Andalusite
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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.<ref>International Colored Gem Association: Anadalusite</ref> 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.
[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] Details
| Crystallographic system | Orthorhombic |
| Colours | Brown, green, pink, violet and red varieties |
| Lustre | |
| Hardness | 7.5 |
| Specific gravity | 3.13 - 3.17 |
| Refractive index | 1.641-1.648 |
| cleavage | 3 |
| Twinning | Lamellar |
| Pleochroism | Clear to patchy pink |
[edit] Related minerals
[edit] See also
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[edit] References
[edit] Notes
es:Andalucita eo:Andaluzito it:Andalusite lt:Andalūzitas hu:Andalúzit nl:Andalusiet pl:Andaluzyt pt:Andaluzita sv:Andalusit
