Photoluminescence Review and Gem Material from Unusual Locales in the Spring 2016 G&G
April 26, 2016
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.
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.
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.
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 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 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.
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.