GSA Meeting – GIA Session
A session of presentations on gemological research topics, organized by GIA, took place during the recent annual meeting of the Geological Society of America (GSA) in Portland, Oregon (October 10–13, 2021). Aaron Celestian of the Natural History Museum of Los Angeles began the oral presentations with a description of a famous piece of furniture—the Borghese-Windsor Cabinet—created in Italy around 1620. The large, multi-drawer wooden cabinet was decorated with semi-precious gems, including agate and lapis lazuli. A study of the geographic origin of the agates indicated that most were from the Idar-Oberstein area of Germany, with the remainder from another source. The early construction date of the cabinet makes Brazil an unlikely source for the agate; another possibility would have been India.
Cisil Badur of the Department of Geosciences of Auburn University in Alabama reported on plagioclase sunstones from the Columbia River basalts in Oregon that exhibit a schiller effect due to oriented copper inclusions. Argon-argon geochronological data indicate that the sunstones are younger in age than the host basalt. The author suggests this age discrepancy might be due to argon loss over geological time from the feldspar crystals, or it could be explained by the host basalt having been formed during a younger period of regional volcanism. A second talk on copper in Oregon sunstones was given by Shiyun Jin of GIA (figure 1). Rapid diffusion of copper in labradorite feldspars can induce red or green colors and aventurescence depending on the size of the exsolved copper particles. These tiny particles produce a red color by selective absorption of incident light or, in larger specimens, a green color by scattering red and orange light.
Rhiana Henry of the Department of Earth, Ocean and Atmospheric Sciences of the University of British Columbia investigated the sodium and water contents of the main varieties of beryl to develop a method to calculate water contents in beryl based on the more easily measured sodium contents. Rachelle Turnier of the Geoscience Department of the University of Wisconsin in Madison investigated oxygen isotope contents of sapphire from a variety of primary and secondary sources in Montana. She found a wide range of δ18O values in the corundum samples. This large range suggests that the Montana sapphire deposits originated from corundum formation in a variety of protolith source rocks. Aaron Palke of GIA studied what was initially thought might represent a rare new group of sapphire from the Rock Creek deposit in Montana. Although displaying a crystal shape and inclusions typical of sapphires from this area, these new sapphires exhibited low iron and gallium compositions. Dr. Palke emphasized the need for caution in using trace-element contents to decipher the geological origins of gem corundum and reported that these pale or yellow-colored sapphires do not represent a new group of material. Rather, they are typical Rock Creek sapphires that exhibit very low iron and gallium contents.
Zinc-enriched, fracture-filled, and fibrous overgrowths on classic Paraíba tourmaline crystals from Brazil were described by Darrell Henry from the Department of Geology and Geophysics at Louisiana State University in Baton Rouge. Such features are not observed in cuprian tourmalines from Nigeria or Mozambique, and thus they may be diagnostic of the original Paraíba material. Yicen Liu of the Gems and Technological Material Laboratory of Tongji University in Shanghai detailed the color mechanism and effects of heat treatment on spectral features and color for pink spinel from the famous Kuh-i-Lal deposit in Tajikistan. Che Shen of the Munsell Color Science Laboratory at the Rochester Institute of Technology described a method to calculate the color appearance of optically uniaxial colored gemstones.
Gabriela Farfan of the Department of Mineral Sciences of the Smithsonian Institution in Washington, DC discussed the effect of environmental factors on freshwater pearl mineralogy and chemistry. In a study of a lake in Kentucky, the pearl samples recorded oxygen isotope ratios and crystallographic signatures that could be correlated with seasonal variations in lake temperature, dissolved oxygen, and light levels at a one-meter depth. Chunhui Zhou of GIA reported the discovery of disordered dolomite crystals in the central internal structure of a natural pearl from a Cassius species mollusk.
Matthew Hardman of GIA discussed the use of multidimensional statistical analysis of the peak intensities of certain visible and near-infrared spectral features of irradiated green diamonds with and without green radiation stains. This type of spectral analysis offers a new approach to understanding the lattice defects in diamonds that result from natural and artificial radiation exposure. Roy Bassoo of GIA reported on a study of deuterium-hydrogen ratios in the low water content of nominally anhydrous minerals (such as olivine, enstatite, and garnet) found as inclusions in diamonds from the Guiana Shield in South America. This isotopic information could provide evidence for the geological conditions of diamond formation and growth in the upper mantle. Ira Litvak-Kochavi of the Department of Chemical Sciences at Ariel University in Israel discussed the results of a study of the influence on paramagnetic defect centers in diamond at the high temperatures (900°C or higher) that occur during facet polishing.
In addition to the talks, GIA staff members prepared several poster presentations for the session. Jennifer Stone-Sundberg reviewed a quantitative description of the causes of color in corundum in terms of six major chromophore elements. Stephanie Persaud described five diamonds that exhibited a temporary color change from gray to yellow or blue when subjected to extremely low, liquid-nitrogen temperatures. Wasura Soonthorntantikul discussed the spectroscopic characteristics of both unheated and heat-treated blue spinels (figure 2). Heating tended to produce a less desirable grayish blue color. Paul Johnson reported on several light blue to purple type Ia diamonds that owe their color to a lattice defect associated with artificial irradiation. Dona Mary Dirlam presented a map that showed localities in Central Asia, Southeast Asia, Africa, and Sri Lanka (as well as Europe and the Americas) that were the sources of colored stones and pearls used for jewelry purposes in India during the seventeenth century (figure 3). Troy Ardon reviewed the different spectral features found in type I and type II pink diamonds. Evan Smith discussed the discovery of metallic inclusions with a heavy iron isotopic composition in high-quality type IIa colorless diamonds. This composition is attributed to the subduction of iron minerals formed by serpentinization of oceanic peridotite. Yusuke Katsurada described a study of iron and copper absorptions in the spectrum of blue/green Paraíba tourmalines and a method to determine whether a particular elbaite would correctly be classified as a cuprian tourmaline.
Overall, the 2021 GSA annual meeting saw strong attendance and notable interest in the gemology sessions and exhibits (figures 4 and 5). The 2022 event is scheduled for October 9–12 in Denver.
