G EMS & G VOLUME XLVII WINTER 2011 EMOLOGY W INTER 2011 P AGES 259–336 Dyed Purple Ethiopian Opal Garnet Composition from Gem Properties Symmetry Boundaries for Round Brilliants V OLUME Odontolite in Antique Jewelry Safety of Irradiated Blue Topaz 47 N O. 4 THE QUARTERLY JOURNAL OF THE GEMOLOGICAL INSTITUTE OF AMERICA Winter 2011 Volume 47, No. 4 ® EDITORIAL 259 Great Expectations Jan Iverson FEATURE ARTICLES 260 Dyed Purple Hydrophane Opal Nathan Renfro and Shane F. McClure Carat Points Evidence indicates that opal with a vivid purple bodycolor, reportedly from a new deposit in Mexico, is actually dyed hydrophane from Ethiopia. 272 Determining Garnet Composition from Magnetic Susceptibility And Other Properties Donald B. Hoover Garnet compositions derived from measurements of physical properties pg. 262 correspond closely with results obtained using chemical data. 286 GIA’s Symmetry Grading Boundaries for Round Brilliant Cut Diamonds Ron H. Geurts, Ilene M. Reinitz, Troy Blodgett, and Al M. Gilbertson GIA’s boundary limits for 10 symmetry parameters, measured by optical scanners, will improve consistency in the symmetry grading of round brilliants. NOTES & NEW TECHNIQUES 296 A Historic Turquoise Jewelry Set Containing Fossilized Dentine (Odontolite) and Glass Michael S. Krzemnicki, Franz Herzog, and Wei Zhou Investigation of six antique brooches identifed most of their “turquoise” cabochons as odontolite. pg. 287 RAPID COMMUNICATIONS 302 The Radioactive Decay Pattern of Blue Topaz Treated by Neutron Irradiation Jian Zhang, Taijin Lu, Manjun Wang, and Hua Chen Some “London Blue” topaz contains radioactive trace impurities that may require several years to reach a safe level. REGULAR FEATURES 308 Lab Notes Fancy Vivid purple diamond • Strongly purple-colored black diamond • HPHT-treated diamond with the fluorescence pattern of an HPHT-grown synthetic • Type IIb diamond with long phospho- rescence • Clarity-enhanced opal with artificial matrix • Ethiopian black opal • Coated bead-cul- tured freshwater pearls • Tenebrescent zircon 316 Gem News International Chondrodite from Tanzania • Blue dolomite from Colombia • Fluorite from Namibia • Common opal from Western Australia • A bicolor, bi-pattern hydrophane opal • Chatoyant quartz with cinnabar inclusions • Quartz with acicular emerald inclusions • Quartz with izoklakeite inclusions • Ruby and pg. 312 sapphire mining in Pakistan • Color-change sphene from Pakistan/Afghanistan • Cobalt blue– colored spinel from Vietnam • Trapiche spinel from Mogok, Myanmar • Non-nacreous “cat’s-eye pearls” • Large synthetic quartz • Sugar-acid treatment of opal from Wollo, Ethiopia • Conference reports 336 Book Reviews/Gemological Abstracts Online Listing www.gia.edu/gandg EDITORIAL Editor-in-Chief Editor and Technical Specialist Associate Editor STAFF Jan Iverson Brendan M. Laurs Stuart D. Overlin [email protected] [email protected] [email protected] Senior Manager, Editor, Gemological Abstracts Editors, Lab Notes Communications Brendan M. Laurs Thomas M. Moses Amanda Luke Shane F. McClure Editor, Gem News Contributing Editor Editors, Book Reviews International James E. Shigley Susan B. Johnson Brendan M. Laurs Jana E. Miyahira-Smith Circulation Coordinator Editor-in-Chief Emeritus Martha Rivera Alice S. Keller (760) 603-4000, ext. 7142 [email protected] PRODUCTION Art Director Image Specialist G&G Online: STAFF Nanette Newbry Kevin Schumacher gia.metapress.com Studio 2055 EDITORIAL Ahmadjan Abduriyim Emmanuel Fritsch Robert E. Kane Kenneth Scarratt Tokyo, Japan Nantes, France Helena, Montana Bangkok, Thailand REVIEW BOARD Shigeru Akamatsu Jaroslav Hyršl Lore Kiefert James E. Shigley Tokyo, Japan Prague, Czech Republic Lucerne, Switzerland Carlsbad, California Edward W. Boehm A. J. A. (Bram) Janse Michael S. Krzemnicki Christopher P. Smith Chattanooga, Tennessee Perth, Australia Basel, Switzerland New York, New York James E. Butler E. Alan Jobbins Thomas M. Moses Wuyi Wang Washington, DC Caterham, UK New York, New York New York, New York Alan T. Collins Mary L. Johnson Mark Newton Christopher M. Welbourn London, UK San Diego, California Coventry, UK Reading, UK John L. Emmett Anthony R. Kampf George R. Rossman Brush Prairie, Washington Los Angeles, California Pasadena, California SUBSCRIPTIONS Copies of the current issue may be purchased for $29.95 plus shipping. Online subscriptions are $74.95 for one year (4 issues). Combination print + online subscriptions are $139.95 in the U.S. and $160 elsewhere for one year. Canadian subscribers should add GST. Discounts are available for group subscriptions, renewals, GIA alumni, and current GIA students. For institutional rates, contact the Associate Editor. Subscriptions include G&G’s monthly gemological e-newsletter, the G&G eBrief. To purchase subscriptions and single issues (print or PDF), visit store.gia.edu or contact the Circulation Coordinator. PDF versions of individual articles and sections from Spring 1981 forward can be purchased at gia.metapress.com for $12 each. Visit gia.edu/gandg for free online access to the 1934–2010 subject and author index and all 1934–1980 issues. Gems & Gemology’s five-year impact factor (for 2005–2009) is 1.737, according to the 2010 Thomson Reuters Journal DATABASE Citation Reports (issued June 2011). Gems & Gemology is abstracted in Thomson Reuters products (Current Contents: COVERAGE Physical, Chemical & Earth Sciences and Science Citation Index—Expanded, including the Web of Knowledge) and other databases. For a complete list of sources abstracting G&G, go to gia.edu/gandg. MANUSCRIPT Gems & Gemology welcomes the submission of articles on all aspects of the field. Please see the Guidelines for Authors at SUBMISSIONS gia.edu/gandg or contact the Editor. 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Postmaster: Return undeliverable copies of Gems & Gemology to GIA, The Robert Mouawad Campus, 5345 Armada Drive, Carlsbad, CA 92008. Our Canadian goods and service registration number is 126142892RT. Any opinions expressed in signed articles are understood to be opinions of the authors and not of the publisher. ABOUT The recent appearance of purple play-of-color opal, reportedly from a new deposit in Mexico, has heightened interest in THE COVER the origin and nature of this material. In this issue, Nathan Renfro and Shane McClure offer gemological and spectro- scopic evidence that this opal is actually dyed hydrophane from Ethiopia’s Wollo Province. The fine untreated Wollo opals on the cover consist of a 35.32 ct oval cabochon in the center courtesy of William Larson (Palagems.com, Fallbrook, California) surrounded by two pieces of rough (8.16 and 12.78 g) and four polished stones (6.95–32.55 ct) that are courtesy of David Artinian (Clear Cut Inc., Poway, California). Photos by Robert Weldon. Color separations for Gems & Gemology are by Pacific Plus, Carlsbad, California. Printing is by Allen Press, Lawrence, Kansas. GIA World Headquarters The Robert Mouawad Campus 5345 Armada Drive Carlsbad, CA 92008 USA © 2011 Gemological Institute of America All rights reserved. ISSN 0016-626X GREAT EXPECTATIONS e all have great expectations for 2012. I’ve gone a step further with my New Year’s resolutions by creating a “goals” book. W Not only do I write down my goals, but I also add details such as how and when I will achieve them, and include pictures to make it more visual. So, what new things can you expect from Gems & Gemology in the year ahead? Our goal is to create an enhanced digital journal, one that offers a more interactive experience for our online audience, in support of what we already do. Digital is changing the way information is consumed, and it pro- vides a unique opportunity to reinvent the way we engage with you, our readers. Digital is beyond relevant: It is the future. But first we finish 2011. Our final issue of the year includes a report by GIA researchers on a new purple opal that’s been hitting the market. Although it was reportedly natural material from Mexico, gemological investigation identified it as dyed opal from Ethiopia. Because this hydro- phane opal can be very absorbent, Our goal is to create an enhanced digital journal, one we can expect to see many other that offers a more interactive experience for our online treatments applied to it. audience, in support of what we already do. Another piece by GIA researchers examines symmetry parameters in diamond grading. Thanks to improve- ments in measuring round brilliants with optical scanners, GIA can now evaluate symmetry more consistently. This measurement-based procedure will complement the visual assessment of symmetry, which is one of the components of GIA’s diamond cut grade. We also feature a set of six antique brooches, apparently