Smithsonite

Smithsonite
General
Category Carbonate mineral
Formula
(repeating unit)		 ZnCO3
Strunz classification 5.AB.05
Crystal system Trigonal
Crystal class Hexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space group R3c
Unit cell a = 4.6526(7)
c = 15.0257(22) [Å]; Z = 6
Identification
Color White, grey, yellow, green to apple-green, blue, pink, purple, bluish grey, and brown
Crystal habit Uncommon as crystals, typically botryoidal, reniform, spherulitic; stalactitic, earthy, compact massive
Twinning None observed
Cleavage Perfect on [1011]
Fracture Uneven, sub-conchoidal
Tenacity Brittle
Mohs scale hardness 4.5
Luster Vitreous, may be pearly
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 named in 1832 by François Sulpice Beudant in honor of English chemist and mineralogist James Smithson (c.1765–1829), whose bequest established the Smithsonian Institution and who first identified the mineral in 1802.[2][4]

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]

See also

Bibliography

References

  1. ↑ Smithsonite: Smithsonite mineral information and data from Mindat
  2. 1 2 Smithsonite mineral data from Webmineral
  3. 1 2 Handbook of mineralogy
  4. ↑ "Smithsonite at the National Museum of Natural History". Smithsonian Institution. Retrieved 8 December 2010.
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