

as a

2-2.5.

terns in the

Name:

name

After Variscia, the old

Germany where

district in

was

it

first

of the Voigtland

found.

2.79.

Perfect

N=

Optics:

4

Not diagnostic.

Luminescence: Occurrence:

Vitreous.

Kola Peninsula, USSR. Los, Guinea: Los is an island

Hardness: Density:

3.183-3.215 (Pakistan Distinct

a=

1

(-),2V=

=

dish crystals, R.I. 3.23).

/J

=

1.658-1.661;

Stone Sizes:

y=

1.664-1.667.

to 1-2 carats.

Quebec

54°.

(Pakistan material R.I.

=

1.639-1.667).

Occurrence:

None

reported.

In lithium pegmatites.

Viitaniemi, Finland.

Pakistan: pink, cuttable material.

Faceted gems are extremely small (approximately 0.5 carat) and exceedingly rare.

Stone Sizes:

Guinea

coast;

1.330-1.332, S.G. 2.79. Ste. Hilaire,

Quebec.

Los material might yield faceted gems up under 2 carats have been cut from

Gems

material.

12.1 (red,

Quebec, cabochon?).

is seldom discussed among colgemstones because until recently no facetable material was known. The material from Los was reported in 1976 and has been cut into tiny gemstones of deep red color. Despite their small size, they are desirable because so few stones exist. The material from Quebec is larger but very scarce. Villiaumite is somewhat water-soluble, and cutters must use special tricks

Comments:

(Pakistan) yellow-pink/light pink/dark

Not reported.

Luminescence:

off the

0.026.

pink.

Spectral:

such as nepheline syenites.

SI: 1.2 (orange-red).

PC: Pleochroism:

=

Francon Quarry, Mt.

direction; brittle.

1.638-1.669;

Birefringence:

In alkalic rocks,

facetable villiaumite occurs in nepheline syenite in red-

5.

Cleavage: Optics:

None.

Pale pink, rose-red.

Colors:

deep

in

druses.

Luster:

strong: yellow/pink to

(OH,F). Spectral:

Biaxial

Anomalous,

carmine-red.

Monoclinic; crystals prismatic or

Crystallography:

direction; brittle.

Sometimes anomalous.

Pleochroism:

BeMnP0

1

1.327; isotropic.

Birefringence:

VAYRENENITE Formula:

Density:

Villiaumite

lectors of rare

(such as using alcohol as a cutting coolant) to facet the material.

Name:

After M. Villiaume, a French explorer

in

whose

VIVIAN ITE Guinea the material was

collection of rocks from

first

discovered.

VIRID1NE

See: Andalusite.

Occurrence: A secondary mineral in ore veins; also occurs as an alteration product of primary phosphate minerals in granite pegmatites; forms as sedimentary concretions.

New Jersey: Delaware; Maryland:

Colorado; California;

VISHNEVITE

199

See: Cancrinite.

Florida.

Canada; Australia; Japan; Germany; USSR; France;

VIVIANITE

England.

Fe3 (P04 )2

Formula:

•

8H

2

Lemhi County, Idaho: fine crystals. Bingham Canyon. Utah: crystals to

0.

Monoclinic. Crystals prismatic, tabuclusters, radial groups. Also massive, bladed,

Crystallography: lar,

equant;

in

Virginia:

Black

South Dakota:

Hills,

5 inches in length.

crystals. in

pegmatites.

Llallagua and Poopo. Bolivia: fine cuttable crystals to

fibrous; crusts, earthy masses.

Colorless (fresh); darkens to shades of green

Colors:

good

Richmond.

and blue, then dark green, dark bluish green, dark pur-

6 inches long.

Ngaoundere, Cameroon: massive

crystals

up

4

to

feet

long, dark in color, cuttable.

plish, bluish black.

Luster:

Stone Sizes:

Colorless, then dark blue after a time.

Streak:

Vitreous, pearly on cleavage; also dull, earthy.

Hardness:

material

is

Faceted gems are rarely cut because the

so soft and fragile.

micaceous, making

it

The

cleavage

is

almost

very difficult to polish gems.

75-100 carats (indices are 1.585/1.603/1.639, S.G. Density:

2.64).

2.64-2.68.

Cleavage:

Perfect

1

direction. Fracture fibrous.

Thin

pieces are flexible and sectile. Optics:

The

Bolivian material, for example, could cut stones up to

1.5-2.

a=

Biaxial (+)

1.569-1.616;

2V=

Birefringence:

/3

=

1.602-1.656;

y=

Comments: Vivianite gems would be difficult

The 1.629-1.675.

63-83°.

The

so fragile and soft that cut

material darkens spontaneously, so the color of an

attractive stone less enticing to

0.040-0.059.

is

to handle safely, let alone wear.

might disappear after a time, making it spend the time cutting such material.

color of vivianite

is

very rich, and a few stones have

been cut anyway. Pleochroism:

Intense: blue/pale yellowish green/pale

yellowish green; or deep blue/pale bluish green/pale

yellow green; or indigo/yellowish green/yellowish

Odontolite teeth) that has

a phosphate (actually fossil bone and been stained by vivianite and may resem-

is

ble turquoise.

olive-green.

Luminescence:

None.

Name:

After J. G. Vivian, an English mineralogist

discovered the species. Spectral:

Not diagnostic.

who

w WARDITE

Comments: NaAl.,(P0 4 )2(OH) 4

Formula:

•

2H

2

0.

Tetragonal. Crystals pyramidal; as

Crystallography:

crusts, aggregates, fibers, spherules.

Name:

Colors:

Colorless, white, pale green to bluish green.

Luster:

Vitreous.

Hardness:

Wardite

After Henry A. Ward, American naturalist and

collector.

WATER SAPPHIRE

Perfect

1

Ah(OH) 3 (P0 4

Formula:

direction. Fracture conchoidal.

Brittle.

+

=

1.586-1.594; e

=

1.595-1.604.

biaxial.

yellow, yellow-brown,

None.

Hardness:

None.

Occurrence:

phosphate masses

In

in

sediments, and

Density:

2.36.

Cleavage:

to uneven. Brittle.

nodules with variscite and other

phosphates. Also at Amatrice

Lucin, Utah. Biaxial

Perfect

a=

Optics: Hill,

Montebras, France: as an alteration of amblygonite. West Andover, New Hampshire: in crystals to 1 cm. Piedras Lavradas, Paraiba, Brazil: greenish white crys1

brownish black. Very

in

pegmatites. in large

to

3.5-4.

Keystone, South Dakota; Pata, California.

Utah:

brown

Vitreous; also resinous to pearly.

Luster:

Luminescence:

(

1

direction. Fracture subconchoidal

1.520-1.535;

/}

=

1.526-1.543;

y=

1.545-1.561.

+ ), 2V=1\°.

Birefringence: Spectral:

0.025.

Not diagnostic.

inch.

Luminescence:

Faceted gems are very rare, cut from Brazilian material. Cabochons are cut of white wardite mixed with green variscite from Utah. Faceted gems

Occurrence:

would

also in

Stone Sizes:

all

tiny; usu-

rarely colorless, bluish.

Not diagnostic.

about

2

White, greenish white, green, yellowish green,

Colors:

0.009.

Pleochroism:

tals to

5H 0.

cal crystal clusters; crusts; stalactitic.

Birefringence:

Fairfield,

•

aggregates of acicular crystals; often spheri-

ally as radial

).

Sometimes anomalously

Spectral:

)2

Orthorhombic. Crystals very

Crystallography:

o (

See: Cordierite

WAVELLITE

2.81-2.87.

Cleavage:

Uniaxial

another of the many phosphates

5.

Density:

Optics:

is

been cut by collectors. It is pale colored and not terribly attractive and is fairly soft and fragile. It is seen far more frequently as cabochons than as faceted stones. that have

be under 2-3 carats in

Occasionally bluish

in

LW

(various

localities).

size.

200

A secondary mineral in hydrothermal veins;

aluminous and phosphatic rocks.

WILKEITE Chester County, Pennsylvania; Alabama; Florida; Colorado; California. Bolivia; England; Ireland; France; Portugal;

Germany:

Czechoslovakia; Bulgaria; Rumania; Tasmania.

Hot Springs. Arkansas:

in fine, spherical

and

groups

of acicular crystals.

Cabochons up

Stone Sizes:

No

faceted

gems

can be cut into extremely interesting stones. These are very difficult to cut because of splintering of

gems

The

individual crystals of

wavellite in the clusters are very small,

would be a tremendous

Name:

who

equant, also

and a faceted gem

in

England,

discovered the mineral.

(calcium oxalate).

Monoclinic. Crystals prismatic or

Colors:

Colorlesss, white, yellowish, brownish.

Luster:

Vitreous to pearly. 2.5-3.

2.19-2.25.

Density:

Good

Cleavage:

in

1

direction, 2 others distinct. Frac-

ture conchoidal. Brittle.

a =

Optics: Biaxial

(

1.489;

/J

=

1.553;

y =

1.649-1.651.

+ ), 2^=80°. 0.159-0.163.

Birefringence:

Dispersion:

0.034.

Not diagnostic.

Spectral:

Luminescence:

WELOGANITE

None.

Coarse crystals occur

Occurrence: Sr.sZr^GjHgOji.

in coal

seams and

concretions (organic origin). Also as a hydrothermal

Hexagonal; crystals hexagonal, barshaped with heavy striations on prism faces, also grooved due to oscillatory growth. Crystals distinctive, terminated by pedion or pyramids. Also massive. Crystallography: rel

White, lemon yellow, amber. Crystals

Colors:

2

rarity.

After William Wavell, a physician

Formula:

H

4

2

in twins.

Hardness:

Comments: Wavellite is a very attractive mineral that is well known to collectors. It is not generally regarded as cabochon material, but its radial aggregate crystal clus-

the radiating crystal clusters.

CaC

Formula:

to several inches in length

can be cut from Arkansas material. have yet been reported.

ters

WHEWELLITE Crystallography:

radial

201

may be

mineral in ore veins. Elk Creek, South Dakota: fine crystals up to 6 length,

among

cm

in

the finest in the world.

Czechoslovakia; France; Hungary; USSR. Havre, Montana:

in

septarian concretions.

Burgk, Germany: crystals up to several inches

in length.

zoned.

Stone Sizes: Vitreous.

Luster:

Hardness: Density:

Crystals are usually very small, colorless.

Faceted gems from these

will

reach a

maximum of about

2 carats.

3.5.

Comments:

Whewellite is one of the most unusual minbecause of its chemical composition and occurrence. It is seldom seen by collectors, and even less thought of as a faceted gemstone. It is really just a curiosity, and there is nothing intriguing about it except its rarity. The dispersion is fairly high but hard to appreciate because of the usual small size of cut gems.

3.20.

erals

Cleavage: Optics:

Perfect; fracture conchoidal.

a =

1.558;

/3

=

1.646;

y =

1.648.

Uniaxial (— ). Birefringence:

Pleochroism: Spectral:

0.090.

None.

Name:

Not diagnostic.

Luminescence:

None

tist

reported.

After William Whewell, English natural scien-

and philosopher.

WILKEITE

Occurrence: In an alkalic sill intruding a limestone St. Michel, Montreal Island, Quebec, Canada.

at

Apatite Group.

Ca (Si04,PO<,S0 4 )j(0,OH,F).

Formula:

5

Crystallography:

Stone Sizes: Clean, yellowish stones (mostly under carat) have been faceted from this material.

NMC: Name:

V2

4.27 (light greyish-yellow); 0.52 (light yellow).

For William E. Logan,

Geological Survey of Canada.

WERNERITE

See: Scapolite.

first

director of the

lar;

Hexagonal. Crystals rounded; granu-

massive.

Colors:

Pale pinkish, yellowish, rose red.

Luster:

Vitreous to resinous.

Hardness: Density:

5.

3.12-3.23.

WILLEMITE

202

Cleavage: Optics:

Imperfect; very o

1

.640- 1 .650; e

brittle.

brown material and

=

troostite.

1

.636- 1 .646.

crystals to 6 inches long, called

Inyo County California: Utah: Arizona: microcrystalsat

Uniaxial (— ).

various localities. Birefringence:

Tsumeb, Namibia: small colorless

0.010.

Not diagnostic.

Spectral:

None

Luminescence:

Mt. Ste. Hilaire, Quebec: blue,

reported.

metamorphosed marbles. USSR: Laacher See, Germany.

Occurrence:

In

Kyshtym, Urals, Crestmore, California:

in

crystals

and bluish

masses.

marble.

gemmy

crystals.

Stone Sizes: Faceted gems are known to a maximum size of about 10 carats, mostly from the Franklin, New Jersey, occurrence. Cabochons to several inches are frequently cut from massive Franklin material. SI: 1.7 and 11.1 (yellow-orange, Franklin, New Jersey). 1

Stone Sizes: Cuttable crystal fragments have been encountered, but I know of no faceted gems.

Comments:

Wilkeite

is

a rare silicate

— sulfate

apatite

been encountered as faceted gems; however, I have seen cuttable crystals that would yield stones in the 1-5 carat range. These would be extremely rare that has not

NMC: PC:

6.75, 0.30 (light blue,

5.39 (pastel orange,

Comments:

New

Cabochons of massive brown

with black franklinite and red zincite

These

latter stones fluoresce vividly in

willemite

in

After R. M. Wilke, mineral collector and dealer

from

in

white calcite.

UV light. Faceted

extremely rare and stones larger than 1-2 museums. Most such stones are pale

is

carats are worthy of

the

Quebec

WILLEMITE

Name: ZnjSiGj.

is

are difficult to polish, and

too soft and fragile for use

After King William

I

in jewelry.

of the Netherlands. Troostite

American mineralogist, Gerard

after an early

Hexagonal

Gems

locality).

the material

Crystallography:

troostite

green, yellow-orange, or brownish green, rarely blue (from

Palo Alto, California.

Formula:

Jersey).

Jersey are attractive, as are cabochons of willemite

stones.

Name:

Quebec).

New

Troost.

(R). Crystals prismatic, short

and stubby or long needles; massive compact; granular. Colorless, white, gray, various shades of green,

Colors:

WILLIAMSITE

See: Serpentine.

yellow, orange, red-brown.

WITHERITE

Vitreous to resinous.

Luster:

Hardness:

3.89-4.10 (usually the latter).

Density:

Orthorhombic. Crystals twinned to pseudohexagonal dipyramids; prismatic; globular,

Crystallography: yield

Cleavage:

BaCOi.

Formula:

5.5.

Series to Strontianite: SrCO,.

Poor. Fracture conchoidal. Brittle.

botryoidal; granular; fibrous.

o=

Optics:

Uniaxial

(

+

1.691; e

=

1.719.

Colors:

).

Birefringence:

0.028.

Luster:

Dichroism variable.

Pleochroism: Spectral:

Weak bands

Luminescence:

New

Intense green or yellow-green Jersey), also in

and

in

SW

LW. Sometimes intensely

its

where Zn

In zinc ore bodies or is

Density:

Cleavage: Optics:

3-3.5.

4.27-4.79.

Distinct

a =

Biaxial (-), 2

phosphorescent (green).

Occurrence:

Vitreous to resinous.

Hardness:

at 5830, 5400, 4900, 4420,

4320; strong band at 4210.

(Franklin,

Colorless, white, gray with a tinge of yellow,

green, or brown.

metamorphic depos-

Birefringence:

present.

Greenland: Belgium: Algeria: Zaire: Zambia. Franklin and Sterling Hill, New Jersey: the foremost willemite occurrence; stubby green crystals and greenish orange masses to several inches in length. Also massive

1.529;

V=

Spectral:

1

direction. Fracture uneven. Brittle.

/3

=

1.676;

y =

1.677.

16°.

0.148.

Not diagnostic. Effervesces

in acid.

Luminescence: Green and yellow in SW (England) with phosphorescence. Yellowish, with phosphorescence, in LW. Fluoresces in X-rays.

WULFENITE Occurrence: A low-temperature mineral in hydrothermal vein deposits. Lockport, New York; Kentucky: Montana; Arizona: California.

Germany; Czechoslovakia; France; Japan; USSR;

Austria;

England.

Minerva Mine. Rosiclare.

yellowish crystals.

Stone Sizes: Witherite is not normally cut into cabochons because the color is too pale to be attractive. Faceted gems, even those under 5 carats, are usually more translucent than transparent.

Comments: faceted, ful,

Witherite

and they are soft and

attribute

somewhat

Name:

very rarely faceted;

fragile as well.

Witherite

rarity.

is

USNM: 1.22. NMC: 4.05. PC: 0.75 (Asbestos, Quebec). Interesting

cabochons have been cut from

wollastonite, especially from the fibrous material (which

and the reddish material from Lake Superior's Isle Royale. Wollastonite is strictly a curiosity and as a mineral is not especially rare. It resembles other white fibrous minerals, however, and is someyields catseye stones)

times difficult to identify without using X-ray techniques. is

if

it

is

quite rare. Stones are not especially beauti-

is

it

can be cut from fibrous and massive material. Very few gems have been reported.

faceted

Comments: Illinois: large

203

is

fairly

Their only major easy to cut but

Facetable wollastonite

exceedingly rare, the material

is

from Asbestos, Quebec (Jeffrey Mine) being singularly notable. Such gems are, moreover, extremely difficult to cut because of the cleavage and fibrosity of the mineral.

difficult to polish.

After William Withering, an English physician

and mineralogist, who

first

Name:

After W. H. Wollaston, British mineralogist and

chemist.

noted the mineral.

WULFENITE

WOLLASTONITE

Formula:

Formula:

Crystallography:

CaSiOi.

lar

Crystallography:

PbMoO^. Tetragonal. Crystals

commonly

tabu-

with square outline; also pyramidal; massive, granular.

Triclinic. Crystals tabular; massive,

Colors:

cleavable, fibrous, granular.

Orange, (various shades), brownish orange,

yel-

low, brownish yellow, yellow-orange, red, brown, yellowish

Colors:

White, colorless, gray, pale green.

Luster:

Vitreous to pearly; silky

Hardness: Density:

Biaxial

gray, tan, greenish

fibrous.

Luster:

Resinous to adamantine.

Hardness:

2.5-3.

2.8-3.09.

Density: Perfect

1

direction. Fracture splintery. Brittle.

a = 1.616-1.640;/}=

(),2K=

Shadow edge

in

Birefringence:

1.628-1.650;

y=

1.631-1.653.

6.5-7.0.

Cleavage:

Distinct

subconchoidal.

38-60°. Optics:

refractometer about 1.63.

o

=

2.405; e

Luminescence:

Dispersion:

Fluoresces blue-green and phosphoresces

SW, same

in

LW, from

is

nonluminescent.

Occurrence:

California (various localities);

Alaska; Pennsylvania;

alkalic

Willsboro,

New

York;

New

Rumania; Finland. Lake Superior: compact, pale red material,

Isle Royale.

for cutting

Stone Sizes:

2.283.

cabochons.

Cabochons up

0.203.

Weak,

Pleochroism:

in

orange to yellow

tints.

Spectral:

Not diagnostic.

Occurrence:

None.

Secondary mineral

in the

oxidized zone

of ore deposits.

Mexico. Ontario and Quebec. Canada; Chiapas. Mexico; Norway;

good

=

0.122.

Luminescence:

Metamorphosed limestones and

igneous rocks.

Italy;

to

California, Alaska,

Pennsylvania. Material from Asbestos, Quebec, Canada,

uneven

0.015.

Birefringence:

in

direction. Fracture

1

Brittle.

Uniaxial (-).

Not diagnostic.

Spectral:

yellow

brown.

4.5-5.

Cleavage: Optics:

if

to several inches in length

Arizona (Glove Mine. Rowley Mine, Red Cloud Mine. Mammoth Mine, others); New Mexico; Nevada; Utah: Wheatley Mines. Chester. Pennsylvania: Loudville. Massachusetts.

Mexico: Los Lomentos. many other locations; Poland: Yugoslavia; Austria: Czechoslovakia; Germany; Sardinia: Algeria; Morocco; Australia.

204

WURTZITE

Tsumeb, Namibia: yellowish tan on edge, some facetable. Stone Sizes:

Most wulfenite

crystals

up

to 5 inches

crystals, especially those

from U.S. localities, are too thin for the cutting of gemstones. However, an occasional crystal is both thick and transparent enough for faceting, notably from the Red Cloud Mine, the Seventynine Mine, and others. Some of these have yielded gems up to about 5 carats. Tsumeb, Namibia, has produced wulfenite crystals several inches across, from which gems up to 50 carats have been faceted. + (orange, SI: 46.1, 15.7, 9.6 (pale yellow, Tsumeb); 10 Los Lomentos, Mexico). PC: 54 (yellow, Tsumeb). DG: 15.25 (yellow, Tsumeb); 9.44 (red, Arizona).

Comments: The red of wulfenite, especially from the Red Cloud Mine in Arizona, is one of the richest colors Specimens of wulfenite are esthetically magand are greatly prized by collectors. The crystal

habit

is

tabular and the individual crystals are usually

very thin, making

fragment.

Gems

it

difficult to find a suitable cutting

are then difficult to cut because of the

its sensitivity to heat and These characteristics make wulfenite totally unsuited for jewelry, but it makes a spectacular collector

softness of the material and vibration.

gem of great rarity. A red wulfenite over ats.

carat

is

extremely

The only

larger stones

come from Tsumeb

material,

but the facetable crystals from this locality were ex-

tremely

uncommon and

very few stones have been cut

from them.

Name: Wulfen,

After the Austrian mineralogist, Franz Xavier

who wrote

a lengthy

monograph

lead ores of Carinthia.

in nature.

nificent

1

scarce, likewise a yellowish or orange one over 1-2 car-

WURTZITE

See: Sphalerite.

in

1785 on the

X

XALOSTOCITE

See: Garnet.

Biaxial

XANTHITE

a =

Optics: (

1.583;

Birefringence:

See: Idocrase.

See: Proustite.

Occurrence:

Monoclinic; crystals acicular; usually

to colorless, pink, light to

reported.

Typically as veinlets in serpentine or in

may be

translucent to

California; Michigan; Virginia; Puerto Rico.

de Xonotla, Mexico.

Tetela

Chalky white

1.593.

transparent.

massive, fibrous or compact. Colors:

None

contact zones. Small fragments

Ca6Si 6 Oi7(OH)2.

Crystallography:

y=

None.

Luminescence:

Formula:

1.583;

None.

Spectral:

XONOTLITE

=

0.010.

Pleochroism:

XANTHOCONITE

/}

+ ).

medium

Lag hi

di Posina, Vicenza.

Italy.

gray.

Stone Sizes: Luster:

Hardness:

Italian material. 6.

polish,

Density:

Cleavage:

Translucent faceted stones (not truly trans-

parent) up to several carats in size have been cut from

Greasy; pearly; dull vitreous.

is

The

material

is

strong, takes a

in

Name:

one direction; tough.

205

good

extremely rare as both a species and as cut

specimens.

2.71.

Good

and

After the Mexican locality.

Y

YUGAWARALITE CaAl

Formula:

2

Spectral:

Si h Oi6

4H

Luminescence:

0.

2

Monoclinic; crystals tabular and very

Crystallography:

Colorless to white.

Luster:

Vitreous.

Hardness:

None

reported.

Occurrence: In veins and crystals in volcanic rocks in Japan and in huge crystals in breccia cavities in India. Yugawara Hot Spring, Kanagawa Prefecture, Japan. Khandivali Quarry, near Bombay, India. Alaska; Iceland; Sardinia: British Columbia.

flat.

Colors:

None.

Stone Sizes:

4.5.

Superb, well-formed, colorless, transparent

up to 3 cm long occur at the Khandivali Quarry, Bombay, India, with physical properties close to the

crystals

Density:

2.23-2.25.

Imperfect; very

Cleavage: Optics:

a =

1.495;

/}

=

literature values for the mineral.

brittle.

1.497;

y =

A few colorless faceted

gemstones have been cut from 1.504.

this

exceptional and

extremely rare material.

Biaxial (+).

Birefringence:

Pleochroism:

Name: 0.009.

None.

206

From

the original Japanese locality.

ZEKTZERITE

ZINCITE

Formula:

Formula:

LiNa(Zr,Ti,Hf)Si60,s.

Orthorhombic; crystals generally pseudohexagonal, transparent to translucent.

Crystallography: ular,

ZnO

very scarce; massive, cleavable, compact, grains.

Dark

Colors:

Pearly on crystal faces, vitreous on cleavage and fracture surfaces. Luster:

Optics: Biaxial

Orange-yellow.

Luster:

Subadamantine

a = (— ).

1.582;

/}

=

1.584;

y =

Cleavage:

0.002.

The material

is

Occurrence:

Uniaxial

virtually isotropic.

number of miarolitic cavities in Okanogan County, Washington.

= 2.013;

e

2.029.

0.016.

None.

In

None.

metamorphosed limestone and

zinc

ores.

Franklin,

New

Jersey: only major locality: massive red

up to 4 inches long, but these were found only in secondary calcite veins. Poland; Spain; Tasmania. ore, also in crystals

sometimes perched on riebeckite

crystals.

Stone Sizes: Colorless faceted gems in the 1-2 carat range have been reported. The material, and hence the cut stones, are exceedingly rare. After Jack Zektzer of Seattle, Washington,

=

0.127.

Occurrence:

small (less than 2 carats) faceted gems. Typical crystals

initiated the investigation of the

direction but difficult. Fracture

).

Luminescence:

known locality. Crystals up to 35 mm in have been found, some transparent enough to yield

Name:

+

Pleochroism:

In a small

in size,

o (

Dispersion:

inert in

the only

mm

1

Birefringence:

None.

a riebeckite granite in

are 4-15

Perfect

conchoidal.

1.584.

Luminescence: Fluoresces light yellow in SW, LW, no phosphorescence either SW or LW.

size

adamantine.

5.68.

Optics:

Pleochroism:

is

to

4-4.5.

Density:

Perfect in 2 directions.

Birefringence:

This

deep yellow, orange-

pure.

6.

2.79.

Cleavage:

if

Streak:

Hardness: Density:

red, brownish red,

yellow; colorless

,

Hardness:

Hexagonal. Crystals hemimorphic and

Crystallography:

tab-

Colorless to pink sometimes with color zoning.

Colors:

+ Mn.

Stone Sizes: Cabochons have been cut from granular zincite in white calcite from Franklin. Faceted gems of Franklin material are very rare, maximum about 20 car-

who

ats.

newly discovered mineral.

Most

range.

207

of the (few) faceted zincites are in the 1-3 carat

208

ZIRCON

SI: 20.1

and 12.3

AMNH:

Philadelphia

New

(red,

New

tion

Jersey).

16.27 (red, Franklin,

New

Academy of Natural

is

Science: 12.7 (red,

and a complete between the low and high type.

called intermediate zircon,

tion exists

Jersey).

Birefringence:

0.008-0.069. Optically uniaxial

(

transi-

+ ).

Jersey).

PC:

3.28 (clean, superbly cut, probably world's finest).

HU:

3.08 (red,

Comments:

New

Zincite

a very rare mineral, essentially

one important locality. Well-terminated crystals were found only up to about 3-4 inches, but larger masses, weighing several pounds, have been encountered in the ore bodies. These are not especially interesting, but cabochons with red zincite, green willemite, and white calcite, peppered with black franklinite, are unique to the Franklin occurrence and are extremely beautiful as well as highly fluorescent. Spheres have also been cut from this material. Cut zincite is one of the rarest of all gemstones. It is seldom completely transparent; usually it is slightly cloudy or translucent. restricted to

Name:

seen even

in

strongest pervasive line

is

at 6535,

is

absent.

6830, 6625, 6605, 6210, 6150, 5895, 5625, 5375, 5160, 4840, 4600, and 4327.

Red zircons may

no spec-

display

at all.

Inclusions: in the

Angular zoning and streaks are sometimes low type. Some silk is seen occasionally, as

and epigenetic cracks stained with Metamict crystals may have bright fissures

well as tension cracks

ZrSi0 4 + Fe, U, Th,

Formula:

Crystallography: dal; often

iron oxides.

Hf.

known

Tetragonal. Crystals prismatic, pyrami-

twinned; rounded pebbles.

Reddish brown, yellow, gray, green, red; ous other colors induced by heating. Colors:

Luster:

The

There are many narrow lines and strong bands across the whole spectrum, ranging from more than 40 lines (Burma green stones) to only a few lines (orange gems from New South Wales, Australia). Heat-treated stones and low types have a weak spectrum. Colorless, blue, and goldenbrown (all heat-treated) stones display one fine line at 6535, and perhaps also a line at 6590. The complex spectrum of other zircons includes lines at 6535, 6910,

seen

ZIRCON

zircon types.

types where a strong spectrum

in identification.

trum

In allusion to the composition.

all

Zircon spectra are very distinctive and useful

Spectral: is

0.039 for

Dispersion:

Jersey).

vari-

Vitreous to adamantine; sometimes greasy.

as angles.

Heating Effects: Heating helps to crystallize partially metamicted zircons and results in a higher specific gravity; the absorption spectrum also sharpens. Heating green Sri Lankan zircon makes it paler in color. Red-

brown

Sri

Lankan material becomes colorless, sometimes Red-brown Thai and Cambodian stones

reddish-violet.

Imperfect. Fracture conchoidal. Very brittle. Zircon crystals usually contain traces of radioactive elements such as U and Th. These decay within the crystals, and over a period of thousands of years result in

Luminescence:

damage to the crystal structure of the host zircon. The damage can be severe enough to destroy the lattice

yellow-orange.

Cleavage:

severe

itself,

ultimately

decomposing the zircon

is

is is

inert,

of zircon

damaged by

radia-

zircons glow dull yellow

in

LW and

may phosphoresce. Zircon may be whitish, yellow, greenor violet-blue in X-rays.

Pleochroism:

Distinct in blue stones:

reddish brown/yellowish brown.

Intermediate Zircon

High Zircon

green; also brown,

brownish green, dark red

brownish orange

1.78-1.85 (almost isotropic)

1.85-1.93

—

1.84-1.970

e

colorless, blue

1.92-1.94 (often 1.925)

1.97-2.01 1 .984)

(often to

0.008

0.008-0.043

0.036-0.059 (usually the latter)

3.9-4.1 (usually about 4.0)

deep sky blue/ Brown:

colorless to yellowish gray. Red: red/clove brown.

Optics

Density

variable.

a typical fluorescent color (SW), also

Some

Low Zircon orange

Birefringence

is

other crystals glow intensely.

essen-

amorphous. This damaged, nearly isotropic zircon undecayed material is

Colors

The fluorescence

material

Mustard yellow

ish, is

called low zircon, whereas the

called high zircon. Material slightly

Some

internally into

a mixture of quartz and zirconium oxide that tially

turn colorless, blue, or golden.

4.1-4.65

4.65-4.8 (usually about 4.70)

ZUNYITE Occurrence: In igneous rocks worldwide, especially granites. Also found as alluvial material. South Dakota; Colorado; Oklahoma; Texas; Maine; Mas-

New

sachusetts;

York;

New Jersey. areas,

Burma: yellowish and greenish stones found in gem gravels with ruby, complex absorption spectrum in these

that

fine-colored zircons are very rare stones, and even smaller

ones are seldom seen in jewelry today. Catseye con has also been reported from Sri Lanka.

colors, in gravels.

all

The crystals

yield these lovely colors are usually reddish-brown. Large,

fine

USSR; Korea; Germany; Brazil. Sri Lanka: one of the most important zircon material of

the colorless and golden yellow shades.

209

Name:

Zircon

from the Arabic zargun, from the

is

Persian zar(gold) plus gun < color).

ZOISITE

zir-

The name

is

ancient.

See: Epidote.

stones.

Thailand: one of the most important commercial sources of

gem

zircon.

Cambodia: chief source (although no current production) of material that heat-treats colorless and blue. France: red crystals at Espaly,

Quebec and

St.

Marcel.

Ontario, Canada: dark,

New South

Formula:

Al„Sis02<>(OH,F), 8 Cl.

opaque

crystals

up

Wales, Australia: fine

gem

material (orange).

Email, Tanzania: white zircon pebbles.

Stone Sizes: The largest zircon gems are from Southeast Asian gem gravels. SI: 118.1 (brown, Sri Lanka); 97.6 (yellow-brown, Sri Lanka); 75.8 (red-brown, Burma); 64.2 (brown, Thailand); 23.5 (green, Sri Lanka); 23.9 (colorless, Sri Lanka); 103.2

octahedrons; twinned.

Colors:

Colorless, grayish, pale beige-brown.

Luster:

Vitreous.

Hardness:

7.

Cleavage:

Easy

Density: Optics:

None.

Pleochroism:

Not diagnostic.

Spectral: (blue); 22.67 (golden);

14.34 (red; 21.32 (white).

Luminescence: Occurrence:

Comments:

vein mineral in

Zircon

When

it is

is

an underrated but magnificent

properly cut,

it

rivals

diamond

in

is not correct and the gem is and lifeless. The dispersion is very high, close to that of diamond. Zircon is very brittle and edges of stones are easily chipped and abraded. Zircon must be worn carefully to prevent damage. The range of color in the material is wide, and many additional colors are produced by heating. High Zircon is fully crystalline and has the highest properties, whereas the low type is metamict, due to

beauty, but often the cutting relatively dull

direction; brittle.

=1.600.

TV

ROM: 23.8 (brown); 17.80 (blue); 61.69 (blue, step-cut). AMHN: 208 (greenish-blue, Sri Lanka). gemstone.

1

2.87.

(blue, Thailand).

Geology Museum, London: 44.27

Isometric, typically in tetrahedral crys-

Crystallography: tals, rarely

to 15 pounds, yield only tiny gems.

Arendal, Norway;

ZUNYITE

Fluoresces intense red (Quartzsite).

At the type

of the internal crystal structure by alpha

tropic,

when

U

and Th. In cases of extreme may appear isowith lower refractive indices and less brilliance

particles released by

damage

to the structure, the material

cut. Interestingly, the dispersion

is

the

same

Ouray County, Colorado, and

both the high and low types. The popular blue color can be produced only by heating zircon; the same is true for

as

an

alter-

Saguache

County. Quartzsite, Arizona: large crystals.

Postmasburg, South Africa:

Kurd

village,

in

aluminous shales.

Gumma Prefecture, Japan: transparent tet-

rahedral crystals. Algeria.

may be found

in Japanese in 1986 However, material but has never been reported. enormous up to 2 cm crystals of zunyite were found in a prospect pit near Quartzsite, Arizona. These are perfect tetrahedra, pale beige-brown in color, in matrix. Minute areas of some of these crystals were perfectly transpar-

Stone Sizes:

ent, colorless,

for

Zuni mine, near

ation product of feldspar in a dike rock in

Cuttable zunyite

(

bombardment

locality, the

Silverton, Colorado, enclosed in guitermanite; also as a

up

to

x

li

Name:

)

and suitable

for cutting into faceted

carat in size.

After the type locality in Colorado.

gems

Gemstones from the Laboratory

HISTORY

1965); quartz (1950);

diamond

(1955; 1970); turquoise

(1972); alexandrite (1973); opal (1974); lapis lazuli (1976);

Humans

have always sought to emulate nature and cap-

ture her secrets.

dreams of

The

early alchemists, building

and jadeite

Many

antiquity, thought they could turn lead into

gold. In like manner, the

dream

at the

tunately, virtually

all

You cannot

of these attempts were

recreate a

complex

doomed

other gemstones have been

of the techniques used to create gemstones in

gemologists.

laboratory

duplication of nature's crystalline masterpieces. Unfor-

failure.

Many

the laboratory were not developed to create misery for

of creating valuable

gemstones has inspired many attempts

(1984).

synthesized but await commercial exploitation.

on the

call

it

an

The almost-magical

art) of crystal

twentieth-century technology,

to

crystals per se. Crystals are

feat of natural

magic unless you understand the magician's trick. And a complete understanding of the structure and formation

science (some would

growth, almost exclusively a is

mainly concerned with

among

the most important

materials of civilization. In fact, nearly

we take for granted today,

all

of the things

able gemstones out of inexpensive chemicals, like turning

forms of transportation, communication, banking, commerce, and manufacture, down to portable radios, TV sets, auto ignitions, and hearing aids, would not work at all without exotic, specially made crystalline materials. It can safely be said that the technology for growing crystals of these materi-

base metal into precious metal — was tempting beyond

als

of natural crystalline solids, even with twentieth-century skills,

remains elusive, although many parts of the puzzle

have been solved. However, the ultimate prize — to actually create valu-

imagination. In fact, as early as 1885, the

first

market-

is

able gemstones were born in laboratory furnaces in France.

Ruby had

actually been

made

all

There advanced

critical to the well-being of society.

is

in technologically

not influenced directly or indirectly

by crystals.

enough for gemFremy and Verneuil opened the door to commercial sapphire and ruby manufacture, and by around 1902 the basic problems had been solved. An earlier gem, marketed in Switzerland and known as Geneva ruby has recently been shown to be a prior, successful

The work

become

no aspect of daily existence

countries that

as early as 1837, but the

material was not transparent or large

stone use.

has

including

Crystal growers

make use

of certain fundamental as-

pects of natural laws; these laws govern the states of

of

matter and the interactions of atoms and molecules. One such law, known as the second law of thermodynamics, states that natural processes tend to run in a direction that produces the greatest entropy. Entropy is the degree of disorder, or randomness, of a system. The tendency of natural processes (that is, the direction in which things

product of the ruby-making procedure developed by

August Verneuil. Once it had been demonstrated that gemstones could be manufactured in commercial size and quality, a new era of intensive research was spawned. At this writing, the following gemstones (and approximate dates of first commercially viable production) have been manufactured: ruby (1885-1905); sapphire (1910); spinel (1910); star ruby and sapphire (1947); rutile (1948); emerald (1950,

tend to go

if

left

entirely to themselves)

is

to

move

in the

direction of lowest energy. In other words, natural processes

spontaneously go energy.

It

in

away

that releases rather than absorbs is released when an atom an already-existing cluster

turns out that energy

or molecule attaches

itself to

of other atoms and molecules la nucleus).

focus of crystal growers

277

is

The major

to use this principle in a

,

GEMSTONES FROM THE LABORATORY

272

controlled way. All crystal growth methods boil

down

to

not favored by thermodynamics. this

change in the system that would cause randomly moving atoms to attach themselves to a nucleus, or seed crystal

Crystal growth

fortuitously provided by the crystal grower.

If

everything

goes according to plan, the atoms attach themselves slowly, deliberately,

and

in a

tural configuration of the

tinues until (1) there are

way

that follows the struc-

seed crystal.

The process con-

no suitable loose atoms

left to

attach, or (2) the energy configuration of the system stabilizes

and the driving force of the process ceases

to operate.

One way

to provide the driving-force energy

is

to

change the temperature of the system. Another way is to change the number of loose atoms available, that is, the saturation of these atoms within the medium in which the crystal is growing. These two general techniqueschanging temperature or changing saturation — are the basic methods by which nearly all laboratory-produced crystals are grown. These are also the two chief methods of crystal growth in natural environments.

plate, or seed crystal, for the

tricky;

is

In light of this,

A

The

random, uncontrolled growth

an effort to alter the energy configuration of a chemical system very carefully; this would create the spontaneous

gemstone

is

it is

many

is

best alternative to to provide a tem-

dumped atoms

to join.

things can go wrong.

absolutely amazing that

gems exist.

a transparent and outwardly perfect crys-

mass, (ideally) free of visible imperfections or

talline

and sometimes of immense size. grow such perfect crystals in a controlled laboratory environment. It is nothing short of miraculous that, given the randomness of natural environments, nature has been able to produce crystals large and perfect enough to yield gemstones. In some cases, humans have yet to figure out how mother nature, the magician, has even been able to pull off the trick! flaws, of uniform color It is

difficult

Following

enough

being

made

an abbreviated summary of the basic

is

methods used

to

to

grow

crystals. All of the

in laboratories are

made by one

gemstones or

more

of

these methods.

Substances best grown from vapor are

Vapor Growth:

those that pass directly from a solid to a vapor

when

heated or those whose components can easily be trans-

CRYSTAL A

crystal

is,

the atoms in a crystal are arranged in regular, periodic arrays or patterns (like wallpaper).

The

object of crystal

add more atoms and perpetuate the pattern. to provide the basic template, and the raw material (loose atoms) remains mobile by being vaporized, melted, or dissolved in a solution. Thus, we

growth

is

to

A seed crystal is used may speak

of vapor growth, melt growth, flux growth, or

solution growth, depending on the

medium used

for

growth is achieved by forcing the growth medium to attach themselves to the seed. This is theoretically relatively simple to do. All that is required is to cause the growth medium to contain more unattached atoms than the medium can handle at a specific temperature. Unfortunately, it is not so easy to make the atoms go exactly where you want them to go. This is why some people speak of the "art and science of crystal growing." Crystallization. Crystal

unattached atoms

human

In

there let's

is

in the

societies,

when

cities

an exodus to the suburbs.

say a solution,

is

become If

too crowded

a growth

medium,

forced to contain an excess of

dissolved material at a given temperature, the energy of

the system

in

solid to

characterized by long-range order; that

is

vapor form. Materials that pass readily from vapor are said to be volatile. In vapor-transport techniques, the desired substance reacts (usually at a high temperature) with another material, and the prodported

GROWTH

may become out of equilibrium at a lower The direction of spontaneous change, the

temperature.

one that results in a lower overall energy for the system, is that which dumps some of the dissolved material back out of solution. If the dumping tendency is strong enough (that is, a very rapid temperature drop) the atoms will actually coalesce into many small nuclei, even though the process of nucleation absorbs energy and is therefore

more volatile than the These newly formed products are

ucts of the reaction are even original substances.

moved

to a

new

location, usually at a lower temperature,

where they react materials.

If

yields single crystals. teristically

way to recreate the starting done carefully, the reaction Vapor-grown crystals are charac-

in a reverse

the procedure

is

long needles or thin plates;

in

some cases

growth yields lacelike aggregates known as dendrites (for example, snowflakes). Vapor-grown crystals include most metals, cadmium crystal

and zinc

gems

sulfides

and arsenides, and various oxides. grown in this way.

No

are commercially

Melt Growth: Most natural crystals were formed in molten environments deep within the Earth. The sizes of the crystals (grains) in a rock and the way in which the grains have grown together are meaningful to geologists and tell a great deal about the cooling history of the rock. Gemstones, including olivine (peridot), feldspars and others, are occasionally cut from larger crystals in such igneous materials. The general term for melt growth is solidification. Everyone grows crystals from a melt. Water, after all, is nothing more than molten ice, a crystalline solid that freezes (solidifies) at only 32°F. Snowflakes, although dendrites, are single crystals of ice. However, the ice cubes in your refrigerator are not. Uncontrolled freezing of a melt generally results in the formation of many tiny crystallites that all grow at the same general rate to fill up

CRYSTAL An

the available space.

ice

cube

is

thus apolycrystalline

aggregate, consisting of a myriad of intergrown crystals.

Poured ingots of molten metals

same way. Growth from the melt is

is

the

very convenient and requires

equipment

in

many cases. This

unsuitable, however, for growing materials

that contain water or volatile als

much

decompose

at their

components; such materi-

melting point. In technical lan-

guage, a "congruently melting" material

is

one

that

does

not change composition at the boundary between the solid

and

liquid state

of high-purity metals.

and can therefore be grown by one

The method

The Bhdgman-Stockbarger Method

(Fig. 7) was deW. Bridgman (American), D. C. Stockbarger (German), and the Russians J. Obreimov, G. Tammann, and L. Shubnikov in the period 1924-1936. A specially shaped container is used, generally a cylindrical tube that tapers to a cone with a small point at one end. The tube is fulled with powder of the desired crystalline material and lowered through a heater (radio-frequency or electrical resistance types are most common), pointed side down. The material in the tube

veloped around the same time by

melts, but the small conical tip

P.

is

the

first

is

some

such as the growth extremely simple in

grow truly immense more than 3 feet across

to

crystals, the largest to date being

and weighing more than a ton (sodium iodide, cesium iodide, and so forth). It is commonly used for the growth of halides, many sulfides, and a variety of oxides. The Vemeuil Technique (Fig. 8), or flame fusion, was developed in the late 1800s by August Verneuil, one of the great pioneers of gemstone synthesis. Verneuil had deposited sealed papers with the Paris

ences

of the following methods.

213

of this technique,

for specialized applications

concept and can be employed

relatively unsophisticated

method

crystallize in

There are many variations adapted

GROWTH

in

1891 and 1892.

documents revealed the

Academy

When opened

in

of Sci-

1910. these

details of Verneuil*s

work on

ruby synthesis, opening the door to large-scale production.

The equipment detailed by

Verneuil was so cleverly

designed that modern factories

still

employ furnaces

with essentially the same specifications as the original.

Perhaps several hundred materials have been grown by the Verneuil method, and it is one of the least costly of all crystal growth techniques. The Verneuil torch is an inverted oxyhydrogen blow-

part of the

container to emerge from the heater. In ideal circumstances (not

all

that difficult to achieve) the first bit of

molten material to

forms a single crystal, rather than a polycrystalline aggregate. Further solidification continues as an extension of the pattern provided by this solidify

Feed hopper

Vibrator

induced seed crystal, until the entire cylinder is frozen, and the container is filled with a single crystal. Flow gauges Tricone burner

Gas controls and regulators

the Bridgman technique, a specially shaped powder of the desired crystal (C), is lowered through a furnace (B). The powder melts and a crystal starts to form in the pointed tip of the crucible as the crucible emerges into a cool part of the furnace. A single crystal grows (D) as the molten material solidifies.

Figure

7. In

crucible, filled with a

The

assembly

surrounded by insulation (A). Reprinted from Joel E. Arem, Man-Made Crystals (Washington, D.C.: Smithsonian Institution Press, 1973), p. 28. entire

is

Figure 8. Diagram of the Verneuil furnace, the tricone burner (left) is used for many synthetic stones. Reprinted from Michael O'Donoghue, A Guide to Man-made Gemstones (New York: Van Nostrand Reinhold. 1983). p. 24.

GEMSTONES FROM THE LABORATORY

274

powder of

torch; a

through

which

rotating rod, rate

is

the substance to be grown

flame, and the molten drops

this

is

slowly withdrawn.

is

dribbled

fall

onto a GAS OUT

The withdrawal

adjusted carefully, so that the molten droplets

and

raining onto the rod solidify in a controlled fashion

build up a single crystal. crystal

is

The

purity of the finished

powder and

a function of the starting

atmosphere

in

which the

crystal

is

grown.

The

BELL JAR

quality of

the Verneuil crystal, or boule (French for ball)

on the purity and particle

GLASS

the

depends

powder, the flame temperature, rate of rotation and withdrawal of the seed rod, and the shielding of the crystal from drafts. Verneuil-type crystals have also been grown using different heat sources, such as plasma arcs and parabolically popularity of the Verneuil

production

is

factories in

illustrated

method

sapphire, ruby, star

corundum,

SILICA

TUBE RF HEATING

mil-

Among

the

way

are

COIL

MELT

spinel, rutile, strontium

and a vast array of oxides and other compounds.

The Czochralski technique was originally developed lization of metals.

method

POWDER FUSED

Europe were turning out hundreds of

in

It is

gemstone

(Fig. 9),

or crystal pulling,

to

measure the speed of crystal-

now

as important as the Verneuil

crystal growth.

the melting of a starting

powder

The technique

involves

in a crucible, generally

A rotating rod lowered into the touches the melt, and then is slowly

platinum, iridium, graphite, or ceramic. with a tiny seed crystal on the end crucible until

it

just

withdrawn. Crystallization

is

at the interface

melt and the seed proceeds in two ways:

between the (1)

Surface

some of the melt slightly out of the crucible onto the seed. Once this material leaves the melt, it cools just enough to solidify, adding to the seed crystal. (2) tension pulls

Also, heat conduction allows the solid to extend very slightly into the melt, assuring that

pulled out to

make

is

the growing crystal ever larger. Crys-

growth continues

tal

ample material

way

cm

pull-rate

is

GAS

A number

enormous— the

of technologically vital

such as pure silicon, are grown by pulling, as are many materials that are cut as gems. These include ruby,

crystals,

attainable in this way, as the

acts as a

Another variation, called edge-defined film-fed growth.

YAG.GGG, alexandrite, and a wide variety of

lines, resulting in

A

problem

in the form and even more complex shapes.

continuous single crystals

of rods, sheets, tubes, arises

when

ers as platinum

and iridium, or

temperature of the crucible

is

The

lowered downward from

the seed, as opposed to the crystal being pulled out of the

zone growth (zone refining) a movable heater moves the melt zone, while the container and

contents remain motionless. Extremely high purities are

the melting point of the

The latter is the case with cubic zirconium

tainer materials.

than they are long.

if

material to be grown exceeds that of the available con-

oxide (CZ) which melts

much wider

materials are so reactive that

they cannot be melted, even in such unreactive contain-

There are several variations on the basic Czochralski method. One, the Kyropoulos technique, was developed by S. Kyropoulos between 1925 and 1935. It is best suited

melt. In

moving melt zone

kind of impurity sweeper.

unusual oxides.

actually

RF LEAD

configurations; the growing crystal follows these out-

mm

size of baseball bats!

to growing crystals

IN -*

been pulled out and added to the rod. normally on the order of 1 to 10

per hour. Czochralski crystals can be

sapphire,

RF LEAD

allows crystals to be pulled through dies with shaped

until the entire

of the crucible have

The

*-

Figure 9. Apparatus for the Czochralski growth of large high-melting crystals such as synthetic ruby, YAG, and GGG; crucible diameter may be as large as 15 cm (6 in). Reprinted from Kurt Nassau, Gems Made by Man (Radnor, Pa.: Chilton, 1980), p. 87.

contents

in this

LID

STABILIZED ZIRCONIA

for crystal

materials produced commercially in this

titanate,

TUBE AND

by the fact that, by the 1920s,

lions of carats of Verneuil crystals annually.

gem

STABILIZED ZIRCONIA

carbon arcs {arc-imaging technique).

reflected

The

size of the feed

at the fantastically

high tempera-

ture of 2750°C. (4982°F)

Single crystal growth of 1970s,

when

CZ was not managed until the

a research group in the

USSR

perfected a

technique (previously known) called skull melting

(Fig.

an open-ended cup made of copper cylinders; the cup is filled with powdered zirconium oxide and heated by radio frequency induction until the powder melts. The region immediately adjacent to the 10).

The

skull

is

,

CRYSTAL High-frequency induction heating

Water-cooled

assembly

skull

coil

Solution Growth:

GROWTH

215

Solutions are perhaps the most

Even the simple making a cup of instant coffee is a study in solubilities, involving different rates and degrees of solubility of such widely different substances as sugar, powdered coffee, and saccharine. If you go swimming at the beach, the slippery uncomfortable feeling you get after awhile is the familiar crystal growth environments. act of

result of

seawater evaporation, leaving a fine crust of

salts on your skin. You can even see the crystal shapes (cubes in the case of sodium chloride) with a magnifying glass. Solution growth has major advantages, including high mobility of dissolved components, convenience, and ease

sodium chloride and other

Melt

of control.

The apparatus

for solution

growth can be as

simple and inexpensive as a pot of water and

mason Porous crust

quart of boiling water, Sintered shell

Growing

(or skull)

crystals

some

most gemstones, however, require far more elaborate and expensive apparatus! Although 5 pounds of sugar can be dissolved in a jars;

it is

unlikely that such high solubilities

can be found among oxides and silicates. In addition, although pure water is an excellent solvent for many compounds, the ones of gemological interest have such low solubilities that, for practical purposes, they may be considered insoluble. As in the case of natural environments, however, a bit of mineralizer (for example, sodium hydroxide) dissolved its

in

hot water dramatically increases

capability for dissolving silicates such as quartz, beryl

and so forth. It is also much more effective to put the water under both high pressure and high temperature.

Under these conditions, called hydrothermal growth. many mineral crystals can be duplicated in the laboratory.

Crystals

Moreover, since these are the same kinds of condi-

tions that prevail in the ground, the resulting crystals

often look strikingly like those found in ore deposits.

A

major difference, however, is size. Nature is relaunconcerned about the corrosion of container walls, the rupturing of growth vessels if the pressure gets too high, or even the exact chemistry (or purity) of the growth solutions. Very high temperatures and pressures are created with impunity. The result can be spectacular indeed: spodumene crystals up to 40 feet long, feldspars the size of railroad boxcars, and people-sized quartz crystals. To date the largest hydrothermal (quartz) crystals grown in laboratories weigh less than a few hundred pounds and are only a foot or so in diameter. The growth of sugar crystals (rock candy) and other salts can be achieved at room temperature and pressure in simple containers. Silicates cannot be grown in this way. These substances can, however, be crystallized in steel cylinders called bombs (Fig. 12), which are loaded with feed material, water, mineralizers, and seed crystals and placed inside a sealed unit called an autoclave (Fig. tively

1 Cooling * water

Cooling f water T

outlet

inlet

y Lowering mechanism Figure 10. Skull melting (cubic zirconia). A- formation of a

porous crust. B: growth of parallel columns. C: solidified melt. Reprinted from Michael O'Donoghue, A Guide to Man-made Gemstones (New York: Van Nostrand Reinhold, 1983),

p.

59.

copper cylinders, however, remains solid because the cylinders are hollow and water cooled. The molten zirconia is thus effectively contained within a 1-millimeter-thick shell of solid zirconia. The entire assembly is allowed to slowly cool, and crystal growth proceeds by nucleation of parallel crystal columns until the entire mass has solidified. A typical skull contains about a kilogram of material, of which half emerges as cuttable CZ. At this writing, zirconium oxide (also hafnium oxide) is the only important gemstone material grown by this method.

1 1 ).

A hydrothermal growth apparatus is a pressure cooker.

The bomb sealed,

is

heated within the device, and, since

expands as the temperature

once the water

the pressure rises

in

it

to is

fill

it

is

the cylinder,

raised.

The

tern-

276

GEMSTONES FROM THE LABORATORY perature the

is

bomb

carefully monitored,

and the water added

to

exactly measured to achieve a predetermined

pressure level.

Hydrothermal synthesis

is

not of great significance for

technological applications, except

in

the case of quartz.

however, of tremendous importance for synthetic

It is,

gemstones because so many natural materials form hydrothermally within the Earth. Among the gems produced in this way are emerald, amethyst, and citrine. Hydrothermal growth is especially suited to materials that contain water or other volatile components and that therefore decompose on melting.

Seeds

Water

Flux Growth:

is

substances familiar to us ful

enough solvent

so forth. Ice

is

to dissolve

can also be melted if water

only a few hundred degrees;

about the solution capabilities It

Nutrient

turns out that a

borax, lithium oxide fluoride, lead oxide ful solvents

it

A

silver-lined laboratory hydrothermal auto-

about 35 cm (14 in) long. Reprinted from Kurt Nassau, Gems Made by Man (Radnor, Pa.: Chilton, 1 980), p. 104. (Courtesy of A. A. Ballman and R. A Laudise, Bell

clave,

Laboratories.)

temperatures of molten ice, what of other molten substances? at

is

and fluoride, and others are powerin fact,

some

crystal growers

should be possible to find a molten-salt

solvent for any given crystal.

Figure 11.

and Other

silicates,

number of compounds, including + molybdenum oxide, potassium

when melted;

believe that

most oxides,

a crystalline solid that melts at 32°F.

crystalline solids

Baffle

an effective solvent for many not, however, a power-

all. It is

The

earliest

gem

crystals,

the rubies of Fremy, were grown from molten-salt solutions of corundum. A vast array of compounds can be grown in this way (Fig. 13), including alexandrite and emerald (Fig. 14), from molten salt (flux) solutions.

INSULATING

BRICK PLUG"~ N

MICA INSULATION

BOMB

HOT PLATE

NICHROME HEATER WINDING

--

INSULATING BRICK

Figure 12. Enclosure and heating arrangement for a laboratory autoclave. Reprinted from Kurt Nassau, Gems Made by Man (Radnor, Pa.: Chilton, 1 980), p. 1 05. Courtesy of A. A. Ballman and R. A. Laudise, Bell Laboratories.)

)

DEFINITIONS PLATINUM CRUCIBLE AND LID

GROWING CRYSTALS

FLUX

TEMPERATURE DETECTOR

mantle

at a

217

depth of 15 or more miles below the surface.

The major obstacle

to diamond synthesis was finding 1 equipment that could produce these conditions, and (2) materials to use in making this equipment that would allow the equipment itself to survive land maintain) these conditions! Success was claimed often in the period 1850-1950, but never truly documented. Unquestionable proof of diamond synthesis was, in fact, not forthcoming until 1955, when scientists at General Electric Co. announced a breakthrough. A 1 ,000-ton press achieved a simultaneous temperature of 5,000°F and pressure of 1 .5 million pounds per square inch. Diamond forms from carbon very quickly (seconds to minutesl at these conditions, and so the production of synthetic diamond for

industrial purposes

(

is

now

routine, with millions of car-

produced annually. However, the production of large, transparent diamond crystals suitable for gemstone use remains technologically elusive, and very expensive. A major breakthrough in this area could well be the most significant development in gemstone synthesis in history. It is not pure fiction to imagine that such a breakthrough could occur within a decade, since gem quality crystals up to about IV4 carats have already been made. ats

HEATING ELEMENTS

-INSULATION

SUPPORT PEDESTAL

DRAINAGE

HOLE

Figure 13. Crucible inside the flux-growth furnace. Reprinted from Kurt Nassau, Gems Made by Man (Radnor, Pa.: Chilton, 1980), p. 80.

DEFINITIONS It is

important to clarify the terminology associated with

laboratory-produced gemstones since some confusion exists in the literature.

The

PLATINUM CRUCIBLE

International

ogy (ICTT)

SCREEN

Committee on Technical Terminolmeetings and

in 1974, after three years of

deliberations, proposed the following definitions:

FEED BERYL

FLUX

Synthetic

(n.)

A

human-produced chemical compound

or material formed by processes that combine separate

elements or constituents so as to create a coherent whole; a product so formed.

Synthetic (adj.) Pertaining

Nl _

Y_

n

to, involving,

or of the nature

of synthesis; produced by synthesis; especially not of

_

natural origin.

Homocreate COOLER

FLOW

HOTTER

Schematic diagram of the flux transport growth emerald used by Gilson. Reprinted from Kurt Nassau, Gems Made by Man (Radnor, Pa.: Chilton, 1 980), Figure

1

4.

of synthetic p.

147.

are within the range of those possessed by the specific variety of the natural substance that the

homocreate

is

intended to duplicate. (adj.) Synthetic and possessing chemical and physical properties that are essentially the same as

Homocreate

Special Methods:

The

previous discussion encompasses

the overwhelming majority of materials. However,

is

growth conditions

(this

a product of extremely high temperatures

and pressures, conditions chiefly found

those of

A

some

was certainly true of cubic zirconia until skull melting became a commercial process!). Perhaps the most notable of these is diamond. crystals require very unusual

Diamond

A human-produced substance (solid, whose chemical and physical properties

(n.)

liquid, or gas)

in the Earth's

is

its

natural counterpart; created the

substance such as emerald,

a homocreate.

to

Its

made

in

same

as.

the laboratory,

properties are specifically designed

mimic those of the equivalent substance produced by GGG, and YAG are

nature. However, cubic zirconia,

true synthetics tory, ral

— simply compounds made

put together from components.

in the labora-

They have no

natu-

counterparts and are used as gemstones based on

GEMSTONES FROM THE LABORATORY

278

their

own

meritorious properties. In other words,

all

homocreate materials are synthetic; but not all synthetics are homocreate. These definitions were unanimously approved by the ICTT and have been adopted by most professional scientific societies. If gemology is ever to consider itself a true science, it will only do so if it begins to walk in step with other disciplines having a cal

much

longer history of empiri-

and theoretical evolution.

CHARACTERISTICS

The marketplace has expressed great concern over the issue of nondetectable synthetics and their impact on gemstone prices. To be sure, a nondetectable homocreate would be a serious problem if no tests could be developed to recognize it. It must be of synthetic stones.

realized that pecuniary interests drive all markets. In the

past few years the emphasis has been heavily weighted

toward making good homocreates since the monetary return for success is immense and far greater than the reward for developing new detection methods. In other words, you can make a lot more money fooling the marketplace with a newly created gemstone than by selling instruments to detect these gemstones.

Each crystal-growing method

is

somewhat unique and

logical field has a lot of catching

We

uses different equipment, chemicals, containers, and so forth. Natural crystals also

grow

in a

wide variety of

and chemical environments. Every crystal-growth its mark on the growing crystal in the form of color zones, inclusions, surface shapes, and so forth. At any given moment during the growth of a crystal the surface is characteristic of both the environmental conditions and the growth process. As material is added to this surface, the newly added layer becomes the new outermost layer. We can therefore say that crystal growth is characterized by a succession of surfaces, and a crystal's history is documented by the record of its surfaces, in a way very analogous to tree rings. Moreover, crystalgrowth environments are seldom absolutely pure. Contaminants may enter the growing crystal and be trapped within it; these may be chemical impurities or somephysical

process leaves

must recognize

up

The gemo-

to do.

that a certain

percentage of homocreate gemstones

(it is

hoped

small)

escape detection and enter the marketplace as natural gemstones. If this percentage is not too great, the market will not be adversely affected.

marketplace

is

It is

when

only

will

a large portion of a

affected by created gemstones that prob-

lems may arise. The pattern seems to be one of increasing awareness, not only among gemologists but also in the public sector. Awareness is the most important aspect of this problem. Most gems can be proven to be either natural or synthetic.

picious

enough

Following

is

to

The

real

danger

is

have the stone tested

a brief

summary

in

not being sus-

in

the

first

place.

of the characteristics

times crystals or bits of foreign substances. Even the

homocreate and synthetic gems produced in laboratories. It must be remembered that overlap in features is common, and single characteristics, with a few notable exceptions, are seldom sufficient for

kinds of surfaces bounding the crystal during growth are

positive identification.

characteristic of the growth process.

Many

of these fea-

under a microscope. Microscopy is therefore unquestionably the most powerful working tool for the gemologist who wishes to distinguish between natural and synthetic materials. This is especially important because most homocreate materials have properties almost identical to their natural counterparts, or properties within the range observed for the natural substances. Easily measured properties such as refractive index, specific gravity, emission spectrum, optic sign, even color, are not always definitive in identifying homocreates. Also, the range of materials and growth methods used today is so vast that considerable experience is required tures are visible, with correct illumination,

to

make

positive identification. Crystal inclusions

may

be so small that magnifications up to 50x or more are required to see them properly; such inclusions may be the only proof of natural versus synthetic origin. Some gemstones, such as amethyst and citrine, are extremely difficult to distinguish, is

impossible.

place

is

The

and

in

some cases

identification

value of a gemstone in the market-

largely a function of rarity, a feature not typical

typical of various

Vapor Growth: gemstones.

This

is

not of major importance for

The most obvious feature might be

dendritic

patterns or zoning.

Melt Growth:

Some

techniques, such as Bridgman-

Stockbarger, would leave virtually no identifying characteristics. Czochralski and Verneuil crystals, however, have such rapid growth rates that certain features become apparent. Melt growth is typified by rounded surfaces versus the plane surfaces found in natural crystals. These are observed as faint (sometimes distinct) lines visible with correct lighting. If you want to see what these so-called curved striae look like, take a telephone book, bend it slightly, and look at the side with a 2x magnifying lens. The image of a stack of gently curved parallel lines is

very similar to the series of parallel bands (actually the

former surfaces of the growing crystal) seen in most Verneuil crystals. Curved striae are instantaneous proof of synthetic origin. They are never found in natural crystals. Pulled crystals do not normally display such series of

features. Instead,

we may find

tiny metallic inclusions that

separated from the container used to grow the material

CHARACTERISTICS (for

example, platinum) and occasional round bubbles.

Round bubbles or tadpole-shaped bubbles with curved tails

are also typical of melt-grown crystals and are posi-

tive identification features.

219

tory in sufficient

been duplicated in the laboranumbers to create identification problems.

Flux Growth:

The most commonly observed

liquid/gas) have not yet

feature

is

flux particles trapped in the synthesized crystal; these

may resemble breadcrumbs or comets, clouds of dustlike Solution Growth: crystals typically

This

grow

is

in

a real gray area since natural

particles, twisted veils,

and so

forth.

hydrothermal solutions. The

highest percentage of misidentified homocreates probably falls into this category. Experience, a good, high-

powered microscope, and a suspicious nature are likely to be a gemologist's most useful tools. Multiphase inclusions (gas/liquid) are found in both natural and solutiongrown crystals, although three-phase inclusions (solid/

No single

feature

may prove

diagnostic

in

some

cases.

Rather, the gemologist must rely on experience and a

broad pattern of features

common

for identification.

Even

some stones to defy analysis. The of thumb is when in doubt, don't buy. If you pay for

for a fine quality natural stone, be sure

it

so,

it is

best rule

the price

can be proven

so.

GEMSTONES FROM THE LABORATORY

220

BERYL- EMERALD

color zones; strong color zoning; Starburst inclusions;

Be?Al Si60m + Cr/V (trace of CI

Formula:

2

dustlike flux, seemingly at surface of in

hydro-

thermal synthetics). Crystallography:

Hexagonal; synthetic crystals (depending on growth method) prismatic, equant, very thin

tabular.

inclusions.

Chatham: Fingerprint

veils;

phenakite crystals; flux

Hydrothermal:

Green (modified by yellow/blue).

Regency (Linde): Portions of seed

crystals;

phenakite

crystals; daggerlike inclusions (nail heads); flattened

Vitreous.

Luster:

but actually

I.G. Farben/Zerfass: Phenakite inclusions; profuse

twisted veils.

Color:

gem

inside the stone.

healed

cracks, with two-phase inclusions visible (high magnifi-

Hardness:

7.5-8.

Cleavage:

Indistinct; fracture

cation); pointed hollow tubes.

conchoidal to uneven;

brittle.

Lech lei'trier Flux

Hydrothermal

Overgrowths

1.560-1 .563

1.566-1.576 1.571-1.576 0.005-0.007

1.578-1.605 1.570-1.599 0.005-0.010

Natural

Optics

1.572-1.600 1.570-1.593 0.005-0.009

e Birefringence Density

2.68-278

1.563-1.566 0.003-0.005 2.65-2.67

2.67-2.71

(usually

over 2.69)

Dispersion:

0.014

Pleochroism:

Distinct: yellow-green/blue-green.

Luminescence:

LW: Gilson = mustard-yellow;

= weak Lennix =

Zerfass

Lechleitner: Parallel color bands; dustlike particles; red;

= bright red; Biron = inert; red; V-beryl = inert; Crystal Research = inert; Seiko = green (distinctive); Chatham = medium to strong redRegency

(Chatham stones transmit UV to 2300 whereas natural stones are opaque below 3000). brown

to red

SW: Gilson =

orange; others inert.

X-rays: Gilson

=

Strong and typical of natural emeralds. V-beryl

(Australia)

may show

rial

growth

Biron: Fingerprints; veils; fractures; nail heads with liquid tails;

and gas; two-phase large inclusions; white comet

gold particles; phenakite; growth features.

Crystal Research: Two-phase inclusions; color band-

Inamori: Two-phase inclusions.

Spectral:

weak band

parallel to

direction; octahedral gold crystals.

ing (in early material).

dull red.

a

wedge-shaped two-phase inclusions

at

6100. Gilson mate-

has a diagnostic line at 4270. Biron spectrum same as

natural.

Inclusions

Flux Grown:

Comments:

Synthetic emeralds typically have slightly lower refractive indices and birefringence than do natural stones. Flux-grown emerald does not show the infrared spectrum characteristic of water in the beryl structure. This infrared spectrum is characteristic only of natural and hydrothermal synthetic emeralds. Flux-grown emer-

low

and show

Gilson: Veil-like feathers.

alds typically have relatively

Lenix: Flux particles; two-phase inclusions resembling

strong red fluorescence in UV. Chlorine appears to be a

diagnostic trace element found only in hydrothermal

feathers.

USSR:

R.I., S.G.,

Flux-void fillings and healed fractures (orangy

brown). Seiko: Flux inclusions, concentrated in a plane between

synthetics.

Other trace elements overlap with natural

material and are therefore not diagnostic. Natural emeralds contain Na,

Mg and Fe in significantly higher amounts

CHRYSOBERYL

221

Tabulated Data on Synthetic Emerald

Source

Birefringence

S.G.

1.566-1.570

0.005-0.010 0.005 0.004 0.005-0.006 0.004-0.005 0.005

2.68-2.71 2.70 2.68 2.67-2.70 2.68-2.71 2.68

1.563

1.568

0005

2.65-2.70

1.558-1.561

1.565-1.575 1.565 1.566

0.003-0.005 0.004 0.004 0.006 0.004 0.003-0.004

2.65-2.70 2.66 2.62-2.65 2.66 2.65 2.64-2.66

e

Hydrothermal Lechleitner

Overgrowth Solid Beryl

sandwich Linde(= Regency) Biron Crystal

Research

1.571-1.601 1.569 1.566 1.566-1.572 1.569 1.571-1.575

1.571-1.610 1.574 1.570 1

.571-1 .578 1.573

(V-beryl)

Inamori (Kyocera) Flux Gilson Seiko Lenix Zerfass

USSR Chatham

1.561

1.562 1.555 1.559 1.560

1.561

1.563 1.565

The Cr content of Lechleitner emerald is approximately 4-10% (weight], with mean R.I. varying .576-1 .605 as the Cr content increases. By contrast, Linde emerald has Cr = 0.3-1 .2% and R.I. (mean] = 1 .568-1 .575. Natural emeralds usually have a maximum Cr content below 2%, but R.I. also varies with other impurities. The properties of Seiko (flux-melt) emeralds are reported as similar to those of other synthetics. Natural emeralds generally have contents of Na and Mg on the order of 1 + weight percent, whereas synthetic emeralds have very low concentrations of these elements Notes:

from

1

(more than 0.1%) than synthetic emeralds but contain lower amounts (less than 18%) of silica and alumina. Regency emerald is the material formerly made by Linde, manufactured under license by Vacuum Ventures, Inc. This material is therefore identical with the Linde product.

CHRYSOBERYL (Alexandrite) BeAl 2

Formula:

4

(+ Cr/Fe).

0.015.

Pleochroism:

Red/orange/green as for natural material.

Transmission in two bands at approximately Spectral: 4900 and 6700; this creates the alexandrite visual color change.

Luminescence: Czochralski crystals fluoresce strong red in UV and X-rays. Seiko material also strong red under LW. Inclusions:

Like natural alexandrite, violet-red/bluish green, lighting source.

Layer of dustlike inclusions parallel to seed

in

Hardness:

may have tiny platinum crystals. Pulled made in the USSR with crystals X 20 x 10 mm reported; these crystals vary

Pulled material

alexandrite has been

up

Vitreous.

Density:

0.009 (flux, Czochralski).

face; strong banding; wispy veils in flux-grown material.

depending on Luster:

Dispersion:

Orthorhombic; synthetic crystals well

Crystallography:

formed. Colors:

Birefringence:

to 100

color with direction: cherry-red/blue-green/yellow-

green. Seiko alexandrite

8.5.

with crystals similar

in

is

made by

3.73 (flux); 3.715 (Czochralski). nal features (tadpolelike bubbles,

Optics: R.I.

=

Biaxial

(

+

).

1.746-1.755 (flux); 1.740-1.749 (Czochralski).

lar to Verneuil. is

distinctive.

A

floating-zone growth,

shape to Verneuil boules:

and so

inter-

forth) are simi-

general overall swirled appearance

GEMSTONES FROM THE LABORATORY

222

Comments:

Large crystals of alexandrite have been pulled from the melt by Kyocera of Japan. Flux-grown material has been marketed by Creative Crystals Co. of

California.

The melt-grown Seiko

same company

material

is

made by

makes synthetic quartz crystals for Seiko watches. The color change is excellent and properties are generally comparable to those of natural the

alexandrite.

A

Optics:

=

o

1.765-1.776; typically

1.762-1.770. Colorless Verneuil sapphire

Uniaxial

=

1.760-1.769.

).

(

Birefringence:

0.008.

that

synthetic chrysoberyl (not alexandrite)

has been grown hydrothermally

in

Czechoslovakia.

Dispersion:

0.018.

As

Pleochroism:

for natural

corundum; dark red rubies

with brownish tone (Kashan) show up. very orangy.

May

Luminescence:

be stronger

in synthetic versus

may phosphoresce after exposure to X-rays, although the Ramaura stones do not. This effect may be correlated with iron content, as synnatural stones. Synthetic rubies

CORAL CaCOi

Formula:

(Aragonite).

Orthorhombic; manufactured and sold

Crystallography:

as cylindrical, massive pieces.

Oxblood

Colors:

red, red, bright rose,

salmon, angel's

thetic rubies typically contain less iron than natural stones.

SW: Rubies fluoresce, all types, weak to strong. Color may be orangy red or yellowish red (Chatham) also dull, chalky red (Ramaura, Lechleitner). Synthetic yellow sapphire

skin.

Dark

Luster:

Translucent.

red.

UV light. Orangy stones coland Cr may fluoresce deep red, and stones

generally inert in

Mn

with Fe and

V

Chatham orange weak orangy or yellowish red, blue

fluoresce orange.

phire fluoresces

sap-

sap-

phire patchy, uneven reaction in shades of chalky greenish/

Hardness:

3.5.

yellowish/brownish red, orange and yellow. dull chalky red to orangy-red,

2.43-2.70.

Density:

is

ored by

Streak:

N=

Weak

=

1.55-1.58).

purplish red where dye

is

con-

centrated.

Comments:

This

is

a Gilson product.

The

grainy tex-

ture is due There are no growth features similar to those seen in natural coral. This material must be considered a coral to the presence of particles of varying size.

stimulant or imitation.

It

moderate, also chalky

weak

chalky whitish blue.

1.468-1.658 (spot average

Luminescence:

Ramaura ruby

bluish-white zones. Lechleitner blue sapphire very

Grainy texture.

Cleavage: Optics:

=

1.757-1.768; e

effervesces (leaving a small

residual red pigment) in HC1.

LW: Fluorescence

usually stronger in rubies than with

SW, dull red, orangy red. Chatham sapphire fluoresces same colors LW as SW, but usually stronger. Ramaura fluoresces chalky dull red to orangy red, moderate to strong. Lechleitner blue sapphire inert in LW. Seiko padparadscha fluoresces strong red. Spectral:

Usually not diagnostic, as synthetic and nat-

ural stones exhibit

much

the

same

spectra. However,

absorption bands at 4500, 4600, and 4700,

and

visible in

many

all

due

to iron

natural yellow, blue and green sap-

phires, are not seen in synthetic stones.

CORUNDUM

Inclusions:

Abd.

Formula:

Hexagonal of growth method.

Crystallography: tion

Pure corundum

Colors:

coloration

is

is

(trigonal);

shape

is

a func-

(Ni+Cr+Fe); yellow-green (Ni+Fe+Ti); green (Co+V+Ni) blue (Fe+Ti); purple/violet (Cr+Ti+Fe); alexandrite color change (V) gold (Cu); pink (Mn); gray (Fe); maroon

Luster:

(Ni).

Vitreous to adamantine.

Hardness: Density:

9.

3.97-4.

1

;

Verneuil: Curved striae (most characteristic), curved zones of small bubbles, swarms of gas bubbles, spherical

gas bubbles, unmelted particles, strings of bubbles.

colorless; impurity-induced

as follows: Pink/red (Cr); yellow-orange

(Co+Cr); yellow

Plato-Sandmeier effect between crossed

polars (interference colors).

Geneva: Same as Verneuil, more bubbles, angular

stri-

ations.

Fremy: Triangular inclusions, so-called coat hangers. Early Hydrothermal: Natural seed with polysynthetic twin lamellae surrounded by synthetic coating; gas bubble trails and liquid feather fingerprints. Chatham: Lacelike fingerprints, netlike mesh inclusions, disseminated Pt platelets. Dense white cloudlike areas; transparent crystals; fractures and healed fractures; Color zoning. Thin white needles. Flux inclusions in varying

typically 4.00.

patterns.

Cleavage: tough.

None. Fracture conchoidal;

slightly brittle;

Kashan: Flux inclusions (conclusive ID); parallel hoses and flux-drop inclusions; fine cloudlike or foglike veils.

CUBIC ZIRCON IA The so-called white

tails

hair-pins or

comets of melt drops with long

are considered diagnostic for Kashan. Very

were grown than

1

diameter of about 10

to a

mm thick

).

tiny inclusions of cryolite also

seem

to be characteristic.

as natural stones

Ramaura: Residual unmelted

flux,

angular or rounded,

shown

white to orange-yellow. Flat or wispy flux fingerprints;

mm

223

(though

less

The so-called Geneva rubies marketed between 1885 and 1903 were recently

be an early Verneuil-type synthetic; stones were generally only a few carats, as the boules were only to

onal black plates).

about U inch across. The flame-fusion boules grown by August Verneuil reached a length of only about inch; however, modern factories, using updated versions of Verneuil's original equipment routinely produce boules 6 inches long and 1 inch in diameter, and ruby boules as long as 17 inches have been grown. Star corundum in a wide range of colors is also routinely grown. The stars in

Czochralski: Very fine striations occasionally seen, nor-

such material are exceedingly sharp and intense, which

mally no growth features or inclusions.

itself aids in distinguishing them from natural star rubies and sapphires. Internal stresses that accumulate during the growth of Verneuil crystals can be relieved only by

comet-tails, growth features, color zoning with wedge-

shaped zones. Knischka: Broad, dustlike clouds; liquid feathers; negative crystals, perched on the ends of long crystalline tubes (characteristic). Unusual two-phase inclusions at high magnification. Flux inclusions, Pt particles (hexag-

Lechleitner: Flux fingerprints and wispy

veils,

ranging

from transparent/colorless to opaque/white; curved striae. Higher concentration of inclusions in sapphire

corundum was

Synthetic

the mass-produced gemstone materials to

The

existence of a ruby

in

crystals are true giants, reaching a size of

an antique setting

corundum

properties of synthetic

are virtually

like

As with

the

of limited usefulness in identification.

vast majority of synthetic products, the critical diagnos-

features are inclusions.

tures

is

almost an

skilled gemologist

The

evaluation of such fea-

and can only be performed by a has examined many natural and

art

who

synthetic stones and

is

much

at as

the

identical to those of natural material. Therefore, optical

tic

has cooled.

come from

measurements, luminescence, spectral data, and the all

it

the earliest of

does not therefore guarantee natural origin, since rubies of sufficient size for cutting were grown a full century ago. Corundum is one of the easiest gems to grow and is amenable to perhaps the widest range of growth methods.

are

allowing the boule to crack after

as a billion carats annually. Czochralski ruby

up to nearly 10 pounds; colorless sapphire crystals grown for military purposes have reached a size of 22 pounds. Flux-grown rubies are typically an inch or two in diameter, and hydrothermal crystals seldom reach a size greater than 3-4 inches.

A

colorless sapphire crystal weighing

in

a crucible.

CUBIC ZIRCONIA = Formula:

Zr0

2

Crystallography:

growth process Colors:

skills,

a

certain small percentage of synthetic stones are misiden-

(+

Y

Phianite (+ Y)

=

Djevalite (+ Ca)

or Ca).

Isometric; crystals irregular due to

(skull melting).

Colorless

if

dopant impurities (see

pure;

many

colors produced by

table).

tified as natural, and in some cases the laboratories cannot make a positive identification either way. This

percentage,

at least at this writing,

is

small enough not to

seriously affect the market for natural gemstones.

corundum is made by dissolving titanium oxide molten corundum and cooling the material at a rate

Cubic Zirconia Dopant Colors

Dopant

Color

Ce Co

yellow-orange-red

Cr

olive

Cu

yellow pink pink yellow pink brown-violet

Star

that allows the dissolved oxide to exsolve as needlelike

accordance with the trigonal symmetry of the host corundum. Reflections from these densely packed crystals produce the crystals of rutile; these orient themselves in

effect

known

Luminescence is a useful diagnostic test; natural blue sapphires do not react to UV light, whereas many Chatham blue sapphires fluoresce a distinct pale greenish color in

LW

and

dull green in

Er

Eu Fe

as a star.

SW. Verneuil sapphires tend

to

fluoresce whitish to milky green in SW.

Ho

Mn

crystals that

The were

early

Fremy rubies were

initially a

few

thin, tabular

mm in size but eventually

lilac

green

Nd

lilac

Ni

yellow-brown

Pr

amber

Tb

brownish green yellow-brown pale green green

Ti

Stone Sizes:

more

than 100 pounds was grown by controlled solidification

thoroughly familiar with their

microscopic appearance. Even assuming such

in

Modern

many as 250+ torches, and global Verneuil production capacity has been estimated

Comments:

The

1

Verneuil factories contain as

versus ruby.

laboratory.

X

Tm V

GEMSTONES FROM THE LABORATORY

224

The cubic form does not crystallize from a melt of pure composition but can be stably promelts at 2750°C.

Vitreous.

Luster:

Hardness: Density:

8-8.5. 5.5-6.0.

=

5.52; blue

Cleavage:

None; fracture conchoidal

what

(good wearability).

brittle

N=

Optics:

=

5.34.

to uneven;

some-

place

weak reddish/greenish yellow

Pink (Er-doped): yellow-green

in

LW,

faint

UV.

green

in

LW,

faint

SW.

in

Orange (Ce-doped): red in LW. Other doped colors inert. Small gas bubbles; tiny solid inclusions,

Inclusions:

often in rows; clouds of tiny particles; striae (rarely).

Stone Sizes: Rough material is limited by the size of the growth apparatus; typical crystal fragments are on the 1

x

made slightly larger if X 3 cm are routinely made.

2 inches but could be

warranted; pieces up to 8

X

3

Comments:

Cubic zirconia (CZ) is the most realistic and popular diamond simulant ever mass produced. It is so diamondlike in appearance that, when first introduced, it fooled many gemologists and jewelers who were not yet aware of its existence in the marketplace. However, it is quickly and easily distinguished from dia-

mond

by thermal conductivity (which

is

much greater in

diamond than in CZ). Special devices such as the Ceres Diamond Probe, distributed by the leading domestic manufacturer of CZ, were created especially for the purpose of separating diamond from its simulants. Zirconia

made

is

the only synthetic

gem

material routinely

with skull-melting techniques. This

method uses a

water-cooled crucible heated by radio-frequency inducCareful temperature control allows the material immediately adjacent (perhaps a 1-mm thick zone) to the crucible wall to remain frozen, while the remainder tion.

of the oxide

is

molten.

but these were very

The

previously used

all

and so

forth)

become

diamond

frozen layer prevents the

molten salt from attacking the crucible, and crystallization is achieved through slow cooling. The process yields irregular masses, not euhedral crystals. Cubic zirconium oxide is, in fact, known as a natural material. It was discovered in 1937 during a routine investigation of some metamict zircons. The monoclinic form of the same composition is known as the mineral baddeleyite. Cubic zirconia is used widely in ceramics because of its high melting point. Pure zirconium oxide

imitations

obsolete.

DIAMOND properties of synthetic

diamond

identical to those of the natural material.

SW. Lilac (Nd-doped): bright peridot green in

1976,

GGG,

The

inUV. Ca-stabilized material: yellow fluorescence in

order of

in

(YAG,

Luminescence:

green

in 1969,

V2 inch).

cubic zirconia gems were introduced into the market-

None.

Y-stabilized material:

grown

first

An enlarged version of the 1969 apparatus later produced much larger crystals, and when

0.058-0.066.

Dispersion:

zirconia were

small (about

2.15-2.18.

Birefringence:

as the cubic modification down to room temperature) by adding stabilizers such as oxides of Ca, Mg, or Y to the melt. Single crystals of cubic

duced (and preserved C-Ox: green

are essentially

Even the

vari-

ous types of naturally occurring diamond (la, lb. Ha, lib) that differ in composition and conductivity have all been synthesized. Attempts to synthesize diamond were made as long ago as 150 years. A full century of experimentation proved fruitless, mainly because the pressure and temperature conditions under which diamond forms could not be attained with apparatus available during this time period. Diamond readily forms from carbon at a temper-

4000°C and a pressure between 1 and 3 milpounds per square inch. These awesome conditions, which prevail in the Earth's lower crust or upper mantle (where diamonds form in nature) can only be duplicated in the lab using specially prepared steels and alloys and ature over lion

cleverly designed equipment, largely pioneered by the

Harvard University scientist-philosopher, Percy Bridgman. In 1954 H. Tracy Hall, a scientist with General Electric,

became the first person to verifiably produce diamonds. The G.E. team included Hall, F. P. Bundy, H. M. Strong, R. H. Wentorf, J. E. Cheny, and H. R Bovenkerk. The initial crystals were quite small, but in 1970 G.E. made crystals

up

to

about

stones from about

k

x

1

to

carat in size, which yielded cut

k

x

carat, in various colors includ-

and blue. Some of these cut stones and crystals were donated in 1971 to the Smithsonian Institution for its permanent collection. The shape of synthetic diamond crystals depends on the temperature of formation, and may be cubes, octahedra, dodecahedra, or combinations of these forms. The addition of B, as in nature, produces a blue color, whereas nitrogen dispersed in the structure gives yellow, brown, and green hues. Free-world production of synthetic diamond is estimated at more than 100 million carats per year. ing yellow

Distinguishing Features:

G.E. synthetics are inert

LW

colorless synthetic

ultraviolet, but

in

SW

in

diamond

fluoresces strong yellow with persistent phosphorescence of the

same

color. Grayish-blue material fluoresces

and

phosphoresces slight greenish yellow; yellow material is inert in SW. Blue and near-colorless material may show a

JADE cruciform pattern of fluorescence. Synthetic diamond

Birefringence:

appears to be characterized by strong short wave UV fluorescence and phosphorescence while remaining inert

Dispersion:

in

YAG = None

Pleochroism:

LW. Near-colorless synthetic

diamond

is

electrically con-

Spectral:

no such natural material has yet been reported. G.E. synthetic diamonds (made with iron-containing flux)

and

also exhibit magnetic reaction, not seen in natural dia-

Luminescense:

mond. Inclusions in these stones include diffuse clouds of tiny pinponts, and rounded, opaque metallic platelike or rodlike flux inclusions. G.E. synthetic diamonds appear strain free in polarized light.

There seem

to be

fundamental differences

magdiamond;

in the

when

the basis of a distinguishing test

measurements are made

sufficient

0.028.

for both

GGG. YAG

and

also has

Cr

For both

YAG and GGG

lines

fluoresces strong yellow in

glow

YAG

GGG.

if

YAG

Cr-doped. ,

colorless mate-

LW, weaker

in

SW. Bright

in X-rays.

Stone Sizes:

Czochralski crystals of

YAG

pulled up to

2x8 inches or about 4 pounds. Czochralski crystals of GGG pulled up to approximately 4x12 inches approximately

netic properties of natural versus synthetic

may form

rial

YAG and GGG. GGG = 0.038-0.045.

for both

Typical R.E. spectrum from dopants for

ductive;

this

None

225

to reveal statistically

or about 35 pounds.

Comments:

True synthetic analogs of natural silicate make in the laboratory, have little technological interest, and have been grown only in very small sizes. However, a huge family of technologically

garnets are difficult to

significant results.

GARNETS (YAG

and

GGG)

compounds with the garnet structure exists, and many of these are commercially manufactured on a large vital

YAG = Y,AKO, GGG = Gd,Ga

Formula:

2

Crystallography:

YAG

for both

.

s

O,

2

.

Isometric; pulled cylindrical crystals

(or

GGG.

and

Colors:

YAG

is

These materials fit the general formula A1B2C3O12 AiB Oi2 if B and C are the same element). Many are compounds of rare earth elements. Variations in both scale.

s

the basic chemistry and dopant impurities can lead to a colorless

if

many

pure;

colors are produced with

vast range of colored crystals with

The

various dopants:

first

gemstone

potential.

of these garnet-structure oxides were

grown

A very important material, YiFe Oi2 (yttrium iron garnet, = YIG) is vital to microwave devices by the flux method.

Dopant

Color colorless

green

Tb

pale yellow yellow-pink pale yellow pale yellow

Tm

yellow-green golden yellow pale green

Dy

Er

Yb Lu

Ho Pr

lilac

Nd

green

Cr

red blue yellow

Mn Co Ti

S.G.

R.I.

4.56 6.06 6.48 6.43 6.62 6.69 6.20 6.30

1.832 1.873 1.854 1.853 1.848 1.842

— —

— —

— — — —

— — —

1.85

1.863

—

s

and computer bubble memories. This compound is jet black. However, two useful laser materials, yttrium aluminum garnet (YAG) and gadolinium gallium garnet (GGG) were recognized as early as 1962 as having gemstone potential. Highly perfect

YAG crystals doped with

Nd were grown from the melt by Czochralski methods in the late 1960s. As a result, colorless and doped YAG became widely available at a low enough cost to stimulate gem use. Oxides of GD and GA are much more expensive than that of yttrium. Moreover,

GGG,

if

even slightly impure,

turns brownish on exposure to ultraviolet light (for example, sunlight).

These

factors, plus a high specific gravity,

GGG. YAG was the dominant diamond imitation of the 1960s and 1970s, essentially completely replacing rutile and strontium titanate in this role. All such simulants were supplanted by have limited the gemstone use of

GGG

is

colorless

if

pure; slightly impure material turns

brownish on exposure to UV. Also red, blue, green, and so forth.

Vitreous for both

Luster:

Density:

GGG TV

cubic zirconia by 1976, so the popularity of both 6-7.

5.06-5.08).

None; fracture conchoidal

to

crystals tend to have twisted, droplike inclusions as well

uneven

for

both

1.90).

For

GGG. For

=

YAG N =

1.92-2.03.

1.83

(Ga-doped

=

YAG

GGG

were short lived. YAGG (Ga-doped YAG) resembles tsavorite and is also grown from flux. These gems have natural-looking feathers and crystals. Pulled

and

as black crystals with square

and

Optics:

GGG. GGG =

7.02-7.09.

Cleavage:

YAG

and

YAG = 8.5; not brittle. YAG = 4.55-4.57 (Ga-doped =

Hardness:

GGG =

YAG

and triangular shapes.

JADE Formula:

NaAlSi 2 06.

Crystallography:

Monoclinic.

GEMSTONES FROM THE LABORATORY

226

Colorless, green (Cr), lavender (Mn|, greenish

Colors:

gray, yellow, black (excess Cr).

Addition of TiO> aids

None.

Birefringence:

Not diagnostic.

Spectral:

whiteness and translucency.

Luminescence: Vitreous.

Luster:

Hardness:

fluoresce pink

6.5-7.

Comments:

at

General Electric produced

jadeite discs, in various colors, within a high-pressure cell.

The

starting material

was a mixture of oxides

first

melted to a glass, then reground and recrystallized within the jadeite P-T stability field. An alternative method was

up and recrystallize (with chemicals added to produce the desired color) natural jadeite. Times involved ranged up to 24 hours, Discs up to V2 inch diameter and Vs inch thickness were produced, but the size could be increased by using larger apparatus. The researchers projected that Imperial quality jade could be produced with this method. The details were published in 1984. A little-known patent dating back to 1951, however, to grind

detailed a process for

making synthetic materials

to

serve as an ideal jadeite simulant. Insufficient information

is

know whether a true homocreate The S.G. of this material was given as

presented to

product was made.

and colors included white, brown, green, yellow, black, and blue. An amorphous material called Siberian jade or reformed jade, manufactured in Japan, is dark green with a hardness of 5-5.5, S.G. = 2.67, and N = 1.523 (anomalously anisotropic), with absorption bands at 4000-4600 and 6000-7000. Inclusions observed in this material include needles of apatite and dendrites. The G.E. jadeite could pose serious detection problems if made in larger sizes. The look of the finished product is strikingly like that of natural jade; microstruc3.2-3.8,

hardness 6-7, soapy-waxy

feel,

tures are slightly different, with the synthetic having a

if

present,

may

LW.

The Gilson product

Comments:

Researchers

Inert; calcite inclusions, in

reacts

much more

read-

to sulfuric acid than natural lapis, with effervescence

ily

and sulfurous fumes evident. It is also decomposed by HC1. The material is quite porous (as much as 5.7% porosity) and the density is consequently much lower than natural lapis. Natural, crushed pyrite is added to the Gilson product to make

more

it

pyrite in natural lapis, however,

shape than the rounded grains not as evenly distributed

in

in

natural looking.

is

more

far

The

irregular in

Gilson material and

is

the rock. Pyrite in Gilson

lapis also tends to pull out of the matrix

during polishing,

a characteristic almost never observed with natural material.

Gilson makes lapis both with and without pyrite.

The Gilson

material consists of synthetic ultramarine

plus two hydrous zinc phosphates.

suggested that

this material

It

has therefore been

be termed an imitation lapis

rather than a homocreate material.

OPAL Formula:

nH

S1O1

2

0.

Noncrystalline (amorphous); aggregate

Crystallography:

of submicroscopic silica particles.

Colors:

Colorless, white, as

made

in

the laboratory,

with variable play of colors produced by diffraction effect.

Body

colors produced also include gray, black, yellow-

brown. Vitreous, pearly.

Luster:

4.5-6+ (natural opal generally

Hardness:

5.5).

glassy-looking second phase present at grain boundaries,

under very high magnification (300-500X). Apparently the composition of the mixture must be pre-

visible

Density:

1.91-2.24 (Gilson); 2.20 (Inamori).

None; fracture conchoidal;

Cleavage:

cisely controlled to prevent the formation of this glassy

phase, a problem that rarity of translucent

may

also account for the

extreme

or transparent natural jadeite.

Nas(AlSi0 4 )6S (= synthetic ultramarine). 2

Crystallography:

Cubic; cryptocrystalline — granular

texture.

Colors:

Dark

Hardness:

1.41-1.45 (Gilson);

N=

1.46

None.

Luminescence:

SW:

strong chalky yellow-green diagnostic for Gilson.

Faint yellow fluorescence in Inamori. Gilson orange

blue, violet-blue

— comparable to the fin-

5.5-6 (natural lapis

=

5.5).

LW:

Faint or

opal

may be

Inclusions: lar

2.46 (average); material

(natural lapis

=

2.81).

Range

is

somewhat porous

=

fire

Occasional gas bubbles. Distinctive cellu-

chicken-wire or snakeskin pattern

Gilson opal; also seen

Comments: AT

no reaction, except Gilson orange

dull blue or green.

in

is

diagnostic of

Inamori.

2.40-3.0.

None; fracture uneven.

Cleavage: Optics:

N=

opal fluoresces bluish white.

est natural lapis.

Density:

Isotropic;

(Inamori).

Birefringence:

LAPIS LAZULI Formula:

Optics:

brittle.

1.50-1.55 (spot).

has also been

about 220

nm

An

opal-like material with

made in

in

good color play

Japan, consisting of plastic spheres

diameter, and bonded with plastic.

The

RUTILE as in

Q+

from layers of uniformly

+ + Q+ +

color play of this material arises natural opal, that

diffraction

is,

packed spheres of constant

in

the

size; in the

same way

case of the plastic

opal, however, the spheres are not silica but polystyrene.

The

R.I.

is

1.485 (corresponding to that of an acrylic

coating on the polystyrene matrix), sometimes with anom-

alous birefringence, and the S.G.

=

LW

and SW give a whitish fluorescence. Tradenames such as Pastoral Opal and neo-noble opal have been used in 1.19.

Both

conjunction with these plastic imitation opals. Gilson material contains distinctly

less

water than

natural opals; white Gilson synthetic also contains meas-

urable amounts of rials.

Gilson opal

Zr0 and 2

is

in

some cases organic mate-

like natural

opal to the unaided eye,

but differences are apparent under magnification.

QUARTZ

where

natural material. In fact, for

it is

perhaps the one synthetic

which no really satisfactory diagnostic test exists to it from natural material. Inclusions that are

separate

clearly natural in origin, or

some kinds

of twinning, are

Large amounts of synthetic citrine and amethyst are the USSR and Japan; the chief Sawyer Research Products Co. of Cleveland, Ohio. However, the most important synthetic amethyst and citrine in the marketplace today is that from Japan. It is hydrothermal and very difficult to distinguish from natural material. Japanese synthetic quartz has liquid-filled feathers and two-phase inclusions, sharp growth zoning parallel to one rhombohedral face, and unique twin structures that are different in appearance from the polysynthetic lamellae seen in natural ameU.S. manufacturer

is

The

a vital electronic material because of

characteristic piezoelectricity, that

is,

in

is

chief distinguishing test for natural vs. syn-

thetic amethyst

is

the appearance of twinning

in

crossed

polarized light.

RUTILE Formula:

the only proof of a natural stone.

Quartz

+ heat = green; Fe + irradiation = violet (amethyst); Co + heat = blue; Al + irradiation = dark brown; irradiation + heat = yellow-green; = colorless quartz. Fe

made commercially

thyst.

Synthetic quartz has virtually identical properties to

227

TiO?.

its

pressure applied

Tetragonal.

Crystallography:

Near colorless

to a slice of quartz crystal produces an electric current, depending on the orientation and thickness of the slice.

Colors:

Conversely, an alternating voltage applied to such a quartz

oxygen are blue-black as grown, but turn slightly yellowish when annealed in oxygen. Light blue colors are the result of oxidation after growth. Yellow-red-amber colors are produced by adding Co or Ni (no oxidation necessary); V and Cr yield red colors, and Be gives bluish white. Mo, W, and U give bluish white and light to dark blue shades.

slice

causes

it

to vibrate.

This effect

is

valuable in com-

munications equipment and oscillators, such as the ones used in crystal watches. Production of synthetic quartz was deemed vital to U.S. security during

World War

II,

but perfection of the

required technology escaped American researchers. Fol-

lowing the war, notes and equipment seized from the

German

laboratory of Dr. Richard

Nacken provided

the

(slightly yellowish);

orange, brown,

red, blue, green, black. Rutile boules slightly deficient in

Luster:

Subadamantine.

Hardness:

6-7.

missing clues, and by 1950 quartz manufacture, centered in

Ohio, was a commercial reality. All synthetic quartz is manufactured using hydrother-

mal transport techniques. The feed material is natural quartz, and the transport medium is an alkali-rich water solution superheated under pressure in an autoclave. Crystals weighing about 15 pounds are routinely produced, but giants as large as 40 pounds have also been made with production equipment. Colored Quartz:

Colorless quartz of high purity, although

Density:

4.25.

Distinct; fracture conchoidal to uneven;

Cleavage:

extremely Optics:

brittle.

o

=

2.61-2.62; e

Birefringence:

=

2.87-2.90.

0.287.

0.28-0.30 (about six times that of diamond ).

Dispersion:

None.

Pleochroism:

Absorption band

technologically valuable, has minimal value as a faceted

Spectral:

gemstone. However, colored quartz gems are a staple of the commercial marketplace and are extremely popular due to widespread availability and low cost. Colorless quartz is amazingly pure. Colors are created by minor amounts of impurities, coupled with the effects of irradiation, typically using cobalt-60. The following treatment processes are widely understood and used commercially: Q + Fe = brown/yellow;

of spectrum.

Luminescence:

at

4250. cuts off violet end

None; blue stones are

slightly electri-

cally conductive.

Comments:

The major period

of manufacture and marwas 1948-1955; this was the first of the long series of diamond imitation gemstones. It is truly a homocreate, but the colors of the manufactured mate-

keting of rutile

GEMSTONES FROM THE LABORATORY

228

are not duplicated in nature.

rial

The

softness,

extreme

brittleness, slightly yellowish cast, and unrealistically

Hardness:

9.5.

3.17-3.20.

Density:

high dispersion prevented rutile from achieving the incredible

market popularity of

later

diamond simulants such

cubic zirconia. Rutile has been grown by

many

as

tech-

None.

Cleavage:

=

o

Optics:

2.65; e

niques, including vapor transport, plasma-arc, Verneuil,

Uniaxial (+).

hydrothermal, flux, and chemical transport. The majority of commercial crystals were made by Verneuil meth-

Birefringence:

ods. Asteriated rutile can be

made by adding approximately

0.5%

Mg oxide and

gen.

Commercial Verneuil production uses

annealing the finished boule in oxy-

0.043.

Approximately 0.09 (about double that of

Dispersion:

diamond).

it from becomoxygen deficient and therefore black. The modified equipment with the added oxygen tube is known as a

Luminescence:

Fluoresces mustard-yellow

plied to the growing boule, preventing

Comments:

ing

abrasive material.

tricone torch.

aluminum

of rutile boules can be improved (that

is,

amount

of

colorless) by adding a small

2.69.

a modified

flame-fusion torch that allows added oxygen to be sup-

The color made nearly

=

oxide.

Silicon carbide It is

made

and well formed, usually very thin, but sometimes thick enough to cut gemstones. The luster, hardness, and disall

excellent for

quantity on the market as a

CaWO,.

Colors:

Wide

synthetic sold on

Tetragonal; crystals usually pulled.

Crystallography:

variety with rare earth dopants, includ-

ing purple; red-brown; pale green; pale yellow; colorless (pure); yellow-brown; dark red; dark yellow-green.

Luster:

diamond simulant or

as a

merits.

scattered small needles.

"SLOCUM STONE" A

silicate glass

with Na,

Mg,

Al,

and

Ti.

Amorphous.

Crystallography: 5.9-6.1.

Colors:

Colorless, white, black, amber, green.

Luster:

Vitreous.

None.

Cleavage: o

=

1.920; e

=

1.937.

Hardness: Birefringence:

5.5-6.5.

0.017.

Density:

Dispersion:

2.41-2.51 (typically 2.48).

0.026.

Cleavage:

A purple stone (Nd-doped) had a distinc-

Pleochroism:

None; fracture conchoidal, tough.

N=

1.49-1.53; kaleidoscopic effect in crossed

spectrum with strong lines at 6670 and 4340 and a distinct band at 5690-5590; other colors also have dis-

Optics:

tinctive absorption spectra.

Birefringence:

tive

Luminescence:

Pale green

=

pink

in

SW; other

colors

fluoresce mostly shades of blue/blue-white in SW.

Comments: or

use, but the material

has never appeared in

4.5-5.

Density:

flux.

own

its

It

Inclusions observed include platy, hexagonal-shaped

Formula:

Optics:

gem

negative crystals, oriented parallel to crystal faces, and

Vitreous.

Hardness:

inexpen-

by fusing sand and coke in an electric furnace. It can also be made in an arc furnace or by flux growth or vapor-phase decomposition. The crystals tend to be platy

tends to have a greenish cast.

SCHEELITE

an important industrial

in large quantities,

sively,

persion are

Formula:

is

LW.

in

Scheelite

is

also

polars.

Luminescence:

None. Inert in

UV

grown from vapor and

Comments: This curious opal imitation made by John Slocum of Michigan can be manufactured in sizes up to

Rh

several centimeters. Magnification reveals thin, irregular

Pulled crystals display gas bubbles, occasionally

Ir inclusions (metallic).

splintery inclusions that create a color play.

These

inclu-

sions are thin pieces of heated and metallicized silica gel.

SILICON CARBIDE

The

Formula:

Bubbles with very unusual shapes are observed in Slocum Stone. The best color play is seen when viewing

SiC.

Crystallography:

Hexagonal; crystals

platy, thin.

colors change with the viewing angle.

the included flakes

on

their large surfaces, rather than

edge-on. This material has achieved an amazingly high Colors:

Green, blue-green,

Luster:

Adamantine.

light green, colorless.

degree of acceptance and popularity for an imitation material.

STRONTIUM TITANATE SPINEL

MgAl 04

Formula:

However, stoichiometric red spinel grown by the Vermay have no excess alumina and therefore

neuil process

(+ impurity dopants).

2

display the

Crystallography:

Isometric; crystals are boules

made

by flame fusion.

Pure mateial is colorless. Impurity dopants brown, green (Cr); blue, green, brown, pink (Fe); yellow, brown, red (Mn); blue (Co); pink (Cu); green (Cr + Mn); blue (Co + Cr); turquoise-blue (Ni). Perhaps as many as 30 distinct colors are produced red,

commercially.

same

physical properties as natural spinel.

color of this material

is

attributable to traces of

cobalt-rich blue spinel to which

Hardness:

7.5-8.

=

Red Verneuil flux

=

=

3.64; Blue Verneuil

3.60-3.66;

=

Red-flux

=

3.63-3.67;

3.59+; Blue-

N = 2.728; Blue Verneuil N = 1.7231.729; Red Verneuil N = 1.720-1.722; Blue-flux N = 1.715; natural N = 1.718 (1.711-1.719). Synthetic spinel, Verneuil

Verneuil-grown and stabilized with aluminum oxide,

compared

typi-

cally

shows

istic

natural reading of 1.718. However, R.I. and S.G.

R.I. of 1.728 as

The

strong cobalt absorption spectrum: S.G.

ness

= 8,JV=

material has a

=

3.52, hard-

1.725.

Asteriated synthetic spinel has also appeared on the

3.63; natural 3.60 (3.59-3.67).

Optics:

added specks of gold

is

to imitate the pyrite in natural lapis.

Verneuil

Density:

Cr

curved striae and tadpole-shaped bubbles have been observed in the material. Chromium apparently produces a green color when introduced into Verneuil boules grown with excess alumina. If the chemistry is made stoichiometric, the boules crack, but some stones have been cut from this material. Some boules (uncharacteristically) show distinct growth striae and bubbles. Ti. Faint

A lapis imitation has been made consisting of a sintered

Vitreous.

Luster:

The and

Colors:

produce

229

to the character-

market.

The

stars are, of course, 4-rayed.

A

weakly cha-

toyant moonstone simulant has also been reported. properties given are:

N=

greenish fluorescence

in

lar star effect; inclusions

The

about 3.64; strong SW, no spectrum, weak, irregu1.728, S.G.

include air bubbles,

agonal. Also strain knots and

some

hex-

anomalous birefringence.

values for flux-grown stones are within the range of natural spinels.

STRONTIUM TITANATE None; fracture conchoidal.

Cleavage:

Formula: Dispersion:

SrTiOj.

0.020.

Crystallography:

None.

Pleochroism:

Typical of dopant. Natural blue spinel char-

Spectral:

acterized by 4600 band due to iron, not seen in (current) synthetics. Stoichiometric red Verneuil spinel has

strong line, not at

all like

Colors:

Colorless

if

pure; dopants produce colors as

follows:

one

the organ-pipe spectrum seen in

natural red spinels.

Luminescence:

manu-

Isometric; crystals generally

factured with Verneuil torch.

Range

display strong green fluorescence in

UV Colorless stones

of colors

(% dopant)

Pale pink (Mn) and yellow-green stones

Dopant

0.001

0.02

3

fluoresce blue-white in UV. Pale blue stones fluoresce

SW, red in LW. Red stones fluoresce UV. Pale blue-green stones fluoresce intense UV.

bright orange-red in

crimson

Cr

yellow in

Growth

Inclusions:

striae

seen

in

corundum

nostic and

may look

like

Bubbles are also not as diagnegative crystals. Also seen are

tiny flat cavities. Flux material

is

free. Crystals in natural stones

remain a

Co

Yellow to yellow-

Fe

Yellow to yellow-

also typically inclusion

dark redred

black

brown

reddish

deep

brown

dark red-

red to blackish red

orange

are not

typical of Verneuil spinel.

Yellow-dark

brown

in

brown

brown

Mn

critical diagnos-

deep red-orange

Yellow/yellow-

orange

to red to

tic feature.

Ni

Stone Sizes: Verneuil boules typically are about 3-5 inches long and 1-1 !6 inches in diameter.

orange

V

Comments:

The key

ing synthetic spinel

is

duced by the alumina

diagnostic feature in distinguish-

Yellow to dark red -brown

orange dark red-

brown

reddish black red to reddish black black

deep

reddish

to

black

the higher R.I. and density pro-

stabilizer in the Verneuil process. Octahedral crystals of red spinel have been grown from

the flux.

Yellow to

CborTa

Light blue to black or

blue-purple

to

black

black

230

GEMSTONES FROM THE LABORATORY

Luster:

Subadamantine.

Hardness:

"BANANAS" Ba NaNbsO,!,. Colorless 2

5-6.

(slightly yellowish).

N-

2.31.

Dispersive.

Density:

5.13.

Cleavage:

BaTid.

yV=

Optics:

BARIUM TITANATE

Indistinct; very brittle.

2.40-2.41.

0.190 (approximately four times that of

diamond).

Luminescence:

ketplace. soft

and

It is

None.

Be Al

This material supplanted rutile in the marnearer to colorless than rutile but is just as

and also

brittle

unrealistically dispersive. Nei-

diamond simulants. Crystals were mass produced by flame fusion, with the usual gas bubble inclusions.

=

dark color = Fe, light blue color = Co). light brown; c — reddish-purple. Strong

absorption lines at 5860, 5670, and 5430.

BISMUTH GERMANIUM OXIDE Isotropic. Bright golden orange. Bii Ge0 or Bi GejOi Hardness = 4.5. TV = 2.07. S.G. = 7.12. 2n

2

4

2

.

BROMELLITE = 8-9. S.G. = 3.0-3.02. R.I. = = 0.015. Fluoresces faint orange

BeO. Colorless. Hardness

SYNTHETIC TURQUOISE

1.720-1.735. Birefringence

Hydrous phosphate of Cu, Al; totally free of which always contains Fe).

Formula:

inLW.

(versus natural turquoise,

CALCIUM TITANATE (PEROVSKITE) CaTiOj. Orthorhombic. Hardness = 5-6. R.I. (mean) = 2.40.

Various shades of blue, intense.

Colors:

Hardness: Density:

6.

jV

=

CaF (doped with

1.59-1.60; opaque.

Birefringence:

colors.

Hardness

rare earths). Isometric.

Colorless: R.I.

None.

=

None.

Pleochroism: Spectral:

No spectrum

turquoise

is

Luminescence:

Comments:

=

evident; the spectrum in natu-

4900;

mainly due to Fe. Inert in

Green: R.I. shows band

SW, gray-blue

in

may

= in

S.G.

1.44;

This material was introduced by Pierre not an imitation, but a true homo-

inert in

in

of

=

3.20;

no absorption spec-

=

3.19-3.21; spectrum

LW.

1.43-1.45; S.G.

deep

bands

red, fine

at 6900, 5300,

and

fluoresce blue.

Red (doped with U): trum, many lines in

LW.

Wide range

=

R.I.

1.44;

S.G.

=

3.18;

RE spec-

yellow-green, sharp line at 3650;

UV.

in 1972. It is

create with the correct crystalline structure and no ap-

CADMIUM SULFIDE (GREENOCKITE)

parent binding agent. Most physical properties match

CdS. Hexagonal. Hardness

those of natural turquoise. is

4.05.

4.

trum; flouresces green

Gilson

=

CALCIUM FLUORIDE (FLUORITE)

None; fracture conchoidal; tough.

2

Optics:

S.G.

2.68-2.75.

Cleavage:

ral

N=

5.90.

colored by Co, grown hydrothermally;

silicate,

Pleochroic: o

ther rutile nor strontium titanate were truly convincing

Fe

=

6-6.5. S.G.

BERYL (also blue beryl,

Comments:

=

Hardness

None.

Birefringence:

Dispersion:

Isotropic.

2.40.

The

best distinguishing test

2.50-2.52. Inert in

SW,

=

faint

3-4. S.G.

orange

in

=

4.7-4.9. R.I.

=

LW.

the microscopic presence (50x or more) of a regular,

fine-grained texture

and

a mottled appearance. Also, the

material dissolves in HC1.

It is

sold by weight

and

it

pro-

sawn blocks by the manufacturer. It is very compact and tough, takes a high polish, and resembles the vided

in

HEMETINE Fe oxides + Pb oxide. Sintered product designed to imitate hematite. S.G.

=

7.

Streak black to reddish black.

Magnetic; natural hematite

is

not.

finest Persian turquoise in color.

LASERBLUE Borosilicate

MISCELLANEOUS SYNTHETIC MATERIALS

Medium

6.5. TV

=

to

1.52.

dark

Heat

LITHIUM TANTALATE

Al Silicate (+ Nd). Amorphous

lavender. Hardness

(glass).

=

sensitive, difficult to cut.

ALEXANDRIUM Li

+ Cu. Amorphous

blue, very intense. Hardness

=

6.5.

N=

(glass).

1.58.

Heat

Light blue to sensitive.

LiTaOv

Trigonal. Colorless. Piezoelectric. Hardness

5.5-6. R.I.: o

=

2.175; e

=

2.18-2.22. Birefringence

= =

ZINC OXIDE

=

0.006. S.G. that of

7.3-7.5. Dispersion

=

0.087 (about twice

VICTORIA STONE (=

A complex

diamond).

Iimori Stone)

silicate glass,

apparently with an amphibole

due

structure; highly chatoyant,

LITHIUM NIOBATE (LINOBATE)

Made

LiNbO.i. Trigonal. Colorless, violet, green, red, blue, yellow. Dichroic.

Hardness

Birefringence

=

=

5+.

0.090. S.G.

=

R.I.:

o

=

2.21

;

e

=

2.30.

4.64-4.66. Dispersion

0.130 (about three times that of diamond). Inert

in

=

231

to

by melting various minerals.

network of fibers. in wide color

Made

range.

=

Nephritelike: R.I. Jadeitelike: R.I.

=

=

1.61; S.G.

=

1.50; S.G.

3.00; hardness

2.80; hardness

=

=

6.

6.

UV.

YTTRIUM ALUMINATE LITHIUM FLUORIDE (+Cr) LiF (+Cr). Hardness = 3-4. S.G. =

2.64.

N=

1.392.

Isotropic.

YAlOi. Isometric. Colorless, doped with rare earths to many colors, including green, red, bluish, orangy

give

pink, pink, blue-violet. TV

=

Isometric. Colorless. S.G.

1.734-1.738. Cleavage

=

=

3.55-3.60.

cubic. Hardness

=

5-6.

N =

May

simulant.

colored (blue/dark blue/green) also by irradiation. Green:

YTTRALOX Y

=

5.35.

be

N=

1.738; S.G.

=

Hardness 8.5. Dispersion 0.033. (just below diamond). Shows rare earth spectrum; a good diamond

MAGNESIUM OXIDE (PERICLASE) MgO.

1.94-1.97. S.G.

=

=

3.75.

Oi or Y,Th) Oi. Isometric. Colorless (turns yellowish = 1.92. S.G. = 4.84. Hardness = 6.5-8. = Dispersion 0.050 (just above diamond). A reasonable if

MAGNESIUM SILICATE (FORSTERITE) Mg Si0.t. Colorless crystals grown by pulling, doped with Ni = green, with V = blue. 2

(

2

2

impure). R.I.

diamond simulant; the Th-doped material is a sintered polycrystalline product, with about 10% Th oxide, and slightly

lower dispersion (0.039).

POWELLITE CaMoOj. Tetragonal. Colorless (pulled crystals). Ho-doped: S.G.

=

4.34; R.I.

=

ZINC ALUMINATE (GAHNITE) ZnAl

1.924-1.984.

4.

2

Isometric; a spinel mineral. TV

Hardness

4.40.

=

=

1

.805. S.G.

=

7.5-8.

PHENAKITE Be

2

SiO*4.

Hexagonal. Colorless; may be turned yellow = 7.5. Blue-green (V-doped):

by irradiation. Hardness S.G.

=

3.0; R.I.

=

ZINC SULFIDE (SPHALERITE, WURTZITE) ZnS. Sphalerite: isometric; N = 2.30; S.G. = 4.06; ness

1.654-1.670.

=

Wurtzite: hexagonal; R.I.: o

TIN OXIDE (CASSITERITE) Sn0 Tetragonal. Colorless to slightly 2.

1.997-2.093. Birefringence

(about ness

=

1V2

=

=

=

0.022; S.G.

=

= 2.378; birefrinhardness = 3.5-4.

=

4.03;

2.356; e

=

=

0.071

ZINC OXIDE (ZINCITE)

6.8-7.1.

Hard-

ZnO.

0.098. Dispersion

times that of diamond). S.G.

6-7.

gence yellowish. R.I.

hard-

3.5-4.

S.G.

R.I.

=

=

2.01-2.03. Hexagonal.

5.43-5.70.

Hardness

4.5.

Homocreate Materials That Have Been Synthesized

ANDRADITE

GROSSULAR

RUTILE

APATITE

HALITE

SANMARTINITE

AZURITE

HEMATITE

SCAPOLITE

BADDELEYITE

IOLITE

SCHEELITE

BERLINITE

JADEITE

SODALITE

BERYL

KYANITE

SPHALERITE

BROMELLITE

LAZURITE

SPINEL

CALCITE

LEUCITE

SPODUMENE

CASSITERITE

MAGNETITE

TAAFFEITE

CERARGYRITE

MALACHITE

TOPAZ

CHRYSOBERYL

MIMETITE

TOURMALINE

CINNABAR

NANTOCKITE

UVAROVITE

CORUNDUM

OLIVINE

VANADINITE

CUPRITE

OPAL

VARISCITE

DIAMOND

PERICLASE

VILLIAUMITE

FLUORITE

PEROVSKITE

VIVIANITE

FORSTERITE

PHENAKITE

WULFENITE

GADOLINITE

POWELLITE

WURTZITE

GAHNITE

PROUSTITE

ZINCITE

GREENOCKITE

QUARTZ

ZIRCON

232

Trade

Names of Synthetics

ALEXANDRITE

Cubic-Z Cubic Zirconia Cubic Zirconia II Cubic Zirconium Cubic Zirconium Oxide

Alexandria-Created Alexandrite (Creative Crystals)

Crescent Vert Alexandrite (Kyocera)

Inamori Created Alexandrite (Kyocera)

COLORLESS SAPPHIRE

CZ

Brillite

Diamonair II Diamondite

Diamondette Diamonflame

Diamond-QU Diamonesque Diamonique III

Emperor-lite

Gemette

Diamonite

Jourado Diamond Ledo Frozen Fire Mr.

Diamon-Z Diconia

Diamond

Thrilliant

Djevalite

Gem Vesta Gem

Fianite

Vega

Phianite

Phyanite

Zircolite

Shelby Singh Kohinoor

CORUNDUM Amaryl

Zirconia

(pale green)

Crown Jewels

Zirconium Zirconium Yttrium Oxide

(colorless)

Danburite (pink) Diamondite (colorless)

EMERALD

Gemini Ruby Gemini Sapphire

Chatham Created Emerald

Syntholite (red-violet)

Gemerald

Ultralite (red-violet)

Gilson Created Emerald

Violite (red-violet)

Emerita (Lechleitner overgrowth Igmerald (I.G. Farbenl Inamori Created Emerald (Kyocera) Linde Created Emerald Lenix Emerald (Lenic Co.) Regency Created Emerald (Vacuum Ventures) Symerald (Lechleitner overgrowth)

Crescent Vert Emerald (Kyocera)

I

Walderite (colorless)

Zirctone (blue-green)

CUBIC ZIRCONIA Cerene

C-Ox

233

TRADE NAMES OF SYNTHETICS

234

GGG

Magalux

Diamonique

II

Galliant

Triple-G

Perigem (yellow-green) Radient Rozircon (pink) Strongite

Wesselton Simulated Diamond (colorless)

RUTILE Astryl

YAG

Brilliante

Capra; Capri

Diamothyst

Gem Jarra Gem Java Gem Johannes Gem Kenya Gem Kima Gem Kimberlite Gem Gava

Amatite Astrilite

Circolite

Dia-Bud Diamite

Diamogem Diamonair Diamondite

Diamone

Lusterlite

Diamonique

Meredith

Diamonite

Miridis

Rainbow Diamond Rainbow Gem Rainbow Magic Diamond

Diamonte Di

Tag

Geminair

Gemonair

Rutania Rutile

Sapphirized Titania Sierra

Alexite

Gem

Kimberly Linde Simulated Diamond

Nier-Gem Regalair

Tania-59

Tirium Gem Titangem

Replique Somerset

Triamond

Titania Titania Brilliante Titania Midnight Stone

Titanium Titanium Rutile Titan Stone

YAG YA1G Yttrium Aluminum Garnet Yttrium Garnet Yttrogarnet

Ultimate

Zaba

Gem STRONTIUM TITANATE Bal de Feu

SPINEL Alumag Aquagem

Brilliante

Continental Jewel (pale blue)

Berylite (pink) Brazilian

Emerald (yellow-green)

Corundolite

Counterfeit

Diamond

Diagem Diamontina

Dynagem

Degussite (blue-lapis imitation)

Fabulite

Dirigem (yellow-green)

Jewelite

Emerada

Kenneth Lane Jewel

(yellow-green)

Erinide (yellow-green)

Lustigem

Jourado Diamond (colorless) Lustergem

Marvelite Pauline Trigere

TRADE NAMES OF SYNTHETICS Rossini Jewel Sorella Starilian

Strontium Mesotitanate Strontium Titanate

Symant Wellington Jewel Zeathite Zenithite

235

MISCELLANEOUS

COMPOUND

NAME EMERALDINE

Stained Chalcedony

LAVERNITE ROYALITE

Glass

SIERRA GEM STAR TANIA TRIPLITINE

Periclase

Rutile coated with sapphire Star rutile

Emerald-coated beryl

triplet

Bibliography

General Anderson, B. W.,

Gem

Testing 9th ed.

Schubnel, Henri-Jean, Pierres Precieuses Dans Le Monde. Paris: Horizons de France, 1972. Shipley, Robert, Dictionary of Gems and Gemologv. Los Angeles,

London: Butterworth,

1980.

Anderson, Frank

J.,

Riches of the Earth.

New

York: Rutledge

Calif.:

Arem,

Joel E.,

Gems and Jewelrv. New

York: Bantam Books,

1975.

Bancroft, Peter,

Gem and Crystal

Treasures. Fallbrook, Calif.:

Western Enterprises— Mineralogical Record, 1984. Bank, Hermann, From The World of Gemstones. Innsbruck, Austria: Penguin, 1973. Bauer, Max, Precious Stones. Charles Griffin & Co., 1904; reprinted in 2 volumes. New York: Dover Publications, 1968.

Cavenago-Bignami, Speranza, Gemmologia. 2nd ed. Milan, Editore Ulrico Hoepli, 1965. and A. Borelli, Simon and Schuster's Guide to Gems and Precious Stones. New York: Simon and Schuster, Italy:

Cipriani, C.

Gem

Arco Publishing,

ABC

Kingdom. New York: Random

1975.

1983.

Internal World of Gemstones. Zurich:

J.,

Jewelry Bainbridge, Henry

Edition, 1974.

Hurlbut, C.

S.,

and G.

S. Switzer,

Gemologv.

New

York: Wiley,

Batsford,

1949,

C,

Peter Carl Faberge. London: B. T. London: Hamlyn Publishing

reprinted,

Group, 1966.

1979.

Kraus, Edward H., and Chester B. Slawson, Gems and Gem Materials. New York: McGraw-Hill, 1939. Kunz, George F. Gems and Precious Stones of North America. Scientific Publishing Co., 1892; reprinted New York: Dover

and 20th Century Jewelry. London: N.A.G. Press, 1980. Black, J. Anderson, The Story of Jewelrv. New York: William Morrow, 1974. Bradford, Ernie, Four Centuries of European Jewellery. CounBecker, Vivienne, Antique

,

Publications, 1968. Jr., Handbook of Gem Identification. Gemological Institute of America, 1972. Gemstones. Alexandria, Va.: Time-Life Books,

Liddicoat, Richard T.,

Los Angeles,

Feltham, Middlesex, England: Spring Books, 1967. Evans, Joan, A History ofJewellery, 1 100-1870. Boston: Boston try Life, 1953, reprinted,

Calif.:

O'Neil, Paul (ed.),

Book & Art, 1970." Flower, Margaret, Victorian Jewellery.

1983.

Parsons, Charles

J.,

San Diego,

Practical

Gem

Knowledge for the Ama-

Lapidary Journal, 1969. Read, Peter G., Dictionary of Gemologv. London: Butterworth teur.

America, 1974.

1958.

House, 1970. Eppler, W. F., Praktische Gemmologie. Stuttgart, Germany: Ruhle-Diebener-Verlag KG, 1973. Greenbaum, Walter W., The Gemstone Identifier. New York: Gubelin, Edward

Institute of

Van Landingham, S. L. (ed.), Geology of World Gem Deposits. New York: Van Nostrand Reinhold, 1985. Vargas, Glenn, and Martha Vargas, Descriptions of Gem Materials. Palm Desert, Calif.: Published by authors, 1972. Webster, Robert, Gems, 3rd ed. Hamden, Conn.: Archon Books,

1986.

Desautels, Paul E., The

Gemological

Sinkankas, John, Gemstones of North America. Princeton, N.J.: D. Van Nostrand, 1959. Sinkankas, John, Gem Cutting. New York: Van Nostrand Reinhold, 1962. Sinkankas, John, Van Nostrand"s Standard Catalog of Gems. Princeton, N.J.: D. Van Nostrand, 1969. Sinkankas, John, Gemstone and Mineral Data Book. New York: Winchester Press, 1972. Sinkankas, John, Gemstones of North America, Vol. 2. New York: Van Nostrand Reinhold, 1976. Smith, G. F. Herbert, Gemstones. 13th ed. New York: Pitman,

Press, 1981.

New York:

A.

S.

Barnes.

1967.

Calif.:

Fregnac, Claude, Jewelery from the Renaissance to Art Nouveau.

London: Octopus Books, 1973. Gere, Charlotte, Victorian Jewelry Design. Chicago: Henry Regnery, 1972. Grigorietti, Guido, Jewelry through the Ages. New York: American Heritage Press, 1969.

Scientific, 1982.

Read, Peter G., Gemmological Instruments. London: NewnesButterworth, 1978. Sauer, Jules R., Brazil: Paradise of Gemstones. Published by author, 1982.

236

.

BIBLIOGRAPHY Heiniger, Ernst A., and Jean Heiniger, Jewels. Boston:

New York Graphics

The Great Book of

Society, 1974.

A History of Jewels and Jewellery. Leipzig, Germany: Edition Leipzig, 1979. Meen, V. B., and A. D. Tushingham, Crown Jewels of Iran. Kuntzsch, Ingrid,

Toronto: University of Toronto Press, 1968. Menzhausen, Joachim, The Green Vaults. Leipzig, Germany: Edition Leipzig, 1970. Sitwell, H. D. W., The Crown Jewels and Other Regalia in the Tower Of London. London: W. S. Crowell, 1953. Snowman, A. Kenneth, Carl Faberge: Goldsmith to the Imperial Court of Russia. New York: Greenwich House, 1983 (reprint, first published 1979).

Diamonds

New York: David McKay,

Argenzio, Victor, Diamonds Eternal. 1974.

Berman, R. (ed.), Physical Properties of Diamond. Oxford: Clarendon Press, 1965. Blakey, George G., The Diamond. London: Paddington Press, 1977.

Bruton, Eric, Diamonds. 2nd ed. Philadelphia: Chilton, 1978. Chapman, Leo, Diamonds in Australia. Sydney: Bay Books, 1980.

Famous. Notable and Copeland, Lawrence L., Diamonds Unique. Los Angeles, Calif.: Gemological Institute of America, .

.

.

1974.

DeBeers Consolidated Mines, Ltd., Notable Diamonds of the World. New York: N. W. Ayer Public Relations, 1971. Dickinson, Joan Y, The Book of Diamonds. New York: Crown, 1965. Field,

J.,

The Properties of Diamond. London: Academic

Press,

1979.

Freedman, Michael, The Diamond Book. Homewood,

Dow

111.:

Jones-Irwin, 1980.

Gaal, Robert A. R, The

Diamond

JD

World.

New

York: Harper

&

Press, 1979. S.,

The Histon and Use of Diamond. London: Methuen.

1962.

Purnell

&

Basil,

Diamond Cutting. Cape Town, South

Africa:

Sons, 1980.

Wilson, A. N., Diamonds from Birth to Eternity. Santa Monica, Calif.:

Specific

Reinhold, 1985. Easby, Elizabeth K., Pre-Columbian Jade

New

Gemological

Institute of

America, 1982.

Gemstones

Beck, Russell

J.,

from Costa

Rica.

York: Andre Emmerich, 1968.

Grabowska, Janina, Polish Amber. Warsaw: Interpress Publishers, 1983.

Gump,

Richard, Jade: Stone of Heaven.

New

York: Doubledav,

1962.

Hansford,

Howard, Jade. New York: American

S.

Elsevier,

1969.

Hartman, Joan M., Chinese Jade of Five Centuries. Rutland. Vt.: Charles E. Tuttle, 1969. Kalokerinos, Archie, In Search of Opal. Sidney, Australia: Ure Smith, 1967. Kunz, George F, and Charles H. Stevenson, The Book of the Pearl. New York: The Century Co., 1908. Laufer, Berthold,/aafe — A Study in Chinese Archaeology and Religion, Publ. 154, Anthroplogical Series, Vol. X. Field Museum of Natural History, Chicago, reprinted. New York:

Dover Publications, 1974. Leechman, Frank, The Opal Book. 5th ed. Sidney, Australia: Ure Smith, 1973. Leiper, Hugh (ed.), The Agates of North America. San Diego, Calif.: The Lapidary Journal, 1966. O'Leary, Barrie, A Field Guide to Australian Opals. Australia: Rigby, 1977 Palmer, J. P., Jade. London: Spring Books. 1967. Pogue, Joseph E., Turquoise, Memoires of the National Academy of Sciences, Vol. XII, part 2, Mem. 2, 3, reprinted. Glorieta, New Mexico: Rio Grande Press, 1974. Rice, Patty C, Amber, the Golden Gem of the Ages. New York: Van Nostrand Reinhold, 1980. Sinkankas John, Emerald and Other Beryls. Radnor, Pa: Chilton,

Mineralogy

Arem, Joel

E.,

New Zealand Jade: The Storv

of Greenstone.

Wellington, Australia: A.H. and A.W. Reed, J970. Chu, Arthur, and Grace Chu, The Collector's Book of Jade. New York: Crown, 1978.

Rocks and Minerals. New York: Bantam Books,

1973.

W., Feldspars. New York: Wiley, 1969. An Introduction to the Methods of Optical Crystallography. New York: Holt, Rinehart & Winston, 1961 Dana, James D., The System of Mineralogy, 6th ed. New York: Barth,

Tom

Bloss,

F.

F.

Donald,

Wiley, 1898.

Deer, W. A., R. A. Howie, and J. Zussman, Rock-Forming Minerals. Vol. (1962), Vol. 2 (1963), Vol. 3 (1962), Vol. 4 (1963), Vol. 5 (1962). New York: Wiley. Evans, R. C, An Introduction to Crystal Chemistry, 2nd ed. Cambridge: Cambridge University Press, 1964. Fleischer, Michael, Glossary of Mineral Species. Bowie. Md.: The Mineralogical Record, 1975. Frondel, Clifford, The System of Mineralogy. Vol.3. The Silica 1

Minerals.

New

Frye, Keith,

Watermeyer,

York:

Dictionary. 2nd ed. Santa

Row, 1981. Lenzen, Godehard, The History of Diamond Production and the Diamond Trade. New York: Praeger, 1966. Maillard, Robert (ed.). Diamonds: Myth. Magic and Reality. New York: Crown, 1980. Orlov, Yu L., The Mineralogy of the Diamond. New York: WileyTnterscience, 1977. Pagel-Theisen, Verena, Diamond Grading ABC. 7th ed. West Germany: published by author, 1980. Sutton, Antony C, The Diamond Connection. Los Angeles: Tolansky,

New

Crown, 1968. Dietrich, R. V, The Tourmaline Group. New York: Van Nostrand

1981.

Diamond

Monica, Calif.: Gemological Institute of America, 1977. Green, Timothy, The World of Diamonds. New York: William Morrow, 1981. Grodzinski, Paul, Diamond Technology, 2nd ed. London: N.A.G. Press, 1942, 1953. Koskoff, David E., The

Dickinson, Joan Younger, The Book of Pearls.

237

York: Wiley, 1962.

The Encyclopedia of Mineralogy. Stroudsburg,

Pa.:

Hutchinson Ross, 1981 (Encyclopedia of Earth Sciences,

vol.

IV

B).

Gleason, Sterling, Ultraviolet Guide to Minerals. Princeton, N.J.: D. Van Nostrand, 1960. Hey, Max, An Index of Mineral Species and Varieties Arranged Chemically. 2nd ed., with Appendix (1963). London: Trustees of the British Museum, 1962. Hurlbut, Cornelius, Dana's Manual of Mineralogy. 18th ed. New York: Wiley, 1972.

Names: What Do They Mean? Van Nostrand Reinhold. 1979.

Mitchell, Richard S., Mineral

New

York:

BIBLIOGRAPHY

238

Palache, C, H. Berman, and C. Frondel, The System of Mineralogy, 2 vols. New York: Wiley. 1944, 1951. Roberts, W. L., G. R. Rapp, and J. Weber, Encyclopedia of Minerals. New York: Van Nostrand Reinhold. 1974.

Gems Made by Man. Radnor, Pa.: Chilton. 1980. O'Donoghue, Michael, A Guide to Man-Made Gem.stones. New York: Van Nostrand Reinhold, 1983. O'Donoghue. Michael. Synthetic Gem Materials. London: WorNassau, Kurt,

shipful

Company

of Goldsmiths, 1979.

Peiser, H. Steffen (ed.), Crystal

Synthetics Arem, Joel E.,

Man-Made Crystals. Washington, D.C.: Smithsonian Institution Press, 1973. Buckley, H. E., Crystal Growth. New York: Wiley, 1951. Elwell, Dennis, Man-Made Gem.stones. Chichester, England: Ellis Horwood; New York: Halsted Press, 1979. Faraday Society, Crystal Growth. London: Butterworth Scientific

Publications, 1959.

Oilman,

New

J. J.

(ed.).

The Art and Science of Growing

Crystals.

York: Wiley, 1963.

Holden, Alan, and Phyllis Singer, Crystals and Crystal Growing. Garden City, New York: Anchor Books (Doubleday). I960. Laudise, Robert A., The Growth of Single Crystals. Englewood Cliffs, N.J.: Prentice-Hall, 1970.

Vol.

1

,

A

Preparation and Properties of Solid Materials. Aspects of Crystal Growth. New York: Marcel Dekker,

Lefever, Robert

Growth. Oxford: Pergamon

Press, 1967.

.

,

1971.

Maclnnes, Daniel, Synthetic Gem and Allied Crystal Manufacture. Park Ridge, N.J.: Noyes Data Corp., 1973.

Westinghouse Research Laboratories, Crystals Perfect and Imperfect. New York: Walker and Co., 1965. Yaverbaum, L. H. {ed.), Synthetic Gem Production Techniques. Park Ridge, N.J.: Noyes Data Corp., 1980.

Journals Journal of Gemmology (London, Gemmological Association of Great Britain; quarterly). Lapidary Journal (San Diego, California: monthly). Gems & Gemology (Los Angeles, Gemological Institute of

America; quarterly). Deutsche Gemologische Gesellschaft

Zeitschrift der

Oberstein,

Germany;

American Mineralogist (Mineralogical Society monthly).

(Idar-

quarterly).

of America;

Gemstone Species and Ornamental Materials (Excluding Varieties)

Actinolite

Brazilianite

Cordierite

Forsterite

Adamite

Breithauptite

Corundum

Friedelite

Albite

Bronzite

Covellite

Algodonite

Brookite

Creedite

Allanite

Brucite

Crocoite

Almandine

Buergerite

Cryolite

Amber

Bustamite

Cuprite

Amblygonite

Bytownite Calcite

Datolite

Anatase

Canasite

Diamond

Andalusite

Cancrinite

Diaspore

Andesine Andradite

Cassiterite

Dickinsonite

Catapleiite

Anglesite

Celestite

Anhydrite

Ceruleite

Diopside Dioptase Dolomite

Ankerite

Cerussite

Dravite

Anorthite

Dumortierite

Antigorite

Chabazite Chambersite Charoite

Apatite (G)

Childrenite

Elbaite

Danburite

Ekanite

Apophyllite

Chiolite

Enstatite

Aragonite

Chlorapatite

Eosphorite

Chondrodite Chromdravite Chromite Chrysoberyl

Epidote

Barite

Chrysocolla

Euxenite

Bayldonite

Chrysotile

Benitoite

Cinnabar

Augelite Axinite (G)

Azurite

Gahnite Gahnospinel Galaxite

Garnet (G)

Amphibole (G)* Analcime

Anorthoclase

Gadolinite

Ettringite

Gaylussite

Grandidierite

Grossular

Gypsum Hambergite Hancockite Haiiyne Hedenbergite Hematite

Hemimorphite Hercynite Herderite

Hodgkinsonite Holtite

Hornblende

Euclase

Howlite

Eudialyte

Huebnerite

Humite Hureaulite

Feldspar (G)

Hurlbutite

Hydrogrossular

Beryl

Clinochrysotile

Fergusonite

Beryllonite

Clinohumite

Ferridravite

Bismutotantalite

Clinozoisite

Ferroaxinite

Boleite

Cobaltite

Ferrosalite

Boracite

Colemanite

Fluorapatite

Idocrase

Bornite

Coral

Fluorite

Inderite

*(G) indicates names referring to groups (not distinct species).

239

Hydroxylapatite

Hypersthene

240

GEMSTONE SPECIES AND ORNAMENTAL MATERIALS (EXCLUDING

Jade (G) Jadeite Jeffersonite

Jeremejevite Jet

Natromontebrasite Nepheline Nephrite Neptunite

Kurnakovite Kyanite

Labradorite

Langbeinite

Taaffeite

Talc

(= soapstone

=

steatite)

Tantalite Salite

Tektite

Samarskite

Tephroite

Sanidine Sapphirine

Thaumasite Thomsonite

Olivine (peridot) (G)

Sarcolite

Tinzenite

Opal

Scapolite (G)

Orthoclase

Scheelite

Topaz Tourmaline (G)

Schefferite

Tremolite

Schorl

Triphylite

Schorlomite

Tsilaisite

Scolecite

Tugtupite

Scorodite

Turquoise

Obsidian Oligoclase

Orthoferrosilite

Lawsonite Lazulite

Painite

Lazurite (lapis lazuli)

Palygorskite

Legrandite

Rutile

Niccolite

Norbergite

Kammererite Kornerupine

Rhodochrosite Rhodonite

VARIETIES)

(=

attapulgite)

Scorzalite

Lepidolite

Papagoite

Sellaite

Leucite

Pargasite

Ulexite

Senarmontite

Liddicoatite

Uvarovite

Parisite

Serandite

Linarite

Pearl

Uvite

Serpentine (G)

Lizardite

Pectolite

Shattuckite

Ludlamite

Pentlandite Periclase

Magnesioaxinite

Petalite

Magnesiochromite Magnesite Malachite Manganaxinite

Phenakite Phosgenite Phosphophyllite

Piedmontite

Manganotantalite

Pollucite

Marcasite

Powellite

Marialite

Prehnite

Meionite Meliphanite (= melinophane)

Prosopite

Mellite

Proustite

Pumpellyite

(=

chlorastrolite)

Mesolite

Purpurite

Microcline

Pyrargyrite

Microlite

Pyrite

Milarite

Pyrope

Millerite

Pyrophyllite

Mimetite Monazite Montebrasite Mordenite

Pyroxmangite

Shortite Siderite

Sillimanite

(=

fibrolite)

Simpsonite

Vanadinite Variscite

Vayrenenite Vesuvianite Villiaumite Vivianite

Sinhalite

Smaltite

(= skutterudite) Smithsonite Sodalite

Sogdianite Spessartine Sphalerite

Sphene (= titanite)

Wardite Wavellite

Weloganite Whewhellite Wilkeite

Willemite Witherite Wollastonite

Wulfenite Spinel Spinel (G)

Spodumene

Xonotlite

Staurolite Stibiotantalite

Yugawaralite

Pyrrhotite Stichtite

Quartz

Stolzite

Zektzerite

Strontianite

Zincite

Sturmanite

Zircon

Nambulite

Realgar

Sugilite

Zoisite

Natrolite

Rhodizite

Sulfur

Zunyite

Mineral

Groups

of

Gemological Interest

(NOTE: only

HUMITE GROUP

species of gemological interest have been

Chondrodite

listed)

Clinohumite

Humite

Norbergite

AMBLYGONITE GROUP Amblygonite

OLIVINE

Natromontebrasite

Montebrasite

AMPHIBOLE GROUP Hornblende

Actinolite

GROUP

OSUMILITE GROUP

Tremolite

Osumilite

Milarite

Ferroactinolite

Acmite

Carbonate-fluorapatite

Pyromorphite

Mimetite

Hypersthene

Witherite

Strontianite

SODALITE GROUP

BARITE GROUP

Hauyne

Lazurite

Nosean

Sodalite

Celestite

SPINEL

CALCITE GROUP Magnesite

Enstatite

Spodumene

Jadeite

Rutile

Cassiterite

Cerussite

Calcite

Clinoenstatite

Diopside

RUTILE GROUP

ARAGONITE GROUP

Anglesite

Augite

Clinohypersthene

Vanadinite

Barite

Sugilite

PYROXENE GROUP

Carbonate-hydroxylapatite

Aragonite

Sogdianite

Pargasite

APATITE GROUP Fluorapatite

Tephroite

Forsterite

Fayalite

GROUP Gahnite Galaxite Magnesiochromite Magnetite

Chromite

Rhodochrosite

Siderite

Franklinite

Hercynite

Smithsonite Spinel

EPIDOTE GROUP Allanite

Clinozoisite

Piedmontite

Epidote

TOURMALINE GROUP

Hancockite

Buergerite

Zoisite

Schorl

FELDSPAR GROUP Albite

Chromdravite

Labradorite Andesine Anorthite Anorthoclase Celsian

Oligoclase

Bytownite

Hyalophane

Microcline

Dravite

Uvite

Liddicoatite

Elbaite

Ferridravite

Tsilaisite

ZEOLITE GROUP

Orthoclase

GARNET GROUP

Analcime

Chabazite

Mesolite

Natrolite

Stilbite

Almandine

Andradite Grossular Hydrogrossular Kimzeyite Goldmanite Pyrope Schorlomite Uvarovite Spessartine Knorringite Yamatoite

247

Thomsonite

Heulandite

Gmelinite Pollucite

Scolecite

Yugawaralite

45

40

«

35

3 13 •c

u

30

25

23

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

Graph of index of refraction plotted against critical angle, as determined by the formula: Critical angle = arcsin (1/n) where n is the refractive index. This graph is most useful to the gem cutter for determining main pavilion angles. Maximum brilliance is achieved when the pavilion main angle is slightly greater than the critical angle. This can be determined for any given gem material with a quick refractive index measurement on a polished surface prior to cutting the pavilion.

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Index

Achroite, 190

Anglesite,42

Benitoite, 50

Byssolite, 104

Acidic rocks, 6

Angstrom, 18

Berrylonite, 55

Bytownite, 94, 97

Actinolite,37, 192

Anhydrite, 43

Beryl, 5, 8, 50

Adamite, 38 Adularescence, 96 Adularia, 95

Anion, 4

green, 51

Cachalong, 140

Anisotropic, 17

synthetic, 220, 230

Cadmium

Ankerite,84

Biaxial, 17

sulfide,

African Star Coral, 70

Anorthite,94,97

Billitonite,

Agalmatolite, 155

Anorthoclase, 93

Birefringence, 17

Calcite,60

Agate, 159

Antigorite, 170

Biron emerald, 220

Agate opal, 140 Akori coral, 70

Apache

Bismuth germanium oxide, 230

Calcium Calcium

tears, 137

Apatite, 44

Alabaster, 60, 108

carbonate, 44

186

Calcentine, 119 fluoride, 230 titanate,

230

Californite, 103, 116

Bismutotantalite, 55

Canasite,61, 181

Alalite,82

Apophyllite, 45

Bixbite, 50, 52

Cancrinite, 61

Albite.94,95

Aquamarine, 50 Martha Rocha, 54

Black opal, 140

Cape

Blende, 175

Carbonate

Carnelian, 159

Alexandrite, 66

230

Cairngorm, 158

series,

79

apatite, 44

Alexandrium, 230

Aragonite,46, 119, 145

Bloodshot iolite, 70 Bloodstone, 159

Algodonite, 39

Arc-imaging, 214

Blue John, 99

Allanite, 88

Asbestos, 171

Bohemian

Almandine, 101,105 Amazonite, 94 Amber, 39 Amblygonite,6,40 Ambroid, 40 Amethyst, 158 Ametrine, 158 Ammolite, 119

Asparagus stone, 44 Atoms, 4

Boleite,56

Bombs

(volcanic), 138

Cation, 4

Attapulgite, 143

Bonds,

4, 16

Catseye,66

Augelite,46

Boracite, 56

Celestite, 62

Australite, 186

Bornite, 56

Centipedes (inclusions), 96

Autoclave, 216

Ceruleite,63

Aventurine, 158

Boulder opal, 141 Boule,214 Bowenite, 170

Chabazite, 64

Chalcedony, 159

Maxixe-type, 52

synthetic, 221

Ammonite

Aventurescence, 97

garnets, 104

Cassiterite, 62

synthetic, 231

Castor, 151

Catapleiite,62

Ceylonite, 177

119

Axinite,47

Brazilianite, 57

Amphibole, 144, 192 Amplitude, 16 Analcime,41 Anatase,41

Azurite,47

Breithauptite, 57

Chalcosiderite, 194

Azurmalachite, 48

Bridgman-Stockbarger method, 213

Chalcotrichite,76

Baddeleyite,224

Brilliance, 16

Andalusite,42

Baikalite,82

Bromellite, synthetic, 230

Chambersite,64 Charoite,65

Andesine,94,96 Andradite,101,104 Angel stone, 143 Angel-skin coral, 70 Angle of incidence, 16 Angle of refraction, 16 Angles (inclusions), 208

Balas ruby, 178

Bronzite, 86

Bananas, 230

Brookite, 58

shell,

Banded

Brucite, 58

Chalybite, 172

Chatham corundum, 222 Chatham emerald, 220

Barite, 49

Buergerite, 189

Checking, 141 Chemical substitution, 5

Basic rocks, 6

Burnite,48

Chert, 159

Bayldonite, 50

Bustamite,58, 163

Chessylite,47

Bediasite, 186

Byon,72

Chiastolite,42

agate, 159

244

INDEX Childrenite, 65, 88

Covellite,75

Diopside, 82

Chiolite, 65

Crazing, 141

Dioptase, 83

Chlorapatite,44

Creedite, 75

Directional properties, 4

Fool's gold, 155

Cristobalite, 158

Dispersion, 3, 17

Critical angle, 16

Djevalite,223

Formanite, 98 Formula, 13

Chondrodite, 113

Crocidolite, 157

Dolomite,

Chroma, 25

Crocoite, 75

Domeykite, 39

Chromdravite, 189 Chrome diopside, 82

Cryolite, 76

Doublet, 142

Chlorastrolite, 153

Chloromelanite,

1

17

Chromite, 66 inelusions,

52

Chrysoberyl,66

axes, 13

140

Forsterite, 137

synthetic, 231

Fracture, 16

Dravite, 189

Francolite,44

Dumortierite,84, 112

Fraunhofer

Fremy

quartz, 158

lines, 17, 18

ruby, 222

Friedelite,99

216

hydrothermal, 215

Chrysoprase, 159

melt, 212

Chrysoltile, 170

solution, 215

CIE system, 26

vapor, 212

Cinnabar, 68

zone, 214

Cinnamon

84

Fuchsite, 158

flux,

quartz, 159

synthetic, 230

growth, 212

214

Chrysocolla, 68

Fluorite,99

emerald, research, 220 edge-defined, film-fed,

synthetic, 221

in

See also Negative

crystal

Chrysanthemum

in opal,

Crystal.

7,

245

Eilat stone, 68

Ekanite, 86 Gadolinite, 101 Elaeolite, 135

Gahnite, 177

Elbaite, 189

synthetic, 231

Electron, 4

Gahnospinel, 177

Emerald, 50

Galaxite, 177 synthetic, 220

Garnet, 101

table of properties, 51 alexandritelike, 106

Enstatite,86 stone, 103

bohemian, 104

opal, 140

Entropy, 211

Citrine, 158

positive, 17

Cleavage,

pulling, 214

15, 16

Cleavelandite,96

rock, 158

Cleiophane, 176

seed, 212

Clinochrysotile, 170

synthetic, characteristics,

Eosphorite, 65, 88

color-change, 105, 106

occurrence, 19

Epidote,88

star,

105

Essonite, 103 synthetic, 225

Ettringite,90

Clinohumite, 113

218

Clinozoisite, 88

structure, 4

Coal, 7

systems, 13

Gas, 4

Euclase,90

Gaylussite, 107

Eucolite,91

Gem

Eudialyte,91 Crystallographic axes, 16

Cobaltite,69

Crystalography, 13

Cobaltocalcite,60

Cubic zirconia (CZ), 215,

Colemanite, 69

definition, 2

Eulite,86

Coarse texture, 6

223

scarcity, 8

Euxenite,92

Gemology, Gemstone,

Evaporite, 7

Extraordinary

1

2

ray, 17

identification, 10

Extrusive rocks, 6

Collector gems, 8

Cultured pearls, 146

Collophane,45

Cuprite, 76

Color, 14

Cybeline, 183

Fairy crosses, 180

sizes of, 19

Geneva

ruby, 211, 222

measurement, 25

Cymophane,68

Faustite, 195

Geologic cycle, 7 Geologic structures, 7

space, 25

Cyprine, 116

Fayalite, 137

Geyserite, 140

zones, 218

Czochralski corundum, 223

Feldspars, 93

GGG,225

Czochralski technique, 214

Fergusonite,98

Gilson emerald, 220

Color-order system, 25 Hunter's, 26

Ferridravite, 189

Girasol, 140

Ferroactinolite,38

Glass, 5, 16

Colorimetry, 25

Damsonite, 159 Danburite, 78

Ferroaxinite,47

Columbite, 185

Darwin

Ferrohypersthene, 86

Goldmanite, 101 Goshenite,50

Colorimeter, 14

glass, 186

Columbotantalite, 128

Datolite,78

Ferropargasite, 144

Grandidierite, 107

Common opal

Demantoid, 104

Ferropumpellyite, 153

Conduction, 20

Dendrites, 212

Ferrosalite, 82

Connemara marble, 170

Density, 15

Ferrotantalite, 128

Gray opal, 140 Green beryl, 51 Green quartz, 158

Consolidation, 7

Derbyshire spar, 99

Fibrolite, 172

Greenockite, synthetic, 230

Contact metamorphism, 7

Detrital sediments, 7

Fine texture, 6

Grossular, 101,103

Contra-luzopal, 140

Diamond, 79

Fire (opal), 140

Gypsum,

,

1

40

Convection, 20 Copal, 40 Coral, 70

probes, 20

Fire agate, 159

synthetic, 224

Diaspore, 81

Flame fusion, 213 Flame opal, 140

108

Hackmanite, 174 Hambergite. 109 Hancockite,88

Diatomaceous earth, 140

Flash opal, 140

Cordierite,70

Dichroism, 18

Flint,

Corundum,

Dickinsonite, 82

Floating opal, 142

Harlequin opal, 140

properties (table), 72

Didymium spectrum, 44

Flowstone, 60

Hartman dispersion

synthetic, 222

Diffraction grating, 11,18

Fluorapatite,44

Dinosaur bone, 159

Fluorescence, 19

synthetic, 222

71

Covalent bond, 4

159

Hardness, 14

18

Hauyne, 109

net, 3,

1

1

INDEX

246

Hawk's-eye, 157

Indicolite, 190

Lenix emerald, 220

Metamorphic

Heat

Indochinite, 186

Lepidolite, 124

Mica, 124

20

transfer,

Heavy

rocks, 6

Intrusive rocks, 6

Lesserite,

Hedenbergite, 82

Inversion, 8

Leucite, 125

Microlite, 130

Helictites, 108

Iolite,

Libyan Desert glass, 186

Microscope. 11,19

Heliodor, 50

Ion, 4

Liddicoatite, 189

Microsommite,61

Heliotrope, 159

Ionic bond, 4

Light absorption, 18

Milarite, 130

Hematine, 110,230

Iris

quartz, 157

Lightness, 25

Milk opal, 140

Hematite, 110

Ironstone opal, 140

Limestone, 7

Milky quartz, 158

Isometric system, 13

Linarite, 125

Millcrite, 130

Isotropic, 17

Linde emerald, 220

Mimetite, 131

Linobate, 230

Mineral, definition,

Liquid, 4

Mineral groups,

liquids. 15

llemimorphite,

1

10

Henritermierite, 102

bloodshot, 70

Hercynite,66, 177 Herderite.

1

Jade, 135, 193

1

Hessonite, 103

1

Microcline.93.94

16

Lithification,7

Mineralizer, 215

reformed, synthetic, 226

Lithiophilite, 193

Mizzonite, 166

Hexagonite, 192

styrian, 170

Lithium fluoride, 231

Mohawkite,39

Hiddenite, 179

synthetic, 225

Lithium niobate, 230

Mohs scale,

H maw-Si t-Sit, Upper Burma,

Transvaal, 103

Lithium tantalate, 230

Moldavite, 186

Yunan, 117

Liver opal, 140

Molecule, 4

Lizardite, 170

Monazite, 131

imperial,

Hexagonal system,

13

117

Hodgkinsonite,

1 1

Jadeite,

1

1

17

17

Lotus leaves (inclusions),

Jasper, 159

Holtite, 112

Homocreate,

3,

217

table, 232

Jasper opal, 140 Javaite, 186

Monoclinic system, 13 6,

Ludlamite, 125

Moonstone, 94

Hornblende, 38, 144

Jeffersonite, 82

Luminescence, 19

Mordenite, 132

Horse-tail inclusions, 104

jeremejevite, 118

Lusakite, 180

Morganite, 50

Howlite. 112

Jet,

Luster, 14

Morion, 158

Hue, 25

Jewel, 2

Mabe

Moss agate, 159 Moss opal, 140

Huebnerite,

118

12

Julgoldite, 153

group, table of properties,

Kammererite,

Humite,

1

1

13

113

Hunter color-order system, 26

1

19

Kashan ruby, 222 Kauri gum, 40 Kidney ore, 155

pearl, 146

1

241

15

Montebrasite,

138

6,

40

Magnesioaxinite, 47

Mountain-leather, mountain-

Magnesiochromite, 66 Magnesite, 127

wood, 144 Mukhinite,88 Munsell system, 25

Magnesium Magnesium

oxide, 231 silicate,

231

Museums

(abbreviations),

20

Hureaulite, 114

Kimzeyite, 102

Majorite, 102

Hurlbutite, 114

Knischka ruby, 223

Malachite, 127

Hyalite, 140

Knorringite, 102

Malacolite,82

Nacre, 146

Hydrogrossular, 102, 103

Koranna stone, 155

Nambulite, 133

Hydrophane, 140

Korite,46, 119

Hydroxylapatite, 44

Kornerupine, 120

Hypersthene,86

Kunzite, 179

Kurnakovite, 120

Malaya, 105 Manganaxinite,47 Manganocolumbite, 128 Manganotantalite, 128 Manganpectolite, 147

Iceland spar, 60

Kutnahorite,84

Mansfieldite, 168

Idocrase, 115

Kyanite, 121

Maori greenstone, 135

inclusions, 52 Neo-noble opal, synthetic,

Kyropoulos technique, 214

Marble, 60

I.

G. Farben emerald, 220

Natrolite, 133

Natromontebrasite, 40 Negative crystal optics, 17

227

Marcasite, 128, 154

Nepheline, 134

Labradorite, 94, 97

Marialite, 166

Nephrite, 135. 192

Lace agate, 159

Marmatite, 176

Neptunite, 136

Impurities, 5, 13, 15

Landerite, 104

Martha Rocha aquamarine,

Niccolite, 137

Inamori emerald, 220

Langbeinite, 122

54

Nicol prism, 17

Inclusions, 19

Lapis lazuli, 123

Matrix opal, 140

Norbergite, 113

Maxixe-type aquamarine,

Normal, 16

Igneous rocks, 6 Illam.73 Imperial jade,

1

17

angles, 208

synthetic, 226

52, 54

centipedes, 96

Larimar, 148

crysanthemum, 52

Laserblue, 231

Mechanical sediments, 7

horse-tail, 104

Lawsonite, 122

Meionite, 166

Nucleation, 212

Nucleus,

4,

211

lotus leaves, 138

Lazulite, 123

Melanite, 104

Obsidian, 137

snow-stars, 52

Lazurapatite,45

Melinophane, 129

Octahedrite,41

spangles, 178

Lazurite, 123

Meliphanite, 129

Odontolite. 199

three-phase, 52

Lechleitner emerald, 220

Mellite, 129

Oligoclase.91,96

zircon haloes, 178

Lechleitner ruby, 223

Menilite, 140

Olivine, 137

Lechososopal, 140

Mesolite, 133

Onyx, 60

Legrandite, 124

Metamict,209

Inderite,

1

16

Index of refraction, 16

silica,

159

4

1

INDEX Polarized rays, 17

Rouge, 110

Opal, 139

Polarizing microscope, 17

Royal Azel,

Optical spectroscope, 18

Pollucitell50

Royal Lavulite, 183

Skutterudite. 173

Po lye rase, 92

Rubellite, 190

Slocum

Polycrystalline aggregate,

Ruby, 71

Slugs, 145

Onyx

Optic

opal, 140

axis, 17

Optics, 16

213

Orbicular jasper, 159

Ordinary

Polysynthetic lamellae, 227

ray, 17

Orient, 145

Positive crystal, 17

Ornamental material, 2

Potassium feldspars, table

Orthorhombic system,

OSA-UCS system,

Sinhalite, 173 18.1

26

stone. 228

Smaltite. 173

synthetic, 227

Smaragdite. 38 Smithsonite, 174

synthetic, 227

Rulillated quartz, 164

Smoky

quartz. 158

Snow-stars (inclusions), 52

Snowflake obsidian, 137

Powellite, 151 13

Skull melting. 214

spinel, 178

Rutile, 163

of properties, 93

Orthoclase,93,95 Orthoferrosilite, 86

Powellite, synthetic, 231

Sagenite, 157, 164

Soapstone, 185

Prase, 159

Salite,82

Sodalite, 174

Samarskite, 165

Sogdianite. 175

40

Oscillators, 227

Prase opal

Oxblood

Precious, 2

Sanidine.93,95

Solid, 4

Precious opal, 140

Sapphire, 71

Solid solution, 13, 15

coral, 70

,

1

247

Padparadscha,71

Prehnite, 151

Painite, 143

Pressed amber, 40

Sapphirine, 165

Solidification. 212

Palygorskite, 143

Properties and structure, 5

Sarcolite, 166

Papagoite, 144

Prosopite, 152, 195

Sard, 159

Sources of data, 13 South African wonderstone.

synthetic, 222

series, 5

Paragenesis, 8

Proton,

Sardonyx, 159

Pargasite, 144

Proustite, 152

Satelite, 170

Spangles (inclusions), 178

Parisite, 144

Pseudomorphs, 140

Satin spar (gypsum), 108

Specific gravity, 11,15

Parrot-wing, 68

Pseudophite, 170

Saturation, 25, 212

Specific heat, 20

Parting, 16

Psilomelane, 110

Scapolite, 166

Spectra, 18

Pastoral opal, synthetic, 227

Pumpellyite, 152

Scenic agate, 159

Spectroscope, 18

Peacock opal. 140

Purpurite, 154

Scheelite, 167

Spectrum, 18

Pearl, 145

Pyralspite, 101

synthetic, 228

155

Spessartine, 101, 106

grain, 146

Pyrargyrite, 154

Schefferite,82

Sphaerocobaltite, 60

Pectolite, 147

Pyrite, 128, 154

Schiller effect, 94

Spalerite, 175

Pentlandite, 148

Pyrope, 101,104

Schorl, 189

Periclase, 148

Pyrophyllite, 155

Schorlomite, 102, 104

Sphene, 176

Pyroxmangite, 155, 163

Scolecite, 133

Spiderweb turquoise, 195

Pyrrhotite, 155

Scorodite, 168

Spinel, 177

synthetic, 231

Peridot, 8, 137

Peristerite,94,95 Perovskite, synthetic, 230

Quartz,

8,

157

synthetic, 227

Perthite,94,95

Scorzalite, 123

alexandritelike, 178

Seam

group, table of properties.

opal, 141

Sedimentary rocks, 7

Seed

Quartzite, 158

Petalite, 148, 151

synthetic, 231

wood, 159

crystal,

212

177 synthetic, 229

Seiko emerald, 220

Spodumene, 179

Selenite. 108

Spurrite. 180

Rarity, 8

Sellaite, 169

Star garnets, 105

Phianite, 223

Realgar, 161

Semiblack opal, 140

Staurolite, 180

Philippinite, 186

Recrystallization,7

Semiprecious, 2

Steatite, 185

Phosgenite, 148

Refractive index, 16

Senarmontite, 169

Stellarite,68

Phosphophyllite, 150

Refractometer,

Serandite, 169

Stibiotantalite. 180

Phosphorescence, 19

Serpentine, 170

Stichtite, 61. 181

Picotite, 177

Regency emerald, 220 Regional metamorphism,

Shattuckite, 171

Stolzite, 181

Picture jasper, 159

Resin opal, 140

Sheen obsidian, 137

Stratification. 7

Piedmontite,88

Rhodizite, 161

Shell agate, 159

Streak, 14

Petrified

Ramaura

Phenakite, 148 synthetic, 231

ruby, 223

1

7

Piemontite,88

Rhodochrosite, 162

Shortite, 171

Strengite, 197

Piezoelectricity, 227

Rhodolite, 102, 105

Siberian amethyst, 158

Strontianite. 182

Pinf ire opal, 140

Rhodonite, 162

Siberian jade, synthetic, 226

Stronitum titanate, 229

Plagioclase feldspars, table

Ricolite, 170

Siderite, 171

Sturmanite,90

Rizalite, 186

Silica, 157

Styrian jade. 170

Rock

Silica glass, 158

Succinite. 39 Sugilite, 182

of properties, 94 Plancheite, 171

crystal, 158

Rocks, 6

Siliceous sinter, 140

Rock-wood, 144

Silicic acid,

Pleochroism, 18

Rodingite, 103

Silicon carbide, 228

Sun spangles (amber), 40

Pleonaste, 177

Sillimanite, 172

Sunstone.94, 98

Plutonic rocks, 6

Rose of France, 158 Rose quartz, 158

Limpsonite, 172

Symmetry.

Polariscope, 17

Rosolite, 103, 104

Simulant, 3

Synthetic, 3, 217

Plasma, 159

Plato-Sandmeier

effect,

222

6

Sulfur. 183

13. 16

1

INDEX

248

Synthetic crystals, characteristics,

218

Synthetic diamond, 217

Transvaal jade, 103

Value, 25

Wollastonite, 203

Trapiche emeralds, 96

Vanadinite, 197

Wulfenite, 203

Travertine, 60

Vapor, 4

Wurtzite, synthetic, 231

Treacle, 103

Variscite, 197

Taaffeite, 184

Tremolite, 38, 192

Vayrenenite, 198

Tabasheer, 140

Trichroism, 18

Talc, 185

Triclinic system, 13

Verde antique, 170 Verneuil corundum, 222

Xalostocite, 104

Tantalite, 185

Tricone burner, 213

Verneuil technique, 213

Xanthite, 116

Tanzanite, 88

Tricone torch, 228

Verneuil torch, 213

Xonotlite-,

Taprobanite, 183

Tridymite, 158

Vesuvianite,

Tawmawite,89

Trigonal system, 13

Victoria stone, 231

Tektite, 186

Trigons, 79

Villiaumite, 199

YAG,225

Tephroite, 186

Triphane, 179

Violane,82

Yamatoite, 102

Tetragonal system, 13

Triphylite, 193

Viridine,42

Yowah

Texture, 6

Triplet, 142

Vishnevite, 61

Yttralox,203

Thaumasite, 187

Tripoli, 140

Viviariite, 199

Yttrium aluminate, 231

Thermal conductivity, 20 Thermal diffusivity, 20 Thermal inertia, 20 Thermal properties, 21

Troostite, 202

Volatile, 212

Trystine, 158

Volcanic glass,

Tsavorite, 103, 104

Vulpinite,43

table, 22

1

X-ray powder diffraction,

1

205

15

nuts, 141

Yugawaralite, 206 6,

137

Yunan jade, 117

Tsialaisite, 189

Tugtupite, 193

Thomsonite, 187 Three-phase inclusions, 52

Turquoise, 194

Thulite,88

TV stone,

Tigereye, 157

Turritella agate, 159

synthetic, 230

196

Wardite,200 Water opal, 140 Water sapphire, 70 Watermelon tourmaline, 189 Wavelength, 16

Tin oxide, 231

Wavellite,200

Tinzenite,47

Weloganite, 201

Zebra

tigereye, 157

Zektzerite, 207

Zerfass emerald, 220

Zinc aluminate, 231 Zinc oxide, 231 Zinc schefferite, 82 Zinc sulfide, 231 Zincite, 207

Titanite, 176

Ugrandite, 101

Wernerite, 166

Topaz, 188

Ulexite, 196

Whewhellite, 201

Topazolite, 104

Ultraviolet light, 19

White opal, 140

Zircon, 208

Torsion balance, 15

Unakite,89

Wilkeite, 201

Zircon haloes (inclusions)

Tourmaline, 189

Uniaxial, 17

Willemite, 202

Unmixing, 94 Uvarovite, 101,102

Williamsite, 170

Zoisite, 88

Wiluite, 116

Zone

Uvite, 189

Witherite,202

Zunyite. 209

bicolor, 189

Tradenames, of synthetic materials, 233

synthetic, 231

178

refining, 214

'1.

ADAMITE:

Ojuela Mine,

Mapimi, Mexico

2.

ALGODONITE: Mohawk

Mine, Keweenaw

Peninsula. Michigan leach -

(0.86)

1

inch across)

4.

AMBER:

Dominican Republic

(with insect inclusion)

3.

AMBER:

All

Baltic Sea area (various cut

numbers

gems and

utility

objects)

refer to carat

weights unless otherwise indicated. Sequential numbers refer to rows of gems, reading left to right, top row, middle rows, bottom row. Rows are separated by double slashes (//).

The symbol

-

means

approximately. The symbol

means

that the

gems

*

illustrated

have been color analyzed and the data appear on pages

28-35. The photos and data can most easily be matched using gemstone color, shape,

and weight.

5.

AMBLYGONITE:

Brazil (5.2,6.3)

*6.

ANDALUSITE:

Brazil

(7.55,2.40,2.92,9.55)

*7.

ANGLESITE: Morocco

(6.99)

8.

APATITE: Catseve

apatite, India

(~ 2.4.5.6)

*9.

APATITE: Burma

(colorless, 7.34),

Mexico (antique, 8.70), Brazil (green, 1.09; blue, 0.86) // Madagascar (light blue, 1.07) Canada (green, 8.05) // Brazil (dark blue, 0.55). Madagascar (light blue, 1.07),

Brazil-? (green, 12.40; dark green, 2.87).

Maine

(violet, 1.02).

10.

1

1.

AUGELITE:

APOPHYLLITE:

California

(

-

1.5,

India (1.3, 8.6, 2.4)

rough

Vj

inch across)

12.

AXINITE: (

13.

ARAGONITE: Czechoslovakia (5.35)

14.

AZURITE Arizona

(

with MALACHITE: Bisbee. - 4 inches high I

Baja California. Mexico /: inches long)

- 2.0, rough

1

l

15.

BARITE: South Dakota

(4.7),

Colorado

(9.4, 1.9)

to

-'-SV'tA*

:

16.

BERYL:

Brazil (yellow, 40.98; green, 18.42; peach, 9.06 // peach, 6.92;

colorless, 11.25; green, 4.54; blue, 18.08 // green, 19.09; pink, 17.33), Africa (blue. 21.80); Brazil (20.00)

*17.

BENITOITE: San

Benito County, California

(1.19,0.66, 1.07// 1.08, 1.15, 1.30)

18.

BERYL: Aquamarine Brazil (18.37)

catseye,

19.

BERYL: Aquamarine,

Brazil

20.

BERYL: Aquamarine.

Nigeria (3.10, 7.82, 2.81)

(25.65)

22.

BORACITE: Germany

*21.

BERYL: Golden

beryl Brazil (20.00, 19.85 // 18.98, 3.20)

23.

BERYLLONITE: Maine

(

-

2,

rough

1

inch across)

Hanover,

(0.6)

25.

BUSTAMITE: Broken New South Wales, Australia (2.6)

24.

BORNITE:

26.

BRAZILIANITE:

'27.

Butte.

Montana (specimens

Brazil (3.0, 2.7)

CALCITE: Paramca, (cobaltian, 3.40).

2 inches across)

Spain

Mexico

(12.55)

28.

29.

CALCITE: Canada

CANASITE: Bur'atskaja, Siberia. USSR I

- 2 inches across)

(600.91]

Urals.

Hill,

30.

CANCRINITF: Bigwood Ontario,

Canada (

Township,

3 inches across)

*31.

32.

CELESTITE: Madagascar

34.

CERULEITE:

(

33.

16.3)

Arizona (specimens each

-

I

CASSITERITE:

Bolivia

CELESTITE: Canada

inch across)

1

(1.5

14.25. 3.5)

35.

CHABAZITE: Nova

Scotia (specimen - 3 inches across)

36.

CHAMBERSITE: Texas

•38.

37.

CERUSSITE: Tsumeb, Namibia

39.

CHIOLITE: Greenland

(1.1)

(0.5)

CHILDRENITE:

Brazil (1.37

(32.87)

40.

CHONDRODITE: New York

(~

2,

Tilly Foster

rough

1

Mine, Brewster.

inch long)

'

CHRYSOBERYL:

42.

Sri

m £

Lanka

(

-

Catseye.

5)

t "**f 43.

CHRYSOBERYL: USSR

Alexandrite,

incandescent

(

-

6):

(above) and daylight (below) "41.

CHRYSOBERYL: Lanka

44.

(

Lanka

(7.80, 6.19, 7.51, 7.04) // Brazil (11.84), Sri

13.25, 9.30 // 21.30), Brazil

CHRYSOCOLLA: (large

Sri

light

(

1

1.49), Sri

Arizona and New Mexico specimen - 4 inches high)

Lanka

(12.02)

*45.

CHRYSOCOLLA: (free form, 13.59)

Arizona

*46.

CLINOHUM1TE: USSR

48.

*47.

CINNABAR: Mexico

(1.52)

COLHMAN1TH:

Boron.

49.

COPAL: New Zealand

California (26.50)

50.

CORAL:

South China Sea (red carving - 4 inches

Charcas,

(1.37)

tall

I

(yellow bead -

1

inch long)

*51.

CORDIER1TE:

Iolite,

India

(1.56,8.51,3.00)

i

„

*52.

CORUNDUM:

Sapphire, Sri Lanka (2.12, 3.76, 4.25, 5.21 // 6.05, 3.60, 4.02, 16.12)

''

>

mm

"53.

CORUNDUM:

Sapphire.

'

'

v

A,

*¥''

Umba

*l-

River, Tanzania

(

1.98, 1.40, 1.86, 3.41. 3.28 // 0.96, 3.77, 1.46, 2.56. 4.64)

v-

v*

*s

;7*?l

"54.

CORUNDUM:

Sapphire.

Montana

(1.35, 1.77, 1.47,

1.66// 1.19, 1.10, 1.40, 1.22, 1.30// 1.03, 1.10,0.96,

0.95, 2.30)

/*&$#& i-* t^i 5

is

.lift*

1

'

>^5v-_

4

0/ 56.

CORUNDUM: (184, in gold

*55.

CORUNDUM: 16.13,

Sapphire. Sri Lanka, heated geuda

3.89// 4.00, 2.21,3.60)

Sapphire. Sri Lanka

pendant with diamonds)

*57.

CORUNDUM:

58.

Ruby, Thailand (3.66),

CORUNDUM:

59.

Burma

(3.56),

Thailand 2.23 // Burma

Ruhr, Thailand (2.22, 3.68. 3.35)

CORUNDUM: Burma

Ruby-Star ruby,

(2.6, 9.62),

India (8.4)

Sri

Lanka

(2.75)

(2.30).

Thailand

(2.1 1. 2.07. 3.56)

60.

CORUNDUM: Sri

Lanka

Sapphire-Star sapphire.

(31.87)

61.

*62.

CREEDITE: Chihuahua, Mexico

CORUNDUM:

Ruby. Burma (gems 0.8-1.3, platinum pin with diamonds)

(().%)

64.

CUPRITE: Onganja. South Africa (48.07)

63.

CROCOITE:

Dundas. Tasmania

(3.4)

in

66.

65.

DANBURITE:

67.

DIAMOND:

Charcas, Mexico

(8.5, crystal

-

2%

DATOLITE: Paterson, New Jersey (4.0)

inches long)

Africa (portion of A. V. Gumuchian's "Spectrum Collection,"

New York

City;

-

l

/i

to 5)

*

68.

DIAMOND:

South Africa;

(rough crystals, - 0.25 to

at sorting office of

DeBeers Co., Kimberley

DIOPSIDE: New York (3.5,

'

DIAMOND:

69.

South Africa

I

5)

*71.

*70.

.

(2.15),

Kenya

(0.75,

chrome

diopside),

DIASPORE:

Turkey (2.10)

USSR

chrome diopside)

72.

DOLOMITE:

Spain

(4.5)

-

2)

ilggiJB 73.

DUMORTIERITE: Nevada Ogilby, California

(

-

1

(- 2 inches across);

74.

*75.

76.

ENSTATITE:

EKANITE:

Sri

Lanka

I

- 0.5)

inch across)

Star enstatite, India

I

- 3 to 15)

ENSTATITE: Kenya Burma 10.55), Kenya

77.

HYPERSTHENE:

(1.80).

(4.38)

Africa

I

- 6)

78.

EPIDOTE: Mexico

Baja California,

(1.0),

Kenya

(1.2)

*79.

80.

CLINOZOISITE: Mexico

(1.18)

II.

ZOISITE: (~ 0.5 to

ZOISITE:

Tanzanite. Tanzania (26.54)

Tanzanite, Tanzania, unhealed, showing natural color range

5)

83.

82.

PIEDMONTITE: Adams (

ZOISITE: ~ 2 inches

Thulite.

Norway (each specimen

across)

County, Pennsylvania

- 4 inches across)

84.

EUCLASE:

Brazil (5.49, 1.34)

85.

FELDSPAR:

Orthoclase, Madagascar (4.98),

Zimbabwe

(1.23), Sri

Lanka

(1.5),

Madagascar

87.

FELDSPAR: Moonstone. and

86.

FELDSPAR: Virginia

1

1

Microcline-amazonite, Amelia Court House, Canada - 2 inches across)

inch); Ontario,

88.

FELDSPAR:

(

Albite, Sri

Lanka

(4.6),

New Mexico

(3.9)

(2.5)

Sri

Lanka

(

- 5 each)

India

89.

FELDSPAR:

Labradorite-'sunstone, "Oregon, showing color range

90.

FELDSPAR:

Labrador! te-

"sunstone,

"Oregon

92.

(

-

1

to 5)

91.

FELDSPAR: Mexico

- 14)

FELDSPAR:

(

Labradorite-'spectrolite, "Finland

(

- 2 inches across)

Labradorite. Chihuahua,

(36.43. 34.0, 24.26)

™* Tta

93.

*'

FELDSPAR:

*

~*?/-

Oli^oclase,

-<*r

Canada

94.

*95.

FLUORITE: Colombia (5.751.

96.

FLUORITE:

FRIEDELITE:

New

(3.96,7.21)

Illinois (1031,

world's largest of this color)

England

Franklin.

Jersey (1.741

(3.05);

Switzerland (0.92),

Illinois

(

15.80) // Illinois

(6.05), Illinois (8.80)

97.

FLUORITE: Africa (62.55), New Hampshire (17.55). New Hampshire (38.10)

(152.90). Illinois

J*

^-'*v>

as* <

'I

Ik *98.

GARNET:

Grossular, Asbestos,

Quebec, Canada

5.01 // 2.59, 4.48, 2.18, 3.88 // 2.47, 4.82. 4.14)

*99.

GARNET:

Malaya. Tanzania (12.80, 11.39, 6.38 // 8.23, 8.56, 14.46)

(9.81),

Tanzania

(4.15,

*100.

GARNET:

Hessonite, Orissa State, India 13.61, 3.81, 5.65)

*101.

GARNET:

Grossular-tsavorite, Tanzania (4.11, 2.47, 1.25, 4.011

102.

GARNET: USSR

103.

GARNET:

Andradite-demantoid,

USSR

(

1.93, 0.93, 4.37)

Andradite-demantoid.

(stones - 0.25-0.50)

«

=

GARNET:

104.

Spessartine, Brazil (4.05),

Amelia, Virginia

(4.65), locality

Madagascar

unknown

107.

GARNET:

GARNET:

Rhodolite.

Tanzania (24.461

GRANDIDIER1TE: Madagascar

106.

*105.

(15.40) //

(6.41)

(1.1

1

108.

HEMIMORPHITE: Mexico

(0.75)

Almandine-

Star garnet, Africa (~15)

m&mL

'

E|m3

.

v %'" *'m

^

t\ /

\;.

*

f

k^tr^^ wL*.^

109.

.

y^L^i

r

HAMBERGITE: Madagascar

(1.5)

1

10.

HEMIMORPHITE:

Zacatecas. Mexico

I

- 3 inches hiuh)

111.

HERDERITE:

112.

HODGKINSONITE: Franklin,

New

Brazil (9.6, 3.65, 9.25)

Jersey

(0.35)

113.

1

14.

HUREAL'LITE: (

HOWL1TE:

California (nodule - 3 inches across)

Pala County. California

- 3 inches across)

115.

IDOCRASE: Africa

118.

1

1.05),

116.

JADE:

Nephrite. China (1.9); Jadeite,

117.

JADE:

Jadeite,

Burma

(2.0)

Africa (2.35), Italy (1.40) // Switzerland (3.80)

JADE: Nephrite and Jadeite,

assorted carvings and beads, China and

USSR

Burma — "imperial

jade" (4.77)

(snuff bottles - 2 inches high)

119.

JADE:

Nephrite. Siberia,

USSR

(owl - 2 inches ta

120.

122.

121.

JADE: Nephrite, China, "chicken-bone jade. Vase Ming Dynasty, 14th century (

- X inches high)

JADE:

Jadeite,

JADE: Chloromelanite, Burma

(

Burma

- 3

(statue - X inches highi

inches long)

*124.

123.

JADE: (pin

Jadeite.

JEREMEJEVITE:

Nerchinsk, Siberia,

USSR

Burma

- 2 inches across)

125.

126.

127.

KORNERUPINE: Kenya

KYAN1TE:

(0.55).

Brazil (4.55, 7.80)

JET: Whitby, England

Madagascar

(1.23),

Kenya

(

~ 3 each)

(1.47)

(0.5,0.4)

*129.

128.

LAZULITE:

LAZURITE: Lapis Lazuli, Afghanistan (solid blue) Chile (mottled), cabochons 5 to 25 carats.

131.

130.

LEGRANDITE: Mexico

(

-

2,

rough

l'/2

MAGNESITE:

LUDLAMITE:

Idaho

i

- 0.5!

inches long)

133.

132.

Brazil (0.70.0.441

MALACHITE:

Brazil (134.5, world's largest cut magnesite)

134.

MANGANOTANTALITE: Alta Ligonha.

Mozambique

(5.5)

Zaire

I

- 4 inches high

I

135.

COLUMBOTANTALITE:

136.

Brazil (2.9)

*138.

MICROLITE:

Brazil (0.14)

139.

ST1BIOTANTALITE: Mozambique (1.0)

MILARITE: Tsumeb, Namibia

141.

OBSIDIAN: Mexico (banded and sheen

varieties);

(0.53)

137.

MELLITE: Germany

140.

MIMETITE: Tsumeb. Namibia

Utah ("snowflake obsidian," cabochon 30

<

40

(2.81)

mm)

(0.42)

142.

NATROLITE: Bound

Brook,

New

Jersey (~5)

143.

NICCOLITE: cabochon -

145.

1

OPAL: Semiblack (

144.

OPAL: Black

opal, Australia (free-form

cabochons - 30 carats each)

146.

OPAL: Black

opal, Australia (stone in bracelet

- 20 carats)

Cobalt, Ontario, inch long)

- 10 carats)

Canada

(polished

opal, Australia

147.

OPAL: Black

opal, Australia,

lighting position

#1

(stone in ring - 10 cts)

148.

OPAL:

Triplet,

Australian rough,

ceramic base/quartz top (30 x 23 mm) "149.

OPAL:

Fire opal. Idaho (11.74),

Mexico (5.15, hyalite) Mexico (0.76, 8.04)

//

150.

OPAL:

Contraluz, Mexico, illuminated

from front (~-4)

151.

OPAL:

Contraluz - 4)

from rear

(

Mexico, illuminated

1

152.

OPAL: Black

154.

PEARL: Worldwide

156.

PECTOLITE:

opal, Australia, lighting position

localities, selected to

"Larimar,

#2 (stone

show color

in ring

153.

OPAL: Moss

155.

PERIDOT: Burma

opal,

Idaho

- 10 cts)

variation.

"Dominican Republic (cabochons

- 6 to 30 carats)

(83.01

(5.70)

•157.

158.

PETALITE:

PERIDOT: Norway

(4.51),

Egypt

(8.22) //

Arizona

(9.20, 8.25)

Brazil (15.65)

159.

PHENAKITE: Colorado

(stone

~

2.5)

160.

PHOSGENITE: Monte

Poni,

161.

PHOSPHOPHYLLITE:

Potosi, Bolivia (8.1

Sardinia (1.5)

=

162.

POLLUCITE: Maine (gem

164.

PREHNITE: Mexico

- 2

163.

PROUSTITE: Germany

cts)

(2.47), Australia (7.65)

165.

PUMPELLYITE: Isle Royale, Lake Superior. Michigan (pebbles - 'A inch

I

(7.53)

166.

167.

PURPURITE:

Usakos, Namibia (specimens - 2 inches across)

PYROXMANGITE: Japan

169.

468.

QUARTZ:

Brazil (colorless, 11.0; green, 4.48; rose, 14.20)

(0.55)

QUARTZ:

Citrine, Brazil (7.55,4.20,8.81. 12.64 // 16.90, 19.72, 15.76)

171.

=

170.

QUARTZ: Smoky

QUARTZ:

with inclusions, Brazil (dendrites, tourmaline, - 6, 12, 25, respectively)

Quartz. Brazil (23.78),

15.61 //9.37, 13.57)

*172.

QUARTZ:

Amethyst, Brazil (6.22, 9.18), Zambia (8.52) // Brazil (4.40, 3.61. 6.41, 6.38)

173.

QUARTZ:

Chrysoprase, Australia beads - 8 mm)

(largest

rutile.

"

174.

QUARTZ:

"Ametrine,

Uruguay

{- 15,25)

175.

QUARTZ: (slab

176.

QUARTZ:

177.

QUARTZ: Jasper,

Jasper, southwestern

(cabochon - 30

<

Agate, Mexico, "fortification agate" ~ 4 inches across)

United States (cabochons ~ 30 x 40

Oregon, "picture jasper" 40 mm I

mm)

178.

179.

QUARTZ:

QUARTZ:

Tigereye, South Africa (rough

Petrified

Wood. Utah

mass - 3 inches long:

(slab - 4 inches across)

180.

REALGAR:

182.

RHODIZITE: Madagascar

Washington

(0.65)

blue and red cabochons are dyed)

181.

RHODOCHROSITE: stalactite, with

Argentina, cross-section of > 20 mm)

cabochons (15

(0.491

*183.

1X4.

RHODOCHROSITE:

RHODONITE: mm)

Peru

17.15),

South Africa

Australia

185.

(9.42),

RHODONITE: New

(beads, 15

*187.

SCAPOLITE:

Argentina (3.95)

Broken Hill. South Wales, Australia

Tanzania (32.44, 32.00)

186. (4.5)

SARCOLITE:

Italy (0.33)

*188.

SCAPOLITE:

Tanzania (14.83)

189.

SCAPOLITE: scapolite.

190.

*191.

SCHEELITE:

California (2.2).

Mexico

Catseye

Burma

(7.0)

(2.4)

SCORODITE: Tsumeb, Namibia (1.15, 1.50)

192.

SERANDITE: (

Mt.

Ste. Hilaire.

- 1.5, rough - 2 inches long)

Quebec. Canada

193.

194.

SERPENTINE:

SERPENTINE, Maryland

Pakistan

(

Williamsite,

196.

SIDERITE:

198.

SIMPSONITE:

Portugal (1.40)

(2.3)

195.

197.

- 4 inches long)

SILLIMANITE:

Fibrolite,

Kenya

SHORTITE: Wyoming

(0.34),

Burma

(2.44)

(0.5)

Brazil (0.27)

s

•199.

SINHALITE:

Sri

Lanka

(4.58. 7.07 // 4.18. 9.18)

*200B.

SMITHSONITE: Tsumeb, Namibia (8.00, 10.40)

200A.

SMITHSONITE: Tsumeb, Namibia (cabochon faceted

gems -

201.

- 50,

18, 12)

SMITHSONITE:

Kelly Mine.

New Mexico

(blue 5 inches).

Mexico (other

colors)

202.

SODALITE: Namibia

203.

HACKMANITF:

*205.

(

- 2 each)

Ontario.

Canada

(0.8, 4.7)

SPHALERITE: Colorado

(

1.931.

204.

SPHALERITE:

Spain (3.30), Mexico (4.65)

Spain

Spain (14.48. 5.57)

(

- 6)

206.

SPHENE:

Baja California, Mexico (6.0, 6.4, 6.75)

207.

SPINEL, Gahnite,

Brazil

(1.56)

*208.

SPHENE: Madagascar

(6.22),

(1.01, 1.44, 4.22), India (2.65)

Baja California, Mexico (1.55.

1.76). India (7.01) //

Baja California, Mexico

209.

SPINEL: Burma (

2 to 15)

•210.

SPINEL: //

USSR

Sri

Lanka

(8.21, 7.65),

(6.56, 8.87),

Burma

Burma

(11.40)

(5.23) // 9.02, 7.07, 5.89

•211.

SPINEL:

*212.

Sri

Lanka

SPINEL: Burma

(8.35, 9.20, 9.30.

(5.30, 2.98

3.07 // 2.34, 10.98, 3.95 // 8.89, 2.68, 3.21

15.22// 4.78, 11.23,7.27,5.46,3.96// 11.98,8.53,7.98, 14.961

*213.

214.

SPODUMENE:

SPODUMENE:

Brazil (29.85), Afghanistan

Triphane, Pakistan, (~ 170)

(

16.06, 32.71) // California

215.

(

17.76),

Afghanistan

SPODUMENE:

(

17.01

1,

Brazil (47.33)

Kunzite, Brazil (720)

217.

STRONTIANITE:

Austria

(2.1)

216.

STICHTITE: Argent Hill, Tasmania, Australia (specimen - 2 inches across)

M HmEsk

w* I

•,. .

:

v-

-,j->; vA

9

*''

"""•

If

**** 1 fe

'

219.

TEKT1TE:

Moldavite, Czechoslovakia

:

(6.4)

1

1

218.

SUGILITE: Kuruman, South

Africa (gem 3.66)

220.

TAAFFEITE: (1.17, 1.52)

221.

THOMSONITE: New Mexico Lake Superior. Michigan

I

-

V2

(cabochon 23 - 47 mm), inch each, rough stones)

Isle

Royale,

Sri

Lanka

*222.

*223.

TOPAZ: USSR,

TOPAZ: USSR USSR (17.84)

'imperial topaz"

225.

(

(6.72), Brazil (12.59),

224.

17.84)

TOPAZ:

Mexico

(5.29), Brazil (4.65) // Brazil (25.25, 8.76, 7.20, 8.45),

TOPAZ:

Blue topaz, "London Blue," and heated - 8 each)

irradiated

(

Blue topaz, irradiated and heated (~ 115)

4g&*®? vJT>,

48k

*226.

*227.

TOURMALINE: Mozambique

TOURMALINE:

Rubellite,

<^ Irk?

(color suite, 1.81-3.08)

Madagascar

(36.85). Brazil (13.16, 17.13 // 16.73, 10.26, 23.56)

A

1

*22
TOURMALINE: 1

10.05.

"229.

Brazil (9.84, 15.96), Africa

chrome), Brazil

*230.

TOURMALINE,

*231.

(21.32)

(

10.90),

(5.74, 5.84 // 10.39, 46.84)

Bicoloi; Brazil (4.92, 23.90, 14.32)

TOURMALINE: (10.95).

TOURMALINE: Mozambique Tanzania

(9.68, 14.75)

Afghanistan (23.32), Brazil

Mozambique

1

1.13). Pala. California

232.

TOURMALINE:

Catseye

tourmaline. Brazil (20.85)

233.

TOURMALINE,

234.

TREMOLITE: (~

1.

crystal -

Watermelon tourmaline.

Hexagonite, Balmat, 1

Brazil (large slice -

1

inch across)

New York

inch long)

235.

TUGTUPITE: (specimen -

236.

1

Illimassauk, Greenlanc inch acrossl

TURQUOISE: New Mexico

Arizona and

(right-rear

nuggel - 2 inches long)

1

237.

TURQUOISE:

239.

*240.

Iran,

matched beads (

WILLEMITE:

15

Franklin,

WELOGANITE:

Francon Quarry,

Quebec, Canada

(0.37)

238.

mm)

New

241.

VARISCITE:

Fairfield,

Utah

(slab - 6 inches

across)

Jersey (0.5, 6.94, 0.6)

WITHERITE:

England

(1.89)

242.

WULFENITE: Tsumeb, Namibia (21 +

243.

WULFENITE:

Arizona (gem -

1.5, crystal

1

inch long,

Red Cloud Mine) 244.

ZINCITE:

246.

XONOTLITE: Italy

245.

*247.

ZIRCON: Cambodia

ZIRCON: (5.56) // Sri

(

(gems -

- 25, 40 carats)

Lanka (14.03, Lanka (8.92. 16.63,

Sri

Franklin,

17.43, 14.20, 9.26 // 4.36, 11.26, 15.70),

7.77, 5.34)

Cambodia

New

Laghi

Jersey (gem -

di Posina,

2 carats each)

1.

rough 2 inches longl

Vicenza,

248.

ZIRCON:

Sri

Lanka (blue

= Cambodia)

(

- 3-30 carats)

SYNTHETICS \Note:

The photographs

of synthetic

gemstones are purposely numbered beginning with 301

to distinguish

them from the

gemstones.]

302.

VERNEUIL RUBY: - 2 inches long

301.

VERNEUIL PROCESS:

Boules grown by A. Verneuil and

associates ~ 1900: upright boule

Vi

inch.

largest boule

natural

(O-

304.

CHATHAM RUBY: crystal -

303.

CORUNDUM GEMS:

305.

RAMAURA RUBY:

all

gem

8

•

10

307.

largesl

inch

mm

- 5 carats, crystals

306.

- 2 inches across

&

'/?

CHATHAM

SAPPHIRE: hexagonal

- 3 inches across

9 Q

STAR CORUNDUM: cabochons

8

10

mm,

"Heller

Hope"

stars.

crystal

308.

CHATHAM SYNTHETICS: size (green heart

309.

CHATHAM EMERALD:

is

corundum, various

colors, - 3-5 carat

synthetic emerald)

largest crystal - 2 inches long

310.

INAMOR1 SYNTHETICS:

all

- 2 carats, ruby,

alexandrite // emerald, sapphire

312.

GILSON EMERALD: very large crystal,

311.

GILSON OPAL:

cabochons - 3-6 carats

437 carats, - 60 x 40 X 10

mm

314.

REGENCY EMERALD: gem

2.88 carais.

crystal 20.25 carats

313.

GILSON LAPIS, TURQUOISE:

blocks, lapis 94.4 carats,

turquoise 96.5 carats

316.

315.

SLOCUM STONE:

blocks -

'/

2

&

crystals

grown by G.E. process

T*

*$?

ISJ

GENERAL ELECTRIC SYNTHETIC DIAMOND:

inch square

o 317.

CUBIC ZIRCONIA: various colors, - 1-15 carats

319.

STRONTIUM TITANATE: marquise - 25 carats

318.

YAG:

320.

SYNTHETIC SPINEL:

various colors, 3.3 to 13.3 carats

all

8

10

mm

321.

RL1TILE: emerald-cut. 7.84 carats

322.

RUTILE:

color suite.

1.45 to 7.25 carats

324.

SYNTHETIC BLUE QUARTZ: 14.80 carats

323.

SYNTHETIC QUARTZ:

(USSR)

amethyst (6.13, 10.451

citrine (22.80)

326.

SYNTHETIC GARNETS: yttrium-aluminum-gallium-

doped with chromium (dark green), gem = 1»4 carats

garnet,

325.

SYNTHETIC GARNETS: yellow = dysprosium= neodymium-gallium: all 1-5 carats.

aluminum: orange

—

samarium-

gallium: red

328.

SAMARIUM GALLIUM GARNET:

327.

GGG:

rounds, - 2-15 carats

6.19 carats

330.

BARIUM TUNGSTATE: - 3 carats

329.

LITHIUM NIOBATE:

rounds, - 10, 15 carats

332.

BISMUTH GERMANIUM OXIDE:

331.

LITHIUM TANTALATE:

333.

rounds, -

6, 15 carats

CADMIUM SULFIDE (GREENOCKITE):

10.80 carats

~ 5 carats

334.

BARIUM SODIUM NIOBATE - 4-5 carats

("bananas"

335.

CADMIUM SELENIDE (50-50)/ CADMIUM SULFIDE (25-731: - 5 carats

336.

TELLURIUM OXIDE (TELLURITE):

8.10 carats

337.

LEAD MOLYBDATE (WULFENITE):

339.

~ 8 carats

MAGNESIUM OXIDE (PERICLASE): doped with nickel, - 5 carats

338.

LEAD MOLYBDATE (WULFENITE): 84»

carats

340.

342.

343.

(SANMARTINITE):

SILVER ARSENIC SULFIDE (PROUSTITE)

- 3 carats

6.98 carats

ZINCTUNGSTATE

341.

CALCIUM TUNGSTATE (SCHEELITE): gems

LASERBLUE":

16.(14.

11.30

- 3-15 carats

344.

ALEXANDRILM":

30.40 carats

(Continued from front flap)

measurements on a wide range of cok gemstone species and varieties. Machine color analysis is far more accurate than visual estimation in gemstone description, and this is the first work ever to present this kind of information.

A

section on thermal properties of

introduces you to this

new and

gems

potentially

useful diagnostic tool. In addition, the Encyclopedia puts at your fingertips:

"mini-course"

•

a

•

an

"at-a-glance"

in physical

geology;

summary of

minerals

with similar structures;

and species indices;

•

refractive

•

a periodic table of the elements;

•

and much more.

With the

clarity

and depth of

its

coverage,

Color Encyclopedia of Gemstones, Second Edithe most comprehensive work

tion, is truly

of

its

kind

now

available. It

reference tool for anyone

gems

is

Joel E.

with

anyone interested more about them.

as well as for

learning

an essential

who works

Arem

in

received the B.S. degree in

geology from Brooklyn College, and the

M.A.

in

geology and Ph.D.

in

mineralogy

from Harvard University. He is generally recognized as one of the world's foremost experts on colored gemstones. He is the author of four books and numerous popular

and technical articles on gems, minerals, and crystals. In addition, he is an awardwinning jewelry designer, the first American ever to win the prestigious Tully Memorial Medal of the Gemmological Association of Great Britain, and for three years was president of the Accredited Gemologists Association. He is the president of his own gemstone marketing firm, and resides in Gaithersburg, Maryland.

VAN NOS HRAND REINHOLD COMPANY

VAN NOSTRAND REINHOLD COMPANY 115 Fifth Avenue,

New

York, N.Y. 10003

ISBN 0-MM2-20fi33-a