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Tanzanite Ca₂Al₃(SiO₄)₃(OH) is the blue and violet variety of the mineral zoisite, caused by small amounts of vanadium. Tanzanite belongs to the epidote mineral group. Tanzanite is only found in Tanzania, in a very small mining area near the Mererani Hills. It has a hardness of 6-6.5 on the Mohs Scale and forms according to an orthorhombic crystal system

Please note: A significant percentage of tanzanite crystals on the market have been heat-treated (400-500°C) to produce or enhance this colour, many are originally brown or pale grey (Hurlbut 1969; see photo to the right). A red tint seen looking down the c-axis is a good indication that the crystal colouration is natural.