Gem stories: Tanzanite

Fine Tanzanite eye clean heart, weighing 7.28 cts from Tanzania

Tanzanite is the trade name given by the gemmologists at Tiffany & Co to the transparent violet-blue variety of Zoisite, the mineral which was described by Abraham Gottlob Werner in 1805. Tanzanite is generally enhanced by heat unless otherwise specified. The unheated crystals can be green, violet, yellowish or, light blue but a brownish root beer color is most common. Heating at 380 degrees C will produce the intense top blue sapphire color. Surprisingly, it is the dark brown crystals that produce the most valuable dark blue stones after heating. The treatment is permanent and accepted in the trade.