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Yellow zoisite crystal (1.7 x 1 x 0.8 cm)
Category Sorosilicate - epidote group
(repeating unit)
Strunz classification 9.BG.10
Dana classification 58.2.1b.1
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnma
Color White, gray, greenish brown, greenish gray, pink, blue, purple
Crystal habit Prismatic crystals with striations; massive to columnar
Cleavage Perfect {010} imperfect {100}
Fracture Uneven to conchoidal
Mohs scale hardness 6 to 7
Luster Vitreous, pearly on cleavage surfaces
Streak White or colorless
Diaphaneity Transparent to translucent
Specific gravity 3.10–3.36
Optical properties biaxial positive
Refractive index nα = 1.696 - 1.700 nβ = 1.696 - 1.702 nγ = 1.702 - 1.718
Birefringence 0.006-0.018
Pleochroism X = pale pink to red-violet; Y = nearly colorless to bright pink or deep blue; Z = pale yellow to yellow-green
References [1][2][3]
Major varieties
Tanzanite Gem-quality zoisite, blue-purple
Thulite Pink

Zoisite, first known as saualpite, after its type locality, is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. Its chemical formula is Ca2Al3(SiO4)(Si2O7)O(OH).

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. The mineral is between 6 and 7 on the Mohs hardness scale, and its specific gravity ranges from 3.10 to 3.38, depending on the variety. It streaks white and is said to be brittle. Clinozoisite is a more common monoclinic polymorph of Ca2Al3(SiO4)(Si2O7)O(OH). Transparent material is fashioned into gemstones while translucent-to-opaque material is usually carved.

The mineral was described by Abraham Gottlob Werner in 1805. He named it after the Carniolan naturalist Sigmund Zois, who sent him its specimens from Saualpe in Carinthia.[4] Zois realized that this was an unknown mineral when it was brought to him by a mineral dealer, presumed to be Simon Prešern, in 1797.[5]

Sources of zoisite include Tanzania (tanzanite), Kenya (anyolite), Norway (thulite), Switzerland, Austria, India, Pakistan, and the U.S. state of Washington.

See also[edit]


  1. ^ http://rruff.geo.arizona.edu/doclib/hom/zoisite.pdf Handbook of Mineralogy
  2. ^ http://www.mindat.org/min-4430.html Mindat
  3. ^ http://webmineral.com/data/Zoisite.shtml Webmineral data
  4. ^ Flint-Rogers, Austin (1937). Introduction to the Study of Minerals. McGraw-Hill Book Company. p. 478. 
  5. ^ Faninger, Ernest (1988–1989). "Neue Daten über die Entdeckung des Zoisits" [New Data About the Discovery of Zoisite]. Geologija: razprave in poročila (in German and Slovenian). Državna založba Slovenije [State Publishing House of Slovenia]. 31, 32: 609–615. ISSN 0016-7789. 


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