A few months ago, the West Coast laboratory was asked to identify the attractive green oval mixed cut shown in the figure. This 12 ct item was remarkably well cut and showed fairly high dispersion. At first glance, it reminded us of the intense yellowish green tsavorite garnets that are mined in East Africa. Standard gemological tests (R.I. = 1.74, singly refractive; weak anomalous birefringence; and S.G. = 3.66, determined hydrostatically) seemed to verify our initial assumption. In addition, the sample did not show any inclusions. All these properties strongly suggested that it was indeed the tsavorite variety of grossular garnet.

However, when viewed with a handheld spectroscope, the sample showed a general absorption around 500 nm, which is not usually seen in tsavorite garnet. It was inert to long-wave ultraviolet radiation, but it fluoresced strong chalky yellow to short-wave UV. This reaction proved that it was not a garnet (garnets are inert to both long- and short-wave UV). Indeed, strong chalky fluorescence to short-wave UV radiation is often a characteristic of manufactured products such as glass. Additional testing was needed.

Senior research associate Sam Muhlmeister performed Raman spectroscopy and EDXRF chemical analysis to further characterize this material. The peaks obtained on the Raman matched those for glass. EDXRF revealed silicon and zirconium as major elements and the following trace elements: zinc, strontium, and the rare-earth elements yttrium and lanthanum. The rare-earth elements were undoubtedly responsible for the green coloration. While we have seen many glass imitations of popular gemstones, such high-property glass is seldom encountered in the laboratory.