Gems & Gemology

Fall 2016 G&G: CVD Synthetic Diamonds Survey, Reversible Color Change in Blue Zircon

Jennifer-Lynn Archuleta
November 7, 2016
Fall 2016 Gems & Gemology Cover
Nathan Renfro’s article in this issue describes how exposing blue zircon to long-wave UV radiation causes them to turn brown, and how this color modification can be reversed. The 7.95 ct blue zircon ring on the cover is set in 18K white gold and surrounded by 2.43 carats of rubies. It is shown alongside a similar ring with a 5.46 ct tanzanite center stone. Both were designed by Loretta Castoro of Los Angeles for her KissMe collection. Photo by Kevin Schumacher, courtesy of Loretta Castoro.

CVD-grown diamonds, colored stones, and Indonesian cultured pearls are featured in the latest Gems & Gemology. The Fall 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.

Near-colorless and pink CVD-grown diamonds.
The lead article of the Fall 2016 issue reviews the characteristics reported from several hundred CVD synthetic diamonds examined by GIA over the past 13 years. These near-colorless and Fancy Vivid purplish pink samples are representative of most of the CVD-grown samples seen at GIA labs. Photo by Robert Weldon/GIA.

REVERSIBLE COLOR 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 color could be restored by exposure to incandescent light. Spectroscopic analyses pinpointed the features responsible for the color modification.

Blue zircons turned brown after LWUV exposure.
The 11 faceted blue zircons of unknown origin seen on the left all showed a brown face-up color after several minutes of long-wave UV exposure. Photo by C.D. Mengason.

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 gemological properties of the cabochon-grade material.

Sutara cabochon sapphire in pendant.
This silver pendant contains a 65.5 ct sapphire cabochon from Sutara, in the Russian
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 coauthors examined samples from the new source, recording its gemological properties, collecting chemical composition data, and discussing the material’s market potential.

Faceted Grandidierite
This 0.11 ct round brilliant grandidierite from Madagascar has no eye-visible flaws. Photo by Delphine Bruyere.

PERIDOT FROM THE CENTRAL HIGHLANDS OF VIETNAM

Recognizing 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 gemological characteristics and geochemical data of peridot from the Central Highlands to specimens from other known localities.

Peridot from Bien Ho deposit set in ring.
The light yellowish green 5.09 ct peridot in this gold ring is from Vietnam’s Bien Ho deposit. Photo by Nguyen Thi Minh Thuyet.

BEAD-CULTURED AND NON-BEAD-CULTURED PEARLS FROM LOMBOK, INDONESIA

In this field report, Nicholas Sturman and his coauthors 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 mollusks for further study and future identification purposes.

Cultured pearls from the Lombok farm.
A group of bead-cultured pearls of various hues recovered from hatchery-bred Pinctada maxima oysters at Lombok, Indonesia. Photo by Julie Poli.

LAB NOTES

Highlights from the Fall 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 colored 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 Fall 2016 GNI section provides updates on Tanzanian colored gemstone deposits, “Punsiri”-type spectral features in natural yellow sapphire, and use of the DiamondView instrument to identify impregnated jadeite.

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