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Andalusite

Andalusite is an alumino-silicate mineral with the chemical formula Al2SiO5.

Occurrence Andalusite is a common 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.

Details

Crystallographic systemOrthorhombic
ColoursBrown, green, pink, violet and red varieties
Lustre
Hardness7.5
Refractive index 1.641-1.648
Cleavage3
TwinningLamellar
PleochroismClear to patchy pink

Related minerals

  1. Kyanite
  2. Sillimanite
  3. Chiastolite[?]



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