GSA 2017 Annual Meeting

Tao Hsu, James E. Shigley, and Dona Dirlam

The Geological Society of America (GSA) held its annual meeting October 22–25 in Seattle. For the fifth year, GIA hosted technical sessions on gemological research in the 21st century. More than 30 researchers, students, and gem experts from multiple institutions shared their most recent research results (figure 1).

Invited speaker Evan Smith (GIA, New York) presented the diamond inclusion suite study he carried out over the past two years. Following his paper published in Science on type IIa Cullinan-like, large, inclusion-poor, pure, irregular, resorbed (CLIPPIR) diamonds, Dr. Smith investigated in situ mineral phases in more than 20 extremely rare type IIb diamonds selected from GIA’s day-to-day grading operations. The identified inclusions indicated that type IIb diamonds can originate from the lower mantle, at depths beyond 660 km. This surprising result refuted the well-accepted view that almost all superdeep diamonds are small and not of gem quality. Nancy McMillan (New Mexico State University) talked about the diamond provenance study she performed with Catherine McManus (Materialytics, Killeen, Texas). To ease consumer concerns about conflict diamonds, they conducted multivariate analysis of laser-induced breakdown spectroscopy (LIBS) on diamonds from various origins as well as synthetic diamonds. The information provided by LIBS on trace element composition and the electronic structure of atoms in diamonds aided in provenance determination. Through infrared (IR) mapping, Sally Eaton-Magaña (GIA, Carlsbad) and her colleague Troy Ardon documented the spatial changes of the optical defect center B⁰ (uncompensated boron) in two type IIb diamond samples: One specimen was irradiated along an edge and then annealed, while the other was only annealed. The irradiated diamond showed an obvious gradient in B⁰ across the specimen itself and larger gradient changes during annealing compared to the other sample. These were caused by changes in compensating defects, which were then plotted by photoluminescence (PL) mapping.

The following three presenters from the University of Alberta shared their intriguing diamond formation research. Mandy Krebs offered trace element data of fluids trapped in gem-quality diamonds and compared them to those in fibrous diamonds that have been extensively studied. The results showed clear similarities in trace element patterns in both categories, which indicates that fibrous diamonds and gem diamonds may share a common origin. Rebecca Stone reported on diamond growth in saline fluid. She and her colleagues carefully documented diamond growth features under different salinities using a mixed KCl-NaCl brine system within the diamond stability field. Their series of experiments showed that Na-rich brine is a better medium for diamond growth than K-rich or Na+K mixed brines. Robert Luth discussed the partial melting mechanism facilitating diamond formation. He noted that the amount of diamond formed during this process depends on the lithology being melted and the composition of the fluid. The origin of the C-bearing fluid was also explored.

Following the diamond research presentations, invited speaker Darrell Henry (Louisiana State University) started the colored stone session with a talk on gem tourmaline. He pointed out that tourmaline is a very sensitive mineral that can incorporate and retain chemical and textural fingerprints from its environment. Paraíba, Paraíba-like, liddicoatite, and “chrome” tourmaline were used to illustrate this mineral’s incredible scientific value. Aaron Palke (GIA, Carlsbad) discussed his recent findings on demantoid garnet’s coloration mechanism. The existing theory attributes the brown coloration of this gem to intervalence charge transfer between Fe²⁺ and Ti⁴⁺ or Fe³⁺. Dr. Palke challenged this interpretation based on recent spectroscopic results showing insufficient Fe²⁺ in demantoid to justify this mechanism. Philippe Belley (University of British Columbia) addressed the challenges of modeling spinel deposits. His potential solutions are based on detailed petrographic and geochemical studies on 14 samples from exceptionally well-exposed in situ spinel occurrences on Baffin Island in Nunavut, Canada. Donald Lake (University of British Columbia) compared two beryl occurrences in northern Canada with Colombian emerald deposits. He pointed out that in terms of formation environment, these potential emerald deposits are the first “Colombian-type” sources outside Colombia. Rachelle Turnier (University of Wisconsin–Madison) presented her study on oxygen isotope fractionation factors in corundum. Oxygen isotope ratios are important to understanding corundum genesis and origin determination. This study empirically calibrated the calcite-corundum oxygen isotope fractionation factor from the metamorphosed karst-bauxite deposits at Naxos, Greece. GIA’s Jennifer Stone-Sundberg closed this portion of the session with a presentation on matrix-matched corundum standards development. She explained the importance of these newly developed standards in accurately determining trace element concentration and elaborated on the advantages of these standards over other commonly used products.

This year’s poster session attracted 18 presenters, triple the number from last year (figure 2). Daniel Howell (University of Padua) presented new applications of DiaMap software in automated and semi-automated mapping of single substitutional defects (N and B) and micro-inclusion-bearing diamonds. Paul Johnson (GIA, New York) reported the first observation of nickel as the cause of the green color of an HPHT synthetic diamond. Nickel is commonly used in the metal flux that produces HPHT synthetic diamond, but it rarely contributes to diamond coloration. Tyler Sundell (Missouri State University) evaluated the viability of in situ ¹³C measurement in diamonds using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Tingting Gu (GIA, New York) shared her study on micro- and nano-inclusions containing both N and Fe in type IaB diamonds. Kyaw Soe Moe (GIA, New York) presented the identification features of irradiated and annealed pink diamonds using IR spectroscopy and DiamondView imaging. Elizabeth Levy (Louisiana State University) explained how to directly measure Fe²⁺ and Fe³⁺ concentration in tourmaline crystals using synchrotron-based X-ray absorption near-edge spectroscopy (XANES). Cole Mount (New Mexico State University) found that using multivariate analysis of LIBS spectra of tourmaline can remove the negative influence of chemical zoning on host lithology determination. Ulrika D’Haenens-Johansson (GIA, New York) gave her insights on the 812 ct Constellation and two other large rough diamonds. FTIR and morphology observations indicate that the three could possibly be pieces from the same rough. Christopher M. Breeding (GIA, Carlsbad) described the first ever co-occurrence of magnesite, olivine, graphite, and silicon-vacancy defects in natural diamonds and explored the unusual conditions under which these diamonds formed. Karen Smit (GIA, New York) discussed the formation of peridotitic diamonds through isochemical cooling and eclogitic diamonds through redox buffering. George Harlow (American Museum of Natural History, New York) and Rachelle Turnier discovered that syenite-hosted sapphires from six different sources show a wide range of δ18O values, which indicates scavenging of sapphire from multiple reservoirs. Troy Ardon (GIA, Carlsbad) used IR mapping, cathodoluminescence (CL) imaging, and hyperspectral mapping to correlate various optical and infrared point defects in diamonds with strong brown coloration. Susanne Schmidt (University of Geneva) outlined U-Pb geochronology work done on zircon inclusions in Sri Lankan sapphires. This study was performed by her former graduate student Emilie Elmaleh. Ziyin Sun (GIA, Carlsbad) investigated the role of chromophore vanadium in coloration of pyrope-spessartine garnet, using samples without a color-change phenomenon. Eric Brinza (University of Wisconsin–Eau Claire) described an IR spectroscopic study on hydrothermal quartz crystal. Different hydroxyl species concentrations vary both vertically and horizontally through the crystal. Kyle Tollefson, also of the University of Wisconsin–Eau Claire, presented IR and visible spectroscopic study on coloration of watermelon tourmaline. The results showed that the chromophore was incorporated during crystal growth and could reflect changes in the growth environment. Dona Dirlam and her coauthors from GIA’s Richard T. Liddicoat Gemological Library and Information Center (Carlsbad, California) chronicled the legendary John Sinkankas, whose collection of books and other publications was acquired by GIA in 1988 to form the basis of its world-renowned gemological library.