Summer 2020 G&G Available Now
October 22, 2020
The Summer 2020 edition of Gems & Gemology concludes the fancy-color diamond series with a discussion on yellow and orange diamonds and wraps up the saga of the Chivor emerald mine in Colombia. The issue also explores a surface luminescence imaging technique to separate natural from laboratory-grown diamond, the use of fluorescence spectroscopy to identify pearls that have been optically whitened and brightened, the geographic origin determination of nephrite based on isotope ratios, and more.
Naturally Colored Yellow and Orange Gem Diamonds: The Nitrogen Factor
The lead article, by Christopher M. Breeding and co-authors, investigates the four major defect groups responsible for the color in most yellow and orange diamonds. They conclude their fancy-color diamond series by focusing on yellow diamonds, the most commonly encountered colored diamonds of all, and their much rarer orange relatives.
Separation of Natural from Laboratory-Grown Diamond Using Time-Gated Luminescence Imaging
De Beers Group Technology has developed a method to easily separate colorless and near-colorless natural and synthetic diamond using an expansion of the surface luminescence imaging employed by the DiamondView. Colin D. McGuinness and co-authors explain how blue delayed luminescence can be used as an identifier for more than 99% of natural type IIa and type Ia diamond. This improved imaging technique helps eliminate the need for time-consuming and expensive testing.
History of the Chivor Emerald Mine, Part II (1924-1970): Between Insolvency and Viability
Karl Schmetzer and co-authors bring a dramatic close to the Chivor emerald mine’s rich history with part two. This story resumes after the controlling company, the Colombian Emerald Syndicate, Ltd., succumbed to bankruptcy in 1923. The tale continues with countless twists and turns involving stock market speculation, insolvency, and ownership changes.
Optical Whitening and Brightening of Pearls: A Fluorescence Spectroscopy Study
Cultured pearls often undergo a bleaching process and maeshori treatment to improve their appearance. However, the pearl trade also employs chemical compounds known as optical brightening agents to enhance the appearance of these goods. Chunhui Zhou and co-authors explore the use of fluorescence spectroscopy to quickly and effectively separate optically brightened pearls from those that are untreated or have undergone routine bleaching.
Hydrogen and Oxygen Stable Isotope Ratios of Dolomite-Related Nephrite: Relevance for Its Geographic Origin and Geological Significance
Hydrogen and oxygen stable isotope ratios can be used to distinguish the four most important origins of dolomite-related nephrite. Kong Gao and co-authors compare ratio values in samples from Russia, South Korea, and two locations in China and discuss how these ratios are related to ore-forming fluids. Combined with unique gemological characteristics such as color, luster, and transparency from specific nephrite deposits, these isotope ratios can be used to determine geographic origin.
GIA laboratory staff present their latest findings in the Lab Notes section, including quench-crackled dyed blue chalcedony resembling Larimar, an exceptional purple sapphire from Montana, and HPHT-processed CVD laboratory-grown diamonds with low color grades.
The Micro-World section, dedicated to the inner world of gemstones, features unusually shaped rutile crystal inclusions in Russian emerald, windmill inclusions in the rare mineral sphalerite, and crystalline pyrite inside a 466.27 ct rock crystal quartz.
Gem News International
Finally, GNI correspondents from around the world report on a possible new find of purplish pink diaspore, the impact of ivory bans on the fossil ivory trade, the design and cutting of the “Fragility of the Eternal” kunzite, “rhodatrolite” from Indonesia, and a field trip to Crater of Diamonds State Park in Arkansas.
Brooke Goedert is associate editor of Gems & Gemology at GIA in Carlsbad, California.