Feature
Gems & Gemology, Fall 1986, Vol. 22, No. 3
Pink Topaz from Pakistan
Edward Gübelin, Giorgio Graziani, and A. H. Kazmi
In addition to the relatively recent discovery of significant amounts of emerald, aquamarine, and ruby, Pakistan has also begun to produce fine gem-quality pink topaz. In a small hillock of recrystallized limestone north of Katlang, narrow calcite veins encase pink topaz crystals up to 3 cm long accompanied by larger amounts of reddish brown, tan, and colorless topaz crystals. More than 70,000 ct of gem-quality pink topaz has been reported to date. The refractive indices, optic axial angle, unit-cell dimensions, and density of the topaz are influenced by a partial replacement of fluorine by hydroxyl ions. The color is due to trace elements—principally chromium (Cr3+). Treatment experiments revealed that the color of the brown, tan, and colorless topaz from this source may be improved by irradiation and heat.
