The name tanzanite (after the east African state of Tanzania) was introduced by the
New York Jewelers Tiffany & Co. It is accepted by the trade, although scientists
do not encourage a multitude of names for gemstones and refer to it as blue zoisite.
In good quality the color is ultramarine to sapphire blue; in artificial light, more
amethyst violet. When heated to 752-932F/400-500C the yellow and brown tints
vanish, and the blue deepens. Tanzanite cat's eyes are also found. Some deposits
in Tanzania near Arusha occur in veins or filling of fissures of gneissis.