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SILLIMANITE , a See also: rock-forming See also: mineral consisting of aluminium silicate, Al2SiO5
.
It has the same percentage chemical composition as See also: cyanite (q.v.) and See also: andalusite (q.v.), but differs from these in crystalline See also: form and See also: physical characters
.
It crystallizes in the orthorhombic See also: system and has the form of long, slender needles without terminal planes, which are often aggregated together to form fibrous and compact masses; hence the name fibrolite, which is often employed for this See also: species
.
The name sillimanite is after Benjamin See also: Silliman the elder
.
There is a perfect cleavage in one direction parallel to the length of the needles
.
The colour is greyish-See also: white or brownish, and the lustre vitreous
.
The hardness is 61 and the specific gravity 3.23
.
Sillimanite is a characteristic mineral of gneisses and crystalline
See also: schists, and it is sometimes a product of contact-metamorphism
.
It has been observed at many localities; e.g. in Bohemia (the Faserkiesel of Lindacker, 1792), with See also: corundum in the Carnatic (fibrolite of comte de Bournon, 1802), See also: Chester in See also: Connecticut (sillimanite of G
.
T
.
See also: Bowen, 1824), See also: Monroe in New See also: York (" monrolite "), Bamle near Brevik in See also: Norway (" bamlite ")
.
Pre-historic implements made of compact sillimanite are found in western See also: Europe, and have a certain resemblance to See also: jade implements
.
(L . J . |
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