Autumn 2016 G&G: CVD Synthetic Diamonds Survey, Reversible Colour Change in Blue Zircon
October 31, 2016
CVD-grown diamonds, coloured stones and Indonesian cultured pearls are featured in the latest Gems & Gemology. The Autumn 2016 issue reviews the characteristics of several hundred CVD synthetic diamonds; describes how long-wave UV radiation can turn blue zircon brown; and examines the properties of Vietnamese peridot, grandidierite from Madagascar and Russian alluvial sapphire. The issue also includes a field report from a trip to a cultured pearl farm on the Indonesian island of Lombok.
OBSERVATIONS ON CVD-GROWN SYNTHETIC DIAMONDS: A REVIEW
Since 2003, GIA has examined hundreds of gem-quality CVD synthetic diamonds. As growth technology becomes more advanced, the size and quality of these synthetics continue to increase. In the lead article, Sally Eaton-Magaña and James Shigley survey several hundred CVD samples, interpreting grading factors and analytical data to gain greater insight into indicators of CVD origin.
REVERSIBLE COLOUR MODIFICATION OF BLUE ZIRCON BY LONG-WAVE ULTRAVIOLET RADIATION
After learning from gem dealers that blue zircons had turned brown after exposure to long-wave UV radiation, Nathan Renfro undertook a study to see if the blue colour could be restored by exposure to incandescent light. Spectroscopic analyses pinpointed the features responsible for the colour modification.
SAPPHIRES FROM THE SUTARA PLACER IN THE RUSSIAN FAR EAST
With only one placer deposit of gem-quality sapphire, Russia has long relied on sapphire from other parts of the world. But the Sutara River region of Russia’s Jewish Autonomous District is another potential source of corundum. A team of researchers led by Svetlana Buravleva uncovered sapphire at the deposit and studied the chemical composition and gemmological properties of the cabochon-grade material.
Far East. Photo by Svetlana Buravleva, courtesy of A. Kurnosov.
A NEW DEPOSIT OF GEM-QUALITY GRANDIDIERITE IN MADAGASCAR
A deposit of grandidierite outside Tranomaro, Madagascar, has yielded bluish green to greenish blue crystals that are among the purest known examples of this material. Delphine Bruyère and her co-authors examined samples from the new source, recording its gemmological properties, collecting chemical composition data, and discussing the material’s market potential.
PERIDOT FROM THE CENTRAL HIGHLANDS OF VIETNAM
Recognising the importance of Vietnamese peridot to the global gem industry, Nguyen Thi Minh Thuyet and colleagues established the geological and P-T formation of the material, concluding that it derives from a spinel lherzolite source. They also compared the gemmological characteristics and geochemical data of peridot from the Central Highlands to specimens from other known localities.
BEAD-CULTURED AND NON-BEAD-CULTURED PEARLS FROM LOMBOK, INDONESIA
In this field report, Nicholas Sturman and his co-authors recount their visit to a pearl hatchery in Lombok, Indonesia. There they observed the daily activities of a pearl farm and collected bead-cultured and non-bead-cultured pearls from P. maxima molluscs for further study and future identification purposes.
LAB NOTES
Highlights from the Autumn Lab Notes section include reports on the capabilities of GIA’s melee sorting service, a sapphire rough filled with green lead glass, a treated pink diamond coloured by red luminescence, and a purple fluorite inclusion in emerald.
MICRO-WORLD
G&G’s photomicrography section includes entries on unusual growth zoning in Pakistani aquamarine, etch features in spinel from Madagascar, and a mobile fluorite inclusion within quartz.
GEM NEWS INTERNATIONAL
The Autumn 2016 GNI section provides updates on Tanzanian coloured gemstone deposits, “Punsiri”-type spectral features in natural yellow sapphire, and use of the DiamondView instrument to identify impregnated jadeite.
Jennifer-Lynn Archuleta is the editor of Gems & Gemology.
