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(named after the British chemist and mineralogist J. Smithson, 1765-1829), a mineral of the natural carbonate group; chemical composition, ZnCO3 (ZnO, 64.9 percent; CO2, 35.1 percent). It contains as admixtures Fe, Mn, Cd, Co, Mg, and Pb. Smithsonite crystallizes in the trigonal system. The crystals, which occur rarely, are rhombohedral or scalenohe-dral. Smithsonite usually occurs as granular or earthy masses and stalactitic aggregates with a conchoidal structure. It is, among other colors, white, yellowish, gray, or brown. Its hardness on Mohs scale is 4–4.5, and its density is 4,300–4,400 kg/m3.
Smithsonite is a typical commercial mineral from the zone of oxidation of deposits of primary zinc sulfides in limestones that is formed as a result of the replacement of the limestones. Deposits are found in northern Mexico, Greece (Laurium), Poland (Olkusz), and southwestern Africa (Tsumeb). In the USSR, there are deposits in the Kazakh SSR, Uzbek SSR, and Transbaikalia. [23–1830–]