Sillimanite is an alumino-sillicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist B. Silliman (1779-1824).
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Sillimanite is one of three alumino-sillicate polymorphs, the other two being andalusite and kyanite. A common variety of sillimanite is known as fibrolite, so named because the mineral appears like a bunch of fibres twisted together when viewed under thin section or even by the naked eye. Both the fibrous and traditional forms of sillimanite are common in metamorphosed sedimentary rocks.
|Colours||White, brown and green|
|Lustre||Silky if in fibrous form, else vitreous|
|Pleochroism||Colourless to pale brown to yellow|
|Type locality||Vltava, Susice, Czech Republic.|