GSA 2015 Annual Meeting
The Geological Society of America’s annual meeting, held in Baltimore November 1–4, attracted more than 6,000 geoscientists from around the world. Two technical sessions, one oral and one poster, were devoted to the gemological field. The poster session’s flexible presentation time and format, along with the wide range of topics covered (including diamond defect formation and low-pressure, high-temperature [LPHT] treatment of type Ia diamonds), allowed for dynamic discussion between exhibitors and viewers.
George Harlow (American Museum of Natural History, New York) opened the oral session by discussing how gemological studies provide insight into the geological developments of Earth. Wuyi Wang (GIA) presented the discovery and distribution of [Si-V]– defects in HPHT synthetic diamonds. This study challenged the widely accepted theory that [Si-V]– defects only occur in CVD synthetic diamonds, while also showcasing photoluminescence mapping as a powerful research technique.
Laurent E. Cartier (Swiss Gemmological Institute, Basel) applied DNA analysis to the origin determination of organic gems, and this presentation focused on pearls. For the first time, gemologists can conclusively identify the mollusk species of a pearl; Dr. Cartier’s team is exploring similar possibilities with coral and ivory.
Karen Smit (GIA) studied the Re-Os isotope of sulfide inclusions in type Ib diamond from West Africa. The isotopic study was used to explain the assembly of the Gondwana supercontinent. Steven Shirey (Carnegie Institution of Washington) presented his Re-Os geochronology study on a sulfide inclusion within a superdeep diamond from Brazil. The age of this inclusion indicated crystal recycling facilitated by mental convection beneath. Both studies demonstrated the vital role gem materials play in earth science research.
Gemological studies of famous stones and historical jewelry pieces were also represented. Alan Hart (Natural History Museum, London) studied the creation of the Mogul cut. Using the Koh-i-Noor diamond as a case study, Mr. Hart found that differential hardness was the key factor that brought about the Mogul cut with the primitive cutting tools available in the mid-19th century. Raquel Alonso-Perez (Harvard University) used both spectroscopic and trace-element analysis to study the tourmalines mounted in the Hamlin Necklace, a piece of 19th-century North American jewelry.
Inclusion study is one of the pillars of modern gemology. John Koivula (GIA) pointed out the possibility of misidentifying synthetic corundum as heat-treated natural material. Experimental studies have demonstrated that heat-fused cracks generated in both pulled and flame-fusion synthetic corundum appear virtually identical to the features associated with so-called flux-healed natural stones. Aaron Palke, also of GIA, hypothesized that unusual glassy melt inclusions found in sapphires from southwestern Montana are crystallized as peritectic minerals formed during high-grade metamorphism, generating silica-rich melt and an alumina-rich restite. Future research on this topic may shed light on the source and transportation of Montana sapphires.
Phenomenal gems were also explored. Keal Byrne (Smithsonian Institution) investigated the luminescence of “chameleon” diamonds, which show an intriguing color-change response to temperature and/or light. Xiayang Lin (Pennsylvania State University) discovered the microscopic surface feature that causes iridescence in natural quartz crystals from India.
Researchers also spoke about American gem deposits. Michael Wise (Smithsonian Institution) discussed his work on the hydrothermal emerald and hiddenite mined in the Hiddenite area of North Carolina, while Yury I. Klyukin (Virginia Polytechnic Institute and State University) investigated the fluid evolution of the emerald deposit at the North American Emerald Mine, also in the Hiddenite region. William B. “Skip” Simmons (Maine Mineral and Gem Museum) shared the recent discovery of gem-quality pollucite in Mt. Mica pegmatite.
The details of all oral presentations from the GSA meeting can be found at https://gsa.confex.
com/gsa/2015AM/webprogram/Session37638.html. GSA’s 2016 annual meeting will be held September 25–26 in Denver.