Smithsonite is a gemstone quality zinc carbonate, sometimes referred to as "zinc spar".

Smithsonite | ‪#‎Geology

System: Trigonal
Colour: White, grey, yellow, ...
Lustre: Vitreous, Pearly
Hardness: 4 - 4½
From Tsumeb Mine, Tsumeb, Otjikoto, Namibia 

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. It forms two limited solid solution series, with substitution of manganese leading to rhodochrosite, and with iron, leading to siderite.
 
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