Spring 2018 G&G: Color Origin of Green Diamonds, Iridescence in Hematite, and the Outlook from Tucson
May 11, 2018
Green is among the rarest hues found in colored diamonds, and there have been few published studies. The lead article of the Spring 2018 Gems & Gemology reviews the characteristics of these uncommon gems as observed at GIA’s labs. Other articles explore the causes of iridescence in Brazilian hematite and the application of DNA techniques to identifying Japanese akoya cultured pearls. The issue also includes coverage of the annual Tucson gem shows, the 2018 Challenge, and the results of the Dr. Edward J. Gübelin Most Valuable Article Award.
NATURAL-COLOR GREEN DIAMONDS: A BEAUTIFUL CONUNDRUM
Diamonds with natural color comprise less than 0.4% of all diamonds submitted to GIA. Of these, stones with a pure green hue are among the rarest. In the last decade, GIA labs have examined more than 50,000 natural-color green diamonds. The lead article, by Christopher M. Breeding, Sally Eaton-Magaña, and James E. Shigley, documents their properties and discusses the radiation exposure and atomic-level defects that cause this hue in diamonds, as well as the difficulties of separating natural-color and treated material.
IRIDESCENCE IN METAMORPHIC “RAINBOW” HEMATITE
Rainbow hematite was first uncovered from Minas Gerais, Brazil, and since then it has been used in award-winning jewelry pieces. Xiayang Lin and her coauthors investigate the cause of iridescence in this material through electron microscopy, atomic force microscopy, and synchrotron X-ray diffraction analysis. They assert that the iridescence arises from a periodic microstructure, consisting of spindle-shaped hematite nanocrystals containing minor Al and P impurities, resulting from arrested crystal growth.
DNA TECHNIQUES APPLIED TO THE IDENTIFICATION OF JAPANESE PINCTADA FUCATA PEARLS
One of the challenges of modern pearl identification is the separation of saltwater mollusk species that produce white, cream, or silver nacreous pearls. A team led by Kazuko Saruwatari used DNA techniques on akoya pearl-producing mollusks from Uwajima, Ehime Prefecture, Japan, to see if the mollusk species could be pinpointed. The authors were able to amplify the 16S rRNA gene from the mantle tissues of donor and host pearl oysters as well as from tiny amounts of pearl powder, and successfully identified the Pinctada fucata species.
In this issue, reports from GIA’s labs include an HPHT-processed diamond fraudulently represented as untreated, the analysis of five CVD synthetic diamonds greater than three carats, and a natural blister resulting from the entombment of a pearlfish within a P. maxima shell.
GEM NEWS INTERNATIONAL
In addition to our annual Tucson report, GNI features entries on aquamarine from Pakistan’s Shigar Valley, Concho pearls from Texas, and an irradiated and annealed blue type Ia diamond.
The Spring issue also contains the 2018 Gems & Gemology Challenge quiz. Score 75% or better and you’ll receive a certificate of completion (PDF file); earn a perfect score and your name will be listed in the Fall 2018 issue. Mail-in cards and online entries for the Challenge must be submitted by Friday, August 10, 2018.
Jennifer-Lynn Archuleta is the editor of Gems & Gemology.