536 GEOGRAPHIC ORIGIN OF BLUE SAPPHIRE GEMS & GEMOLOGY WINTER 2019 T he twentieth century witnessed a surge of dis- coveries of blue sapphire deposits around the world. As the gem trade has evolved alongside these developments, geographic origin determination has become a major consideration in buying and sell- ing sapphires. In some cases, the value of a stone can depend strongly on its origin, such as the Kashmir sapphires shown in figure 1. The trade largely relies on reputable gemological laboratories to make these origin determinations, which are based on compari- son with extensive reference collections (see Vertri- est et al., 2019, pp. 490–511 of this issue) and advanced analytical methods (see Groat et al., 2019, pp. 512–535 of this issue). After more than a decade of efforts by GIA’s field gemology and research de- partments to acquire reliable samples in the field and collect reference data, blue sapphire remains one of the greatest challenges when it comes to origin de- termination. The following sections will detail the origin data GIA has collected for blue sapphire and describe the laboratory’s methodology for using this data in geographic origin determination. SAMPLES AND ANALYTICAL METHODS The sapphires included in this study are almost exclu- sively from GIA’s reference collection, which was built over more than 10 years by GIA’s field gemology department. Stones in GIA’s reference collection were obtained by gemologists from reliable sources and col- lected as close to the mining source as possible (see Vertriest et al., 2019, pp. 490–511 of this issue). When necessary, the data from the reference collection were supplemented by stones from the personal collections of the authors of this study or from GIA’s museum col- lection. The trace element data were collected from 606 samples total for metamorphic sapphires and 342 samples total for basalt-related sapphires: 124 from Sri Lanka, 263 from Madagascar, 219 from Myanmar (for- merly Burma), 72 from Nigeria, 67 from Australia, 72 from Thailand, 46 from Cambodia, and 85 from Ethiopia. In modern times it has not been possible to collect Kashmir sapphires through the field gemology program. Therefore, data presented here for Kashmir sapphires are from observations on historic stones and collections with verifiable provenance or those that could be independently verified through multiple lines of evidence. GEOGRAPHIC ORIGIN DETERMINATION OF BLUE SAPPHIRE Aaron C. Palke, Sudarat Saeseaw, Nathan D. Renfro, Ziyin Sun, and Shane F. McClure FEATURE ARTICLES Geographic origin determination, one of the most pressing issues facing modern gemological laboratories, is especially challenging for blue sapphire. Reliable origin determination requires careful analysis of a stone’s in- clusions and trace element chemistry as well as spectroscopic data. Some stones have characteristic inclusion scenes or trace element chemistry that make it easy to determine their origin, but in many cases there is signif- icant overlap for blue sapphire from distinct geographic localities. The most commonly encountered inclusions are rutile silk and particle clouds. In some stones the silk or clouds may take on a distinct appearance and the origin may be accurately determined. But in many cases the evidence presented by inclusions within a stone is ambiguous. This contribution outlines the methods and criteria used at GIA for geographic origin determination of blue sapphire. In Brief • Geographic origin can have a significant impact on the value of fine blue sapphires. • Origin determination for metamorphic blue sapphires relies heavily on their inclusions, while there is signifi- cant overlap in their trace element chemistry. • Basalt-related blue sapphires tend to have largely over- lapping inclusions, but trace element chemistry is more useful in origin determination. See end of article for About the Authors and Acknowledgments. GEMS & GEMOLOGY , Vol. 55, No. 4, pp. 536–579, http://dx.doi.org/10.5741/GEMS.55.4.536 © 2019 Gemological Institute of America