The SSEF Swiss Gemmological Institute received a number of attractive rubies with uncommon features at April's BaselWorld jewelry fair in Switzerland. The stones, which were submitted by different dealers, all had a rather saturated red hue, and their internal features indicated they were clearly unheated. The largest weighed 10.75 carats (figure 1). Qualitative chemical analysis of all the samples with energy-dispersive X-ray fluorescence spectroscopy established that Cr and Fe were the main trace elements, while Ga was low and Ti and V were below detection limits. The client was sure of the stone's Tanzanian origin and expected to see that country identified on the test report. Because SSEF had not seen faceted rubies with such characteristics before, it was not possible to specify the origin at that time.

We recalled, however, a small parcel of rough corundum from a new deposit in Tanzania that was supplied in January 2008 by Werner Spaltenstein, a buyer in East Africa. These samples were represented to him as coming from the village of Winza, which is located near Mpwapwa, about 85 kilometers east-southeast of Dodoma. A comparison of this material with the cut stones examined during the Basel fair showed a similar chemical composition, and some of the inclusions were identical. They included bent fibers that were actually hollow channels filled with a polycrystalline substance (probably secondary minerals; figure 2), and partially healed fissures consisting of idiomorphic cavities with a polycrystalline filling of white and black grains. Therefore, we concluded that the rubies seen at the fair were indeed from Winza.

The faceted gems we have seen thus far from this new deposit suggest there is considerable potential for high-quality rubies from Winza that in some cases do not need enhancement. But as with all deposits, a considerable amount of lower-quality material is probably present—in this case, as fractured stones with blue color zones. Such corundum will likely be subject to flux-assisted heat treatment to remove the blue spots and "heal" the fractures.

Henry A. Hänni
SSEF Swiss Gemmological Institute