Characterization and Grading of Natural-Color Yellow Diamonds John M
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.
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