smithsonite

Smithsonite from Masua, Sardinia; top specimen has been cut and polished; the bottom two are botryoidal masses

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smithsonite, zinc carbonate (ZnCO₃), a mineral that was the principal source of zinc until the 1880s, when it was replaced by sphalerite. It is ordinarily found in the oxidized zone of ore deposits as a secondary mineral or alteration product of primary zinc minerals. Notable deposits are at Laurium, Greece; Bytom and Tarnowskie Góry, Pol.; Sardinia, Italy; and Leadville, Colo., U.S. For detailed physical properties, see carbonate mineral (table).