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Andalusite
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Andalusite
Dark, rod-like andalusite crystals in a light green cordierite schist matrix (writing pen shows size).
General
Category mineral
Chemical formula Al2SiO5[1]
Identification
Color transparent to opaque brownish or yellowish green to orangy brown;[1] may be pure green,[1] brown,[1] pink,[1] violet (rare),[1] and red
Crystal system orthorhombic[1]
Twinning lamellar
Cleavage distinct in one direction[1]
Fracture uneven to conchoidal[1]
Mohs Scale hardness 7 - 7.5[1]
Luster vitreous[1]
Polish luster vitreous[1]
Refractive index 1.634 - 1.643 (+/-.005)[1]
Optical Properties double refractive, biaxial negative; chiastolite has anomalous aggregate reaction.[1] Can also display chatoyancy.
Birefringence .007 - .013[1]
Dispersion .016[1]
Pleochroism Strong. Brownish to yellowish green and brownish orange to brownish red
Ultraviolet fluorescence inert in long wave, inert to moderate green to yellowish green in short wave[1]
Specific gravity 3.17 (+/- .04)
Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5.
The variety chiastolite commonly contains dark inclusions of carbon or clay which form an X or a cross in section.
A clear variety first found in Andalusia, Spain can be cut into an interesting gemstone.[2] Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of iridescence, although the colors are actually the result of unusually strong pleochroism.
Contents
[hide]
* 1 Occurrence
* 2 Related minerals
* 3 See also
* 4 References
* 5 Notes
[edit] Occurrence
Andalusite is a common regional metamorphic mineral which forms under high pressure and/or temperature. The minerals kyanite and sillimanite are polymorphs of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to help identify the pressure-temperature paths of the host rock in which they are found.
It was first reported from Andalucia, Spain in 1789.
[edit] Related minerals
* Kyanite
* Sillimanite
* Chiastolite
[edit] See also
Wikimedia Commons has media related to:
Andalusite
* List of minerals
[edit] References
* Mineral galleries
* Webmineral
* Mindat w/ locations
* http://www.gemstone.org/gem-by-gem/english/andalusite.html
[edit] Notes
1. ^ a b c d e f g h i j k l m n o p q Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
2. ^ International Colored Gem Association: Anadalusite
This article about a specific mineral, mineraloid, or rock type is a stub. You can help Wikipedia by expanding it.
Retrieved from "http://en.wikipedia.org/wiki/Andalusite"
Categories: Aluminium minerals | Nesosilicates | Mineral stubs
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