Zoisite

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Zoisite
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General
Category Mineral
Chemical formula calcium aluminium hydroxy silicate (Ca2(Al.OH)Al2(SiO4)3
Identification
Colour Gray, yellow, blue, green.
Crystal habit Crystals flattened in an acicular manner, may be fibrously curved
Crystal system Orthorhombic
Cleavage Perfect
Fracture Uneven
Mohs Scale hardness 6.5
Luster Vitreous
Refractive index 1.69-1.70
Biref:0.007-0.010 (biaxial positive)
Pleochroism Present, dichroism or trichroism depending on colour.
Streak White or colorless
Specific gravity 3.10-3.38
Fusibility ?
Solubility ?
Major varieties
tanzanite Gem-quality zoisite, blue-purple
thulite Pink
anyolite Often found intergrown with ruby
chrome zoisite Green, uncommon

Zoisite is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. Zoisite is named after Austrian scientist Baron Sigmund Zois von Edelstein (Baron von Zois), whom discovered the mineral in the Sau-Alp mountains of Austria in 1805. Zoisite was first known as saualpite, after its type locality. Transparent material is fashioned into gemstones while translucent-to-opaque material is usually carved into sculptural works.

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 colourless. It has a vitreous luster and a conchoidal to ueven 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 the USA.

See also

Reference and external links

  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0471805807
  • Mineral Galleries (http://mineral.galleries.com/minerals/silicate/zoisite/zoisite.htm)
  • Webmineral.com (http://webmineral.com/data/Zoisite.shtml)
  • Mindat.org (http://www.mindat.org/min-4430.html)
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