cassiterite(redirected from cassiterites)
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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.
(or tinstone), a mineral with the chemical composition Sno2. Theoretically it contains 78.62 percent Sn but usually includes impurities of Nb, Ta, Zr, Sc, W, and Fe; thus, the Sn content varies within 68–78 percent.
Cassiterite crystallizes in the tetragonal system, forming prismatic or dipyrimidal crystals. Geniculated twins are characteristic. The crystalline structure is analogous to that of rutile. Cassiterite is usually encountered in the form of small and large crystals, drusoid aggregates, or compact granular masses as well as in the form of cryptocrystalline, colloform segregations, concretions, and sinter formations. The color is dark brown, almost black, yellow with a reddish brown cast; nearly colorless varieties are also known. Cassiterite has an adamantine luster, a hardness of 6–7 on the mineralogical scale, and a density of 6, 040–7, 120 kg/m3 (lowest in light-colored cassiterite).
The deposits are usually genetically linked with granitic rocks. The most interesting commercial accumulations of the mineral are characteristic for hydrothermal quartz-cassiterite and sulfide-cassiterite veins. Cassiterite is stable in zones of oxidation and surface weathering; with the destruction of primary deposits, it accumulates in placers. In the USSR, cassiterite deposits are found in the northeast in Primor’e, in Middle Asia, and in the Kazakh SSR. Abroad, it is found in Malaysia, Thailand, Indonesia, the People’s Republic of China, Bolivia, Nigeria, and elsewhere. Cassiterite is the chief ore for obtaining tin.
A. B. PAVLOVSKII