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Formula:   Ca2Al3Si3O12(OH)   mineral photo

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Crystal:   Orthorhombic  
Hardness:   6  
Spec. Gr.:   N/A  
Streak:   N/A  
Cleavage:   Perfect  
Location:   Arusha,

Tanzanite is the blue to violet gem variety of the mineral zoisite. Tanzanite is found only in Tanzania, from which it was named, and zoisite was named for the Czechoslovakian Baron Zois von Edelstein. Tanzanite can be faceted into wonderful gemstones, some of which weigh up to 220 carats and are flawless. Tanzanite crystals are prismatic and heavily striated. When found, its color is frequently lavender. When heated to 620 C. the original color may alter to a rich violet blue, or a deep blue resembling sapphire. Tanzanite is fairly soft so must be worn carefully. Recently the Merelani mine (the largest producer) experienced a massive cave-in, which killed scores of miners. If and when mining resumes, tanzanite could be in short supply.

Bibliography: Bancroft, Peter, Gem and Crystal Treasures, 1984, pp. 303-306.

University of California, Santa Barbara—Department of Earth Science
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