andalusite
andalusite (chiastolite) A member of the Al2SiO5 (or Al2O3.SiO2) group of polymorphic minerals; the other members of this group are kyanite and sillimanite. The mineral mullite (3Al2O3.2SiO2) is related to this group of minerals; sp. gr. 3.2; hardness 6.5–7.5; orthorhombic; pink or red, sometimes grey-brown and green, transparent varieties used as gemstones; vitreous lustre; crystals prismatic with a pseudo-tetragonal form which has a characteristic cross-section, can also be massive; cleavage at right angles, distinct {110}; occurs principally in thermally metamorphosed rocks that show alteration to aggregates of white mica, in low-grade, regionally metamorphosed rocks, and also in granites and pegmatites together with corundum, tourmaline, topaz, and other minerals. The name is derived from Andalusia in Spain.
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Serpentine , serpentine A group of minerals belonging to the 1:1 group of phyllosilicates (sheet silicates) with the composition Mg6 [Si4O10](OH)8 and including t… Cancrinites , haüyne A feldspathoid and member of the sodalite group of minerals, formula (Na,Ca)4–8(Al6Si6O24)(SO4,S)1–2; sp. gr. 2.5; hardness 5.5; greyish-white… Greenstone , greenstone A low-grade, regional metamorphic rock containing actinolite, epidote, and albite, and lacking a cleavage. Greenstones form by metamorphis… Corundum , corundum Mineral, Al2O3; sp. gr. 3.9–4.1; hardness 9; trigonal; the two main varieties blue and green, but can be yellow, or brown to almost black, a… Apatite , apatite A widely distributed phosphate mineral, with the formula Ca5(PO4)3(F,Cl,OH); sp. gr. 3.1–3.3; hardness 5; hexagonal; usually a shade of green… Rock , rock1 / räk/ • n. 1. the solid mineral material forming part of the surface of the earth and other similar planets, exposed on the surface or underly…
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andalusite