Smithsonite, or zinc spar, is zinc carbonate ZnCO3, a mineral ore of zinc. Historically, smithsonite was identified with hemimorphite before it was realised that they were two distinct minerals. The two minerals are very similar in appearance and the term calamine has been used for both, leading to some confusion. The distinct mineral Smithsonite was first described in 1832 and named for British chemist and mineralogist, James Smithson (1754-1829), whose estate financed the Smithsonian Institution.

Smithsonite is a variably colored trigonal mineral which only rarely is found in well formed crystals. The typical habit is as earthy botryoidal masses. It has a Mohs hardness of 4.5 and a specific gravity of 4.4 to 4.5.

SmithsoniteSmithsonite occurs as a secondary mineral in the weathering or oxidation zone of zinc bearing ore deposits. It sometimes occurs a replacement bodies in carbonate rocks and as such may constitute zinc ore. It commonly occurs in association with hemimorphite, willemite, hydrozincite, cerussite, malachite, azurite, aurichalcite and anglesite. Forms two limited solid solution series, with substitution of manganese leading to rhodochrosite and with iron leading to siderite.

Zinc carbonate is used in calamine lotion to treat skin diseases and reduce the itching of insect bites.