corundum, spinel, Tajikistan.12, balas ruby, gems

Large spinel from Tajikistan. Spinel is another gem material being recovered from this former Soviet republic in Central Asia. We know of one particularly exceptional stone, a 532-ct piece of rough spinel, that was fashioned into a number of gems. The largest of these gems weighed 146.43ct and was named the Katherina" by the purchaser of the rough, the Netherlands-based ACT International (see "Spectacular Spinel," by P. Bancroft, Lapidary loiunal, February 1990, p. 25). The Katherina was subsequently recut to 123.14ct (E. Caplan, pers. comm., 1995) and the refashioned stone loaned to GIA for examination. Although recut, it retained its basic step-cut cushion shape (figure 16).The stone exhibited properties consistent with natural spinel from other localities. Described as "virtually flawless" in the Lapidary lournal article, the stone revealed a small plane of what appeared to be octahedral negative crystals near the culet when examined with magnification. These substantiate the stone's natural origin. EDXRF chemical analysis by GIA Research showed only a tiny amount of zinc (Zn), which is consistent with Zn concentrations that have been documented in other spinels from this locality."