Gems & gemmology

Photoluminescence Review and Gem Material from Unusual Locales in the Spring 2016 G&G


Gems & Gemology Spring 2016 Cover
This issue features G&G’s coverage of the 2016 Tucson gem and mineral shows. The cover photo shows Brian Cook’s Wheel of Light numinous pendant, which received first place in the AGTA Spectrum Awards’ Fashion Forward category. To create the pendant, Mr Cook drilled a channel into the apex of an 825 ct quartz disk and inserted rough crystals of Paraíba tourmaline, haüyne, ruby and spessartine garnet. The colours of these crystals are seen as concentric rings. A 24K gold setting, braided leather straps, a rutilated quartz length adjuster and fire agate beads complete the piece. Photo by Robert Weldon/GIA, courtesy of Brian Cook (Nature’s Geometry).

The Spring 2016 issue of Gems & Gemology explains the relevance of photoluminescence to the diamond trade and reports on Australian chrysoberyl, emerging production of Italian serpentine and Tajik variscite, the treatment processes used to create “pistachio” cultured pearls, and the recent Tucson gem shows.

An Introduction to Photoluminescence Spectroscopy for Diamond and Its Applications in Gemmology

The lead article in this issue, by GIA’s Christopher M. Breeding and Sally Eaton-Magaña, reviews the physics and methodology of photoluminescence. This analytical technique is increasingly important in the separation of treated and synthetic diamonds from natural material, and the authors explain how it helps ensure proper disclosure of growth processes and treatments within the trade.

Photoluminescence in diamond
Diamonds can show a wide range of hues and fluorescence colours. GIA regularly uses photoluminescence spectroscopy to confirm the natural origin of such diamonds. Photoluminescence is a sensitive technique that allows one to characterise the atomic-level lattice defects that act as a fingerprint of the growth and possible treatment history of diamonds; this method is based on principles that are similar to those of observed fluorescence. Photos of a portion of the Aurora Butterfly of Peace by Robert Weldon.

Chrysoberyl Recovered with Sapphires Related to Tertiary Volcanics in the New England Placer Deposits, New South Wales, Australia

German researcher Karl Schmetzer and his co-authors investigate chrysoberyl crystals from the sapphire placer deposits of Australia’s New England gem fields. Using various chemical and mineralogical properties to divide the materials into four specific subgroups, the authors explore various aspects of the material, including its unique sectorial colour zoning, pleochroism and chatoyancy.

Cabochon cut Australian chrysoberyl
While some of the chrysoberyl research samples from the sapphire placer deposits in the New England area were faceted, others were cut as cabochons, showing chatoyancy. The cat’s-eye cabochons range from 1.34 ct (6.5 × 5.9 mm) to 0.64 ct (5.1 × 4.7 mm). Photo by K. Schmetzer.

Gem-Quality Serpentine from Val Malenco, Central Alps, Italy

A team of researchers, led by Ilaria Adamo of the Italian Gemmological Institute in Milan, examines serpentine obtained from Pizzo Tremogge  a source located in the Central Alps of Italy. Spectroscopy and chemical analysis confirm the main phases of the serpentine group. In particular, the presence of antigorite indicates metamorphism at high temperatures, providing insight into the geological and petrological history of the Val Malenco region.

Identification of “Pistachio” Coloured Pearls Treated by Ballerina Pearl Co

Chunhui Zhou and his GIA colleagues perform a number of experiments on cultured pearls from P. margaritifera treated by Ballerina Pearl Co. to mimic the pistachio hue that naturally occurs in some specimens. The authors look for indicators to separate naturally coloured from treated material and to eliminate bleaching as a possible treatment process.

Pistachio pearls in oyster shell
Eight natural-colour pistachio pearls ranging from 9.70 × 9.40 mm to 15.00 × 12.30 mm, produced by black-lipped pearl oysters, were examined in this study. Photo by Sood Oil (Judy) Chia.

Variscite from Central Tajikistan: Preliminary Results

Researchers led by Andrey Litvinenko (Russian State Geological Prospecting University, Moscow) investigate the production of cabochon-grade variscite from a relatively unknown deposit in Tajikistan. While further study is required, initial results reveal the presence of relatively high levels of arsenic and sulphur that may link this source to an inactive antimony deposit located nearby.

Lab Notes

Lab Notes in the Spring issue include a report on the largest blue HPHT synthetic diamond examined in a GIA lab, an unusual emerald/emerald doublet submitted to the Tokyo lab, and the first mounted CVD synthetic melee diamond identified by GIA.

Micro-World

Micro-World continues to reveal the inner mysteries of gemstones through photomicrography. The section features pieces on svanbergite inclusions in dolomite from British Columbia, orange platelets creating iridescence in scapolite, and visible phase changes in a Sri Lankan sapphire.

Gem News International

G&G’s annual coverage of the Tucson gem shows, featuring fine coloured stones from around the world, kicks off this issue’s Gem News International section. Other entries cover colourless HPHT synthetic diamonds weighing to up 3.5 ct from China, polymer-treated hessonite, and a new sapphire rush near Vohitany, Madagascar.

Bicolour Tourmaline Pin
This 31.34 ct bicolour tourmaline pin, which contains gemstones exclusively from the Stewart Lithia mine in San Diego County, has an emotional connotation for the artist. Photo by Robert Weldon/GIA; courtesy of Paula Crevoshay.

Also in this issue the winners of the Dr Edward J. Gübelin Most Valuable Article Award are announced, along with the 2016 Gems & Gemology Challenge quiz. Response cards and online entries for the Challenge must be submitted by Friday, 5 August 2016.

Jennifer-Lynn Archuleta is the editor of Gems & Gemology.