Smithsonite
A specimen of smithsonite from Tsumeb, Namibia, in the Smithsonian Institution.
General
Category	Carbonate Mineral
Chemical formula	ZnCO3
Identification
Color	White, yellow, green, blue, purple
Crystal habit	Massive, botryoidal to reniform
Crystal system	Trigonal
Twinning	None observed
Cleavage	Perfect on [1011]
Fracture	Uneven, sub-conchoidal
Tenacity	Brittle
Mohs scale hardness	4.5
Luster	Vitreous
Streak	White
Diaphaneity	Translucent
Specific gravity	4.4 - 4.5
Optical properties	Uniaxial (-)
Refractive index	nω = 1.842 - 1.850 nε = 1.619 - 1.623
Birefringence	δ = 0.223 - 0.227
Ultraviolet fluorescence	May fluoresce pale green or pale blue under UV
References	[1][2][3]

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 English chemist and mineralogist, James Smithson (1754-1829), whose estate financed the Smithsonian Institution.^[2]

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.^[3]

[edit] Uses

Zinc carbonate is used as an astringent and excipient in shampoo. It is also used as a fireproofing filler for rubber and plastics, as a feed additive, as a pigment, in cosmetics and lotions, and in the manufacturing of porcelain, pottery, and rubber.^[4]

[edit] See also

• List of minerals
• List of minerals named after people

[edit] References

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