GIA Winter G&G: Graining, Pearls & Rare Gem Materials

From GIA, Carlsbad, Calif. – The Winter 2006 edition of the Gemological Institute of America’s (GIA) Gems & Gemology, which mailed Jan. 25, features articles on the effect of graining on diamond clarity grading at GIA and the identification of one type of treated “chocolate pearls.” Also appearing in this issue are reports on two unusual gem materials.

Leading the Winter issue is “The Impact of Internal Whitish and Reflective Graining on the Clarity Grading of D-to-Z Color Diamonds at the GIA Laboratory,” by John M. King, technical director at the GIA Laboratory, and co-authors. Unlike many other grading characteristics, clarity grading involving whitish and reflective graining takes into consideration a number of factors beyond examination at standard 10x magnification. Such graining can be significant because it may be the only internal feature present in large, high-color diamonds. In addition to reviewing the types and known causes of such graining, the article also describes the methodology that GIA diamond graders use to determine the impact of graining on the clarity grade of a diamond.

“The elusive nature of whitish and reflective graining in diamonds has led to confusion in the trade about how these characteristics affect clarity grades,” remarked Gems & GemologyEditor in Chief Alice S. Keller. “This is a must-read article for anyone who handles diamonds, especially top-color higher-clarity stones.”

The second article, “Identification of ‘Chocolate Pearls’ Treated by Ballerina Pearl Co.,” examines this popular new type of treated cultured pearls. With this study, Dr. Wuyi Wang and a team of GIA Laboratory colleagues set out to learn more about the origin of the treated color and determine the means by which these products could be identified. The authors conclude that the Ballerina “Chocolate Pearls” have been subjected to a bleaching process and can be identified based on their unusual coloration, characteristic fluorescence, spectroscopic features, and trace-element composition.

The Winter issue also contains two articles on little-known gem materials. In “Leopard Opal: Play-of-Color Opal in Vesicular Basalt from Zimapán, Hidalgo State, Mexico,” Robert Raymond Coenraads and Alfonso Rosas Zenil summarize the gemological properties of this unusual material, which formed as opal was deposited in porous basaltic lava flows. In “The Cause of Iridescence in Rainbow Andradite from Nara, Japan,” Thomas Hainschwang and Franck Notari study the characteristics of this attractive garnet from southern Japan. The article explains how two different types of microscopic layered structures are most likely the cause of the spectacular iridescence.

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The Lab Notes column features the latest discoveries from the GIA Laboratory, including lizards inimitation amber, an unusual pink diamond that changed from Fancy Deep pink to Fancy Deep orangy pink during testing for ultraviolet fluorescence, and a Fancy White diamond with unusual banded graining. The Gem News International section reports on the current status of diamond trading in Sierra Leone and gem mining in Mogok (Myanmar), small treated synthetic pink diamonds set in a ring, Sunset quartz from Brazil, and more.

Also included in the Winter issue is the annual index, compiling all material from 2006, and a list of the 2006 Gems & Gemology Challenge winners.

To order the new Winter 2006 issue or to subscribe, visit http://www.gia.edu/ or contact Circulation Coordinator Debbie Ortiz at dortiz@gia.edu or call toll-free 800-421-7250, ext. 7142. Outside the U.S.and Canada, call 760-603-4000, ext. 7142.