Zoisite is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. Its chemical formula is Ca2Al3(SiO4)(Si2O7)O(OH). Zoisite is named after the Slovene scientist Baron Sigmund Zois von Edelstein (Žiga Zois), who realized that this was an unknown mineral when it was brought to him by the mineral dealer Simon Prešern, who had discovered it in the Saualpe mountains (Svinška planina) of Carinthia in 1805. Zoisite was first known as saualpite, after its type locality.
Zoisite occurs as prismatic, orthorhombic (2/m 2/m 2/m) crystals or in massive form, being found in metamorphic and pegmatitic rock. Zoisite may be blue to violet, green, brown, pink, yellow, gray, or colorless. It has a vitreous luster and a conchoidal to uneven fracture. When euhedral, zoisite crystals are striated parallel to the principal axis (c-axis). Also parallel to the principal axis is one direction of perfect cleavage. Zoisite is somewhat higher than 6 in hardness and its specific gravity is between 3.10 - 3.38, depending on the variety. Zoisite streaks white and is said to be brittle. Clinozoisite is a more common monoclinic polymorph of zoisite.
Sources of zoisite include Tanzania (tanzanite), Kenya (anyolite), Norway (thulite), Switzerland, Austria, India, Pakistan, and Washington in the USA.
1. ^ http://rruff.geo.arizona.edu/doclib/hom/zoisite.pdf Handbook of Mineralogy
* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
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