Pink Topaz from Pakistan

Abstract

In addition t o the relatively recent discovery o f significant amounts of emerald, aquamarine, and ruby, Pakistan has also begun to produce fine gem-quaii t y pink topaz. In a small hillock of recrystallized limestone north o f Katlang, narrow calcite veins encase pink topaz crystals up to 3 c m long accompanied b y larger amounts o f reddish brown, tan, and colorless topaz crystals. More than 70,000 ct of gem-quality pink topaz has been reported t o date. The refractive indices, optic axial angle, unit-cell dimensions, and density of the topaz are influenced b y a partial replacement o f fluorine b y hydroxyl ions. The color i s due to trace elements -principally chromium (Cr3+). Treatment experiments revealed that the color o f the brown, tan, and colorless topaz f rom this source m a y be improved b y irradiation and heat.