Smithsonite

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Smithsonite
A specimen of smithsonite from Tsumeb, Namibia, in the Smithsonian Institution.
General
Category	Calcite Group Mineral
Chemical formula	ZnCO₃
Identification
Molecular Weight	125.40 g/mol
Color	white, Yellow, green, blue, purple
Crystal habit	massive to well crystaline
Crystal system	Trigonal
Twinning	None observed
Cleavage	Perfecton the [1011]
Fracture	uneven, sub-conchoidal
Tenacity	Brittle
Mohs Scale hardness	4.5
Luster	Vitreous
Ultraviolet fluorescence	None
Streak	White
Density	4.43 g/cm³
Diaphaneity	Translucent
References	^[1]^[2]

Smithsonite, or zinc spar, is zinc carbonate Zn C O₃, 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

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.

Smithsonite occurs as a secondary mineral in the weathering or oxidation zone of zinc bearing ore deposits. It sometimes occurs as 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.