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Brown, pale green, or white glassy silicate mineral that often occurs in long, slender, needlelike crystals frequently found in fibrous aggregates. An aluminum silicate, AlOSiO, 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.
Variants of SILLIMANITE
sillimanite or fibrolite
This entry comes from Encyclopædia Britannica Concise. For the full entry on sillimanite, visit Britannica.com.