Formula:{Ca₂}{Al₃}(Si₂O₇)(SiO₄)O(OH)

Species: Silicates – (Sorosilicate)

Colour: A gem variety of zoisite with a blue to blue-violet colour. The colour is due to the incorporation of trace amounts of vanadium cations. Zoisite can be colourless, purple, greyish-white, grey, yellowish-brown, yellow, pink, green. Tanzanite crystals have distinct pleochroism, that is crystals show different colors depending on the viewing direction. Thus the faceters must orient the stone carefully for the best color. 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.

Lustre: Vitreous, Pearly

Hardness: 6 – 7

Specific Gravity: 3.15 – 3.36

Crystal System: Orthorhombic

Name: Zoisite was originally named saualpite for the locality Saualpe in Carinthia, Austria, where it occurs in eclogites. The name zoisite was introduced by A.G. Werner in 1805 to honour Sigmund Zois, Baron von Edelstein (1747-1819), Austrian scholar who financed mineral-collecting expeditions. It was from Baron Zois that Werner obtained the holotype specimen from Saualpe (found by mineral dealer Simon Prešern in 1804).

Type Locality: First reported in1967 from the Merelani Hills (Mererani), Tanzania.