description Sillimanite Overview
Sillimanite is an aluminium silicate mineral with the chemical formula Al2SiO5, and one of three polymorphs that also include andalusite and kyanite. It forms mainly in metamorphic rocks exposed to high temperatures and is also known as fibrolite when it occurs in fibrous aggregates. Transparent or strongly coloured material can be cut as a gemstone, with gem-quality examples reported from Sri Lanka, Myanmar, and Tanzania.
help Sillimanite FAQ
What is the chemical formula of sillimanite?
Sillimanite has the chemical formula Al2SiO5. It is an aluminium silicate mineral.
How is sillimanite related to kyanite and andalusite?
Sillimanite, kyanite, and andalusite are three polymorphs, meaning they share the same chemical formula but have different crystal structures. Their stability depends strongly on pressure and temperature.
Where does sillimanite form?
It forms mainly in metamorphic rocks exposed to high temperatures. It is commonly associated with high-grade metamorphism of aluminium-rich sediments.
What is fibrolite?
Fibrolite is the name commonly used when sillimanite occurs as a fibrous aggregate. Gem-quality sillimanite can also be cut, but fibrolite usually describes its fibrous texture rather than a separate mineral.
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