Superb Smithsonite Crystals
Superb Smithsonite Crystals . Credit: Anton Watzl

WOW!!! What a superb Kelly mine smithsonite featuring incredible colour and shape! A mineral ore of zinc. Historically, smithsonite was identified with hemimorphite before it was realized that they were two different minerals. The two minerals are very similar in appearance and the term calamine has been used for both, leading to some confusion.

Smithsonite belongs to the calcite mineral group. It also forms a series as the zinc-dominant (Zn) end member with iron-dominant (Fe) siderite.

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.

Formula: ZnCO3
System: Trigonal
Colour: White, grey, yellow, ...
Lustre: Vitreous, Pearly
Hardness: 4 - 4½

The specimen in the photo is from:  Kelly Mine, Magdalena District, Socorro Co., New Mexico, USA
The Kelly Mine in Socorro County, New Mexico, USA produces celebrated blue and blue-green material of fine color in massive crusts.