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Chemical Formula: Al₂SiO₅
Mineral Name: Sillimanite
Color: White to brown
Hardness: 6-7
Specific Gravity: 3.23

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Sillimanite or fibrolite is a brown, gray, white, or pale green mineral. It is a metamorphic mineral, typically found in schists and gneisses produced by regional metamorphism. Sillimanite is found in the regions of North America, Worcester, Massachusetts and Norwich. Sillimanite is an industrial mineral used in the manufacture of refactories and high temperature crucibles. It forms a orthorhombic crystal, and often shows rare distinct prismatic crystals.

Sillimanite is used in the manufacturing of mullite refactory ceramics, spark plugs, and high temperature crucibles. The chatoyant, green and blue varieties are used in jewelry, as gemstone and for ornamental carvings.