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cassiterite (tinstone) Mineral, SnO2; sp. gr. 6.8–7.1; hardness 6–7; tetragonal; usually reddish-brown to nearly black, but it can be yellowish and ruby; white to grey streak; adamantine lustre; crystals often pyramidal and prismatic, may also be massive and granular; cleavage prismatic {100}, {110}; occurs typically in high-temperature hydrothermal veins, with granites and pegmatites; associated minerals: topaz, quartz, tourmaline, mica, chlorite, and high-temperature metallic ores; also world-wide in alluvial deposits because of its resistance to chemical and physical attack. Cassiterite is the only important ore for tin.

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cassiterite (kəsĬt´ərīt), heavy, brown-to-black mineral, tin oxide, SnO2, crystallizing in the tetragonal system. It is found as short prismatic crystals and as irregular masses, usually in veins and replacement deposits associated with granites. Since it is hard, heavy, and resistant to weathering, it often concentrates in alluvial deposits derived from cassiterite-bearing rocks. It is the principal ore of tin and is mined in many countries; the most important sources are Malaysia, Thailand, China, Indonesia, Bolivia, and Russia. Except for Bolivia, nearly all of this production is from alluvial deposits.