sillimanite
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mineral / chemical formula |
properties / significance / occurrence |
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sillimanite Al2SiO5 |
images - click to enlarge - top, sillimanite crystal; bottom, sillimanite crystals in biotite gneiss.
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Metamorphic white, brown or green aluminosilicate, nesosilicate polymorph of the orthorhombic system. The other aluminosilicate polymorphs are andalusite and kyanite. Sillimanite (crystal or fibrolite varieties) is an index metamorphic mineral resulting from high grade metamorphism (temperatures greater than 550 ºC and all pressures). Fibrolite, named for its characteristic microscopic appearance of bundles of fibers, is the commonest variety of sillimanite. Sillimanite is often associated with garnets, biotite, feldspars, quartz, kyanite and andalusite. |
| links: images: crystals: sillimanite, embedded; rocks: sillimanite, sillimanite2, sillimanite from Stakholmen, sillimanite from Kölaberget, in gneiss de Kerhornou, 2 ; formations: métatexite à sillimanite, Port Navalo; Série métapélitique de l'Agly, Micaschiste à sillimanite, sillimanite; thin-sections: fibrolite, 2, 3, 4, 5, 6, 7, sillimanite in biotite-garnet-cordierite schist, ppl, sillimanite in biotite-muscovite-andalusite schist, ppl, sillimanite, 2, 3, 4, 5, 6, sillimanites, biotite-sillimanite schist, b, webpages: sillimanite, Metamorphic rocks in thin section; structure: sillimanite, sillimanite and aluminosilicates for comparison andalusite, kyanite, topaz (crystals); other: Stone axes, petrographic analysis and prehistoric exchange | ||
