34th International Gemmological Conference
The 34th IGC was held in Vilnius, August 26–30. Pre- and post-conference field trips visited Lithuanian cultural heritage sites, as well as the historical amber-producing area along the Baltic seacoast. This event takes place every two years, with the 2017 conference scheduled for Windhoek, Namibia. Several oral and poster presentations of interest are summarized here. Abstracts of all presentations can be viewed on the conference website at www.igc-gemm
Amber was one of several topics presented at the conference. Albertus Bitinas (Klaipeda University, Lithuania) summarized the geologic setting of amber deposits in the southeast Baltic region. The amber originated from pine trees (Pinus succinifera) that thrived during the Paleogene period (65–23.5 million years ago), when the climate of northern Europe was humid. The subsequent flow of rivers redistributed pieces of amber in sediments in this region. Jonas Satkünas (Lithuanian Geological Survey, Vilnius) recounted efforts to document the country’s amber potential. He reported that 2,250 tons were recovered in the 19th century from the Curronian Lagoon along the Baltic seacoast. A recent survey of the lagoon revealed additional amber deposits with potential for development. Amber from Canada has never been seriously considered as a gem material, but Willow Wight (Canadian Museum of Natural History, Ottawa) discussed its importance for entomologists and botanists who have, over the past century, studied the animal and plant life from the Cretaceous period that became trapped and then preserved in the fossilized tree resin. Lore Kiefert (Gübelin Gem Lab, Lucerne, Switzerland) discussed the occurrence of natural green amber near Alem Ketema, Ethiopia. Green amber has been of gemological interest because of concerns that some material in the market is of natural or treated origin. Amber from the Hukawng Valley in northern Myanmar has been known for a millennium. Tay Thye Sun (Far East Gemmological Laboratory, Singapore) described a new amber locality in the Hti Lin township, in the central part of the country. Characterization of this new material demonstrated that it has many features similar to the Hukawng amber.
Thomas Hainschwang (Gemlab Liechtenstein) investigated 20 naturally colored, polycrystalline black diamonds of unknown origin, and one diamond from the Popigai impact crater in Siberia. The samples exhibited photoluminescence features suggesting micro-inclusions of carbon dioxide and lonsdaleite.
In the realm of synthetic diamonds, Hiroshi Kitawaki (Central Gem Laboratory, Tokyo) examined 15 type Ib yellow to brownish yellow synthetic diamonds that had been submitted for grading without disclosure. Visual features and spectroscopic evidence suggested post-growth high-temperature annealing, presumably to alter their color. The means of identifying both small HPHT and large CVD synthetic diamonds was reviewed by Joe Yuan (Taiwan Gemmological Institute, Taipei). Of particular importance for detection are anomalous birefringence (“strain”) patterns, UV fluorescence reactions, and spectroscopic features.
Gem occurrences along the coast of Greenland were discussed by Anette Juul-Nielsen (Ministry of Natural Resources, Nuuk). Small-scale mining of ruby and pink sapphire from Archean metamorphic rocks is currently underway in the Fiskenæsset area. The Greenland government is issuing licenses for both exploration and extraction of mineral resources.
Kentaro Emori (Central Gem Laboratory, Tokyo) discussed the value of three-dimensional plots of chemical composition data to support the country-of-origin determination of ruby and blue sapphire.
Emilie Elmaleh (University of Geneva) presented a study of zircon inclusions in metamorphic-related blue sapphires of sufficient size ( 150 microns) to allow age dating by the U/Pb method and quantitative chemical analysis. While potentially useful for country-of-origin determination, this method may be of more value for rough corundum samples because both techniques require that the zircon inclusion be present at the surface of the sample for analysis.
Hanco Zwaan (Netherlands Gemmological Laboratory, Leiden) investigated a suite of alluvial sapphires from deposits in Montana. Identification of mineral inclusions and geochemical analysis suggest that these sapphires originated in a metasomatic geologic environment.
Karl Schmetzer (Petershausen, Germany) investigated the origin of dual-color double stars in oriented needle-bearing corundum and quartz. The study concluded that the silvery white star is formed by light reflection and scattering, while the body-colored second star originated by the reflection and scattering of light from a layer near the base of the cabochons. The light producing the second star travels twice the distance down and up through the cabochon, undergoing selective absorption. The color of the second star is identical to the bodycolor of the host material.
Visut Pisutha-Arnond (Gem and Jewelry Institute, Bangkok) presented a heat-treatment study of sapphires to understand the role of beryllium in coloration. The researchers concluded that this trace element is made inactive by heating in a reducing environment, and that beryllium-diffusion treatment is only effective by heating under oxidizing conditions.
Walter Balmer (SSEF Swiss Gemological Institute, Basel) explored the presence of infrared bands at 3053 and 2490 wavenumbers as spectral evidence of beryllium diffusion treatment of sapphires.
Ahmadjan Abduriyim (GIA) investigated how residual pressure was distributed three-dimensionally by measuring such pressure around mineral inclusions in natural corundum from the New England sapphire field in New South Wales, Australia.
Shane McClure (GIA) described emeralds from the Belmont mine in Minas Gerais. The operation is the largest and most technologically advanced emerald mine in Brazil. He also followed a large rough emerald through the manufacturing process to create two cut stones (the largest weighing 18.17 ct) that were set in jewelry.
Gemological properties of pallasitic peridot from six different meteorites were presented by Masaki Furuya (Japan Germany Gemmological Laboratory, Kofu). Samples from the different meteorites could be distinguished from one another by inclusions, visible and infrared spectra, and trace element composition.
Roman Serov (Gemological Center, Lomonosov Moscow State University) investigated the heat treatment of green Russian demantoid garnet. Color changes were reversible and detected at heating temperatures as low as 400°C. Heating under reducing conditions was more effective in removing any brown component of demantoid color.
Andy Shen (China University of Geosciences, Wuhan) investigated nephrite jade samples from eight locations in China, using the linear discriminant analysis of trace element composition data as a criterion for determining their geographic origin.
Mining operations in the three main opal-producing areas of Australia—Lightning Ridge, Queensland, and Coober Pedy—were detailed by Karen Fox (Waterloo, Canada). She also explained the geologic conditions that favor opal formation in sedimentary environments.
Emmanuel Fritsch (University of Nantes, France) studied a yellow gem hyalite opal from Mexico with intense uranium-related, daylight-excited green luminescence. This is one of the few gem materials whose color is dominated by luminescence due to the presence of the uranyl ion.
Three gem minerals exhibiting photochromism, all showing a reversible change of color when exposed to ultraviolet radiation—hackmanite, tugtupite, and sodalite—were investigated by Claudio Milisenda (DSEF German Gem Lab, Idar-Oberstein). Within several hours to a day, the transient color reverted to the original color when the samples were exposed to daylight.