arch 1, 1999 is a watershed date in the gem and jewelry trade. This is when General Electric (GE) and Lazare Kaplan International (LKI) unveiled their latest contribution to the diamond and jewelry industry: diamonds that had undergone a new GE process "designed to improve their color, brilliance, and brightness" (Rapnet, 1999). Colloquially, these diamonds became known as "GE POL" or "Pegasus" diamonds, because they were being marketed through LKI subsidiary Pegasus Overseas Ltd. (POL). At the July 2000 Jewelers of America trade show in New York, however, the brand name Bellataire was officially launched. The first gemological description of GE POL diamonds appeared in fall 1999, when GIA published an overview of the macroscopic and microscopic features observed in 858 GE POL diamonds they had examined up to August 1999 (Moses et al., 1999). Subsequent articles by the SSEF Swiss Gemmological Institute and De Beers provided more analytical details on GE POL diamonds and suggested spectroscopic methods of identification (Chalain et al., 1999, 2000; Fisher and Spits, 2000). The Gübelin Gem Lab (GGL) has had an ongoing cooperation with GE, LKI, and POCL (Pegasus Overseas Company Ltd.) to investigate the gemological and analytical characteristics of GE POL diamonds, in order to help develop identification criteria. Because of this collaboration, staff members at GGL were given the opportunity to document a selection of diamonds taken from current GE production, both prior and subsequent to high pressure/high temperature (HPHT) processing (figure 1). This study represents the first independent investigation of actual GE POL diamonds both before and after processing by General Electric. Such an investigation is crucial to understanding the mechanisms behind the color alteration and thus to providing greater insight into potential methods of identification. The present report not only addresses the alterations in color, inclusions, graining, and strain produced by the GE process, but it also considerably expands the

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Abstract. Pumice from the``Minoan eruption'' on Thera (Cyclades, Greece) was investigated to reveal the differences between the composition of the bulk material, which contains a certain percentage of crystallites, and the pure glass phase. This is important for the identi®cation of vitric tephra layers found in the Eastern Mediterranean region in archaeological context and in deep sea drilling cores. Eruption products, deposited at some distance, have usually lost their crystalline fraction due to gravity separation and consist only of glass shards. Only major element distributions in such layers and in pumiceous glass phases have been published up to now, but these data are not suf®cient for a reliable identi®cation of the volcanic source, as several other eruptions are known to have produced chemically very similar layers in this region (Milos, Nisyros, Yali, Kos). Therefore, a technique has been developed to separate the glass phase from the primary pumice to reveal differences in the trace element distributions obtained by instrumental neutron activation analysis (INAA). X-ray diffractometry and microscopical techniques were applied to check the purity of this fraction. The concentrations of the major constituents, in particular Al, Ca, Fe, K, Mg, Mn, Na, Si, and Ti were determined by X-ray¯uorescence (XRF) and electron probe microanalysis (EPMA), those of Al, Ba, Ca, Ce, Co, Cr, Cs, Dy, Eu, Fe, Hf, K, La, Lu, Mn, Na, Nd, Rb, Sb, Sc, Sm, Ta, Ti, Th, U, Yb and Zr by instrumental neutron activation analysis and partly also by X-ray¯uorescence. Subtle differences between the compositions of the glass phase and the bulk material are explained by differentiation during partial crystallization and their applicability to the classi®cation of tephra layers is demonstrated.

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