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Summer 1982 Gems & Gemology

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Summer 1982 Gems & Gemology '01 UME XVIII SUMMER 1982 ¥^i The quarterly journal of the Gemological Institute of America I "-1, \.. SUMMER 1982 Volume 18 Number 2 TABLE OF CONTENTS FEATURE 62 Sri Lanka: The Gem Island ARTICLES Peter C. Zwnan The Identification of Artificial Coloration in Diamond Kenneth V. G. Scarratt Heat Treating Corundum: The Bangkok Operation Jack S. D. Abraham NOTES 83 Pinpoint Illumination: A Controllable System of Lighting for Gem Microscopy AND NEW John I. Koivula TECHNIQUES 8 7 Radioactive Irradiated Spodumene George R. Rossman and Yuanxun Qiu Tugtupite: A Gemstone from Greenland Aage Jensen and Ole V. Petersen Carving Gem-Quality Opal Theodore Grussing Two Notable Color-Change Garnets Carol M. Stockton REGULAR Gem Trade Lab Notes FEATURES Editorial Forum Gemological Abstracts Book Reviews , Gem News ABOUT THE COVER: Cat's-eye chrysoberyl is one of many fine gemstones found on the island of Sri Lanka, the subject of Peter Zwaan's article in this issue. This fine 9.57-ct cabochon from Sri Lanka is pictured here against a 19th century lithograph by Dr. von Kurr of a twin chrysoberyl crystal. This stone, part of the Hixon Collection, is at the Los Angeles County Natural History Museum. Photograph "J 1978 Harold and Erica Van Pelt- Photographers, Los Angeles, CA. Composition for Gems & Gemology is by Printed Page Graphics, Fullerton, CA. The color separations are by Effective Graphics, Compton, CA. Printing is by Waverly Press, Easton, MD V982 Gemological Institute of America. All rights reserved. ISSN 001 6-626X ~OCUS "Gems EXPANDS YOUR RESOURCES! AS A PROFESSIONAL AS AN INSTRUCTING AS AN AUTHORITY IN SALESPERSON EMPLOYER YOUR COMMUNITY you increase customers' confidence you train employees rapidly in the you present talks on gem sources, in your expertise as you expand their selling points of gemstones and how mining, culturing, and cutting with interest and involvement in gemstones to separate natural from synthetic groups of customers and potential with illustrations of inclusions in nat- corundum, opal, alexandrite, and customers. ural stones such as ruby. emerald. spinel, as well as diamonds from and sapphire. simulants. This exciting concept in aids consists of 12-35rnrn slides on inclusion/ identification or gem localities, plus descriptive ~ext.The packages are sturdy 7 x 9-1/4-inch fold- ers. Add these important references to your gemological library! $22.50 per slide set Inclusion/Identification Major Gem Locations Slide Sets: and Production: Natural Emerald Muzo, Colombia-the Mining Synthetic Emerald of Emeralds Gemstones and Their Phenomena Gem Deposits of South-East Natural Ruby Kenya Synthetic Flux Ruby Gem Mining in Sri I,anka: Katnapura and Elehara Freshwater Cultured Pearls of Synthetic Flame Corundum Lake Biwa, Japan Gem Production: Chantaburi, Natural Blue Sapphire Thailand Gem Cutting of Idar-Obcrstein Opal and Synthetic Opal Goober Pedy, Australia-the Diamond Cutting Diamond Simulants Mining of Opals Gem Pegmatites of Brazil Green Jade and Jade Simdants ToLlrl,, aline Deposits of Synthetic Alexandrite San Diego, California Natural and Synthetic Spinel hsand ~i~~~~l~of Sari Diego, ^¥EA~oobto California - parts I and I1 1735 Stewart Street P.O. Box 2052 Gem Pegmatites and Their Santa Monica, CA 90406 Pockets of San Diego, California Tel.: (213) 824-3126 Saltwater Cultured Pearls of Ago Bay, Japan EDITORIAL Editor-in-Chief Managing Editor Editor, Gem Trade Lab Notes STAFF Richard T. Liddicoat, lr. Alice S. Keller Chuck Fryer 1660 Stewart St. Associate Editor Editor, Gemological Abstracts Santa Monica, CA 90404 Peter C. Keller Dona M. Dirlam Telephone: I2131. , 829-2991 Associate Editor Subscriptions Manager Editor, Book Reviews D. Vincent Manson Janet M. Fryer Michael Ross Contributing Editor Editorial Assistant Editor, Gem News John I. Koivula Sally A. Thomas Stephanie -Dillion PRODUCTION Art Director Cover Design GIA Photographers STAFF Susan Kingsbury Peter Johnston Mike Havstad Tino Hammid EDITORIAL Robert Crowningshield C. S. Hurlbut, Jr, Kurt Nassau REVIEW BOARD New York, NY Cambridge, MA Bernfirdsville, N/ Pete Dunn Anthony R. Kampf Glenn Nord Washington, DC Los Angeles, CA Los Angeles, CA Dennis Foltz Robert E. Kane John Sinkankas Santa Monica, CA Los Angeles, CA Sun Diego, CA Chuck Fryer John Koivula George Rossman Santa Monica, CA Santa Monica, CA Pasadena, CA Sallie Morton San lose, CA SUBSCRIPTIONS Subscriptions in the U.S.A. arc priced as follows: $19.50 for one year (4 issues], $52.50 for three years (12 issues]. Subscriptions sent elsewhere are: $28.00 for one year, $75.00 for three years. Special annual subscription rates are available for all students actively involved in a GIA program: $15.00 U.S.A., $23.50 elsewhere. Your student number must be listed at the time your subscription is entered. Single issues may be purchased for $6.00 in the U.S.A., $8.00 elsewhere. Discounts are given for bulk orders of 10 or more of any one issue. A limited number of back issues of G&G are also available for purchase, Please address all inquiries regarding subscriptions and the purchase of single copies or back issues to the Subscriptions Manager. MANUSCRIPT Gems a) Gemology welcomes the submission of articles on all aspects of the field. Please see the Suggestions for SUBMISSIONS Authors for preparing manuscripts in the Summer 1981 issue of the journal or contact the Managing Editor for a copy. Letters on articles published in Gems a) Gemology and other relevant matters are also welcome. COPYRIGHT Abstracting is permitted with credit to the source. Libraries are permitted to photocopy beyond the limits of U.S. copyright law for private use of patrons. Instructors are permitted to photocopy isolated articles for noncommercial AND REPRINT classroom use without fee. For other copying, reprint, or republication permission, please contact the Managing PERMISSIONS Editor. Gems a) Gemology is published quarterly by the Gemological Institute of America, a nonprofit educational organization for the jewelry industry, 1660 Stewart St., Santa Monica, CA 90404. Any opinions expressed in signed articles are understood to be the views of the authors and not of the publishers. SRI LANKA: THE GEM ISLAND By Peter C. Zwaan Sri Lanka, formerly Ceylon, remains one he gem riches of Sri Lanlza have been legendary for of the single most important sources for T centuries. One of the earliest descriptions is that of fine gemstones. Especially notable are Nearchus, who in 334 B.C. mentioned an island not far blue sapphire, pink sapphire or ruby, and from Persia where beautiful translucent gems had been yellow sapphire; alexandrite and cat's-eye found. Without a doubt, this island was the present Sri chrysoberyl; and almandite and hessonile Lanlza. Much later, at the beginning of the 16th century, garnet. Spinel, tourmaline, zircon, Portuguese sailors discovered the island and returned to moonstone, and quartz are also relatively common; they share their country of Europe with some of its gemstones; seamen from Holland origin with several rarer gemstones as did the same some hundred years later. well. Most of the gem-quality material is Over the centuries, tens-probably hundreds-of found in alluvial deposits throughout the thousands of carats of fine sapphire, ruby, chrysoberyl, island, which are mined by primitive spinel, and other familiar as well as unusual gemstones methods. In many instances, the Sri have been mined in Sri Lanka. Yet many questions con- Lankan origin of the gemstone can be tinue to surround the geology of the deposits, and mining determined by characteristic inclusions, methods remain, for the most part, very primitive. several of which are also discussed in During the course of the author's eight trips to Sri this article. Lanlza, he has traveled all over the country and inspected the major mining areas-beginning in 1958 with the his- torically important Ratnapura area and completing most recently, in February and November of 1981, a study of the newer Tissamaharama area. The author has drawn from his experiences and in- vestigations to provide this overview of the geology of Sri Lanlza and its mining and cutting practices, as well as spe- -- -- cial features of the various gem materials found there. ABOUT THE AUTHOR Also examined are inclusions characteristic of Sri Lankan Professor Zwaan is director of the National gemstones and production figures for the area. Museum of Geology and Mineralogy, Leiden, Netherlands. GEOLOGY Acknowledgments: The author is much indebted to Mr. W. A. M. Devil@,photographer of the Sri Lanka is one of the most important localities for gem- National Museum of Geology and Mineralogy at stones in the world. Almost all of these gems, however, Leiden, for the preparation of figures 3, 6, 11, 12, occur in alluvial deposits, and their original source re- 13, and 14. mains unknown today. This article was developed from a paper A geologic slzetchmap (figure 1)shows that the island presented at the International Gemological Symposium in Los Angeles, California, is almost entirely underlain by Precambrian roclzs. These February 1982. roclzs can be divided into threegroups based on their lith- '1982 Gemological Institute of America ology, structure, and age, as described below. 62 Sri Lanka GEMS & GEMOLOGY Summer 1982 SRI LANKA Figure 1. Geological sketchmap of Sri Lanka, with the main gem- producing areas identified. CENOZOIC PRECAMBRIAN Meetiyagod HIGHLAND GROUP Galle¥ VIJAYAN COMPLEX The oldest unit on the island is the Highland amphibolite facies, such as biotite-hornblende group, which contains rocks of the metamorphic gneisses. granulite facies, such as hypersthene gneisses The overlying Southwest group consists of (charnoclzites),sillimanite-garnet gneisses (lzhon- roclzs that belong to the cordierite-granulite dalites), biotite-garnet gneisses, and marbles in facies. It contains both cordierite gneisses and which forsterite and spinel occur. Most of the khondalites. gem deposits are located within this group. Although most of these roclzs, as well as nu- The second unit is the Vijayan complex.
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