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sillimanite




sillimanite
Also called fibrolite, a mineral, aluminum silicate (Al2SiO5), found in mica schists and gneiss. Its crystals are of the orthorhombic system, usually fibrous masses, and are satin-like or glossy white, brown, green, or blue. A pale blue gem variety occurs in Sri Lanka. Hardness 6–7.5; relative density 3.2.


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   • GEOLOGY AND PLANETARY SCIENCE