sillimanite

/sil"euh meuh nuyt'/, n.

a mineral, aluminum silicate, Al₂SiO₅, occurring in the form of long, slender, and often fibrous crystals. Also called fibrolite.

[1825-30; named after B. SILLIMAN; see -ITE¹]

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or fibrolite

Brown, pale green, or white glassy silicate mineral that often occurs in long, slender, needlelike crystals frequently found in fibrous aggregates.

An aluminum silicate, Al₂OSiO₄, it occurs in high-temperature regionally metamorphosed clay-rich rocks (e.g., schists and gneisses). Sillimanite is found at many localities in France, Madagascar, and the eastern U.S.; a pale sapphire-blue gem variety occurs in the gravels of Sri Lanka.

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▪ mineral

also called  Fibrolite,  

      brown, pale green, or white glassy silicate mineral that often occurs in long, slender, needlelike crystals frequently found in fibrous aggregates. An aluminum silicate, Al₂OSiO₄, it occurs in high-temperature regionally metamorphosed clay-rich rocks (e.g., schists and gneisses). Sillimanite is found at many points in France, Madagascar, and the eastern United States; a pale sapphire-blue gem variety occurs in the gravels of Sri Lanka. For detailed physical properties, see silicate mineral (table). Sillimanite is polymorphous (having the same chemistry but different crystal structure) with kyanite and andalusite.

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