A variety of epidote that is transparent and typically deep bluish-violet, but also sometimes of other hues. The paler stones are subjected to heat treatment to produce the blue colour desired for gemstones. Transparent stones are faceted, cloudy ones are cut en cabochon. A specimen called 'Midnight Blue', weighing 122,7 carats, is at the Natural History Museum, Washington, DC.
The stones somewhat resemble sapphire but are lighter and softer. Tanzanite was discovered in 1967 in Tanzania (the state formed in 1964 by the merging of Tanganyika and Zanzibar) through the aid of Henry B. Patt, of Tiffany & Co., and was so named by him; in 1968 it was introduced by Tiffany to the jewelry world.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson