Gems & Gemology 1995. The Katherina Red Spinel 123 cts
(Extract from Gems & Gemology magazine, fall 1995, XXXI volume)
"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 146.43 ct and was named the "Katherina" by the purchaser of the rough, the Netherlands-based AGT International (see "Spectacular Spinel" by P. Bancroft, Lapidary Journal, February 1990, p.25).
Figure 16. This 123.14ct spinel was cut from a 532ct piece of rough that came from Tajikistan’s Pamir Mountains. Courtesy of Evan Caplan, Los Angels; photo by Shane F. McClure.
The Katherina was subsequently recut to 123.14 ct (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 Journal 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."