Characterization and Grading of Natural-Color Yellow Diamonds John M
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Summer 2005 VOLUME 41, NO. 2 EDITORIAL _____________ 87 The Experts behind G&G: Our Editorial Review Board Alice S. Keller FEATURE ARTICLES _____________ 88 Characterization and Grading of Natural-Color Yellow Diamonds John M. King, James E. Shigley, Thomas H. Gelb, Scott S. Guhin, Matthew Hall, and Wuyi Wang Using a sample base of more than 24,000, this article explores the color grading of natural-color yellow diamonds at the GIA Gem Laboratory and pg. 89 reports on their gemological and spectroscopic properties. 116 Emeralds from the Kafubu Area, Zambia J. C. (Hanco) Zwaan, Antonín V. Seifert, Stanislav Vrána, Brendan M. Laurs, Björn Anckar, William B. (Skip) Simmons, Alexander U. Falster, Wim J. Lustenhouwer, Sam Muhlmeister, John I. Koivula, and Héja Garcia-Guillerminet The geology, production, and gemological properties of emeralds from this, the second largest emerald-producing country in the world, are described. 150 Mt. Mica: A Renaissance in Maine’s Gem Tourmaline Production William B. (Skip) Simmons, Brendan M. Laurs, Alexander U. Falster, John I. Koivula, and Karen L. Webber This historic deposit is once again producing fine tourmalines, with both the mining area and the gems examined in this report. pg. 146 REGULAR FEATURES _____________________ 164 Lab Notes Two unusual fracture-filled diamonds • Large diamond with micro-inclusions of carbonates and solid CO2 • Light blue diamond with type IIb and IIa zones • Natural type Ib diamond with unusually high N content • Diamond with unusual laser drill holes • Yellowish orange magnesioaxinite • Cultured pearl with cul- tured-pearl nucleus • Dyed “golden” freshwater cultured pearls • More on Cu- bearing color-change tourmaline from Mozambique 176 Gem News International Demantoid from northern Pakistan • Pyrope-almandine from Ethiopia • New pg. 172 ruby and pink sapphire deposit in Kenya • Faceted orange and brown sunstone from India • Staurolite in kyanite from Brazil • Obsidian with spessartine inclu- sions • Fluorite inclusions in quartz from Madagascar • Bismuthinite inclusions in rose quartz from Madagascar • Yellow hydrothermal synthetic sapphires seen in India • Interesting heated citrine • “Chocolate” Tahitian cultured pearls • Lead glass–filled rubies appear in the Middle East • GemmoBasel 2005 report 189 Book Reviews 192 Gemological Abstracts 200 The Last Page: The Other Side of the Lens pg. 183 The Experts behind Gems & Gemology: Our Editorial Review Board hat sets a peer-reviewed journal apart from other publications is its editorial review board. And what makes Gems & Gemology unique as a professional journal is the intellect that our reviewers bring to the task. W Our review board members, who represent many different aspects of gemological research, independently evaluate submitted manuscripts for accuracy, research methodology, and usefulness to the journal’s readership. Every manuscript that makes it to the pages of G&G has been improved by their comments and suggestions. The members of this panel are dedicated to the advancement of gemology, working long hours with no remuneration. It is with great pride and gratitude that I take this opportunity to profile the Gems & Gemology Editorial Review Board. • Shigeru Akamatsu is a leading authority on cultured • Anthony R. Kampf conducts research in the areas of descrip- pearls. A former manager of the Pearl Research Laboratory at tive mineralogy, crystal chemistry, and structural crystallogra- K. Mikimoto & Co. and currently senior manager of its busi- phy. Dr. Kampf is curator and section head of mineral sciences ness administration department, Mr. Akamatsu is also vice- at the Natural History Museum of Los Angeles County. president of the CIBJO Pearl Commission. • Robert E. Kane is a former manager of identification at the • Alan T. Collins is an expert in the study of color centers GIA Gem Trade Laboratory and former director of the and point defects in natural, synthetic, and treated diamonds. Gübelin Gem Lab in Lucerne, Switzerland. He continues to A widely published author and frequent lecturer, Dr. Collins write on various gemological topics as president of Fine is professor of physics at King’s College London. Gems International in Helena, Montana. • G. Robert Crowningshield, a former vice president of the • Alfred A. Levinson is an authority on diamond deposits. A GIA Gem Trade Laboratory, is a legend in gemology (see former editor of Geochimica et Cosmochimica Acta, Dr. Levinson profile in the Fall 2003 G&G, pp. 184–199). Mr. Crowning- is professor emeritus of geology at the University of Calgary. shield began writing for G&G in 1949 and was the longtime • Thomas M. Moses has written a number of important editor of the Lab Notes section. research articles dealing with gem identification and the • John L. Emmett is a leading authority on laser applications characteristics of natural and synthetic diamonds. Mr. Moses and heat treatment of gem materials. Formerly associate is vice president of identification and research services at the director of the Lawrence Livermore National Laboratory, Dr. GIA Gem Laboratory in New York. Emmett is co-founder and president of Crystal Chemistry, a • George R. Rossman is professor of mineralogy at the company specializing in the heat treatment of corundum. California Institute of Technology, where he received the • Emmanuel Fritsch has written numerous research articles, 2003–2004 Richard P. Feynman Prize for Excellence in most related to the application of spectroscopy to gemology, Teaching. Among Dr. Rossman’s research interests is the study the origin of color in gem materials, and treated and synthet- of how electromagnetic radiation interacts with minerals. ic gems. Formerly with GIA Research, Dr. Fritsch is professor • Kenneth Scarratt has more than 30 years of laboratory of physics at the University of Nantes, France. experience and is one of the world’s leading authorities on • Henry A. Hänni is a prolific author and lecturer. His natural and cultured pearls. Formerly head of the AGTA research interests include advanced analytical techniques, Gemological Testing Center, Mr. Scarratt is director of the pearl formation, and corundum treatments. Dr. Hänni is new GIA research facility in Bangkok. director of the SSEF Swiss Gemmological Institute in Basel • James E. Shigley, an important contributor to G&G and and professor of gemology at the University of Basel. many other journals, is also the editor of the new volume • C. S. Hurlbut Jr. is professor emeritus of mineralogy at Gems & Gemology in Review: Synthetic Diamonds. Dr. Harvard University. A 1955 Guggenheim fellow, he has writ- Shigley has been director of GIA Research since 1986. ten several books on gemology and mineralogy. Dr. Hurlbut • Christopher P. Smith is a widely published gemologist who is a past president of the Mineralogical Society of America. has performed research on HPHT-treated diamonds, rubies • A. J. A. (Bram) Janse, a well-known expert on diamond and and sapphires, and gem treatments. Formerly head of the kimberlite occurrences, has been involved in diamond explo- Gübelin Gem Lab, Mr. Smith is director of identification ser- ration worldwide for nearly 50 years. Dr. Janse is managing vices at the GIA Gem Laboratory in New York. director of Archon Exploration Pty Ltd. in Perth, Australia. • Alan Jobbins has more than 50 years of experience as a G&G appreciates the selfless contributions of our review- gemologist. A former editor of Journal of Gemmology, he was ers. These are truly the experts behind Gems & Gemology. the longtime curator of gems and minerals at the Geological Museum in London. Mr. Jobbins is president of Gem-A, London. • Mary L. Johnson is a frequent contributor to G&G. As man- ager of research and development at GIA Research in Carlsbad, Dr. Johnson has helped lead the Institute’s groundbreaking Alice S. Keller studies on emerald fillers and diamond cut proportions. Editor-in-Chief EDITORIAL GEMS & GEMOLOGY SUMMER 2005 87 CHARACTERIZATION AND GRADING OF NATURAL-COLOR YELLOW DIAMONDS John M. King, James E. Shigley, Thomas H. Gelb, Scott S. Guhin, Matthew Hall, and Wuyi Wang To better understand the yellow diamonds currently in the marketplace, as well as identify possible changes in their trends seen over a five-year period, researchers at the GIA Gem Laboratory ana- lyzed gemological data collected on more than 24,000 natural-color yellow diamonds examined in the calendar years 1998 and 2003. These data included color grade, type of cut, clarity grade, weight, ultraviolet fluorescence, and UV-visible and infrared spectra. Among natural-color colored diamonds, those with a yellow hue are some of the most abundant; even so, they are much less common than the colorless to light yellow diamonds associated with GIA’s D-to-Z color grading scale. Since the yellow color is a continuation of the gradation of color associated with the D-to-Z scale, there can be misconceptions about the color grading, which involves different procedures from those used for D-to-Z grading. The grading and appearance aspects, as well as other charac- teristics of yellow diamonds, are discussed to clarify these differences. The authors have also identi- fied five subgroups of type I yellow diamonds, which (with some overlap) are characterized by rep- resentative spectra and color appearances. oday, yellow diamonds are among the most This article presents data on more than 24,000 widely encountered of the “fancy color” dia- fancy-color yellow diamonds that were examined T monds (figure 1). From 1998 to the present, by the GIA Gem Laboratory during the years 1998 GIA has issued grading reports on more than and 2003. While our main concern in this study was 100,000 yellow diamonds, by far the most common gathering information to characterize the gemologi- of the fancy-color diamonds submitted to our labo- cal and spectroscopic properties of the entire popu- ratory. In 2003, for example, 58% of the diamonds lation of samples, we were also interested in identi- submitted for GIA Colored Diamond Grading fying any trends in size, color grade, or clarity grade Reports or Colored Diamond Identification and among the yellow diamonds submitted to us that Origin of Color Reports were in the yellow hue.