Smithsonite

Smithsonite, or zinc spar, is zinc carbonate (ZnCO3), 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. 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
General
CategoryCarbonate mineral
Formula
(repeating unit)
ZnCO3
Strunz classification5.AB.05
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupR3c
Unit cella = 4.6526(7)
c = 15.0257(22) [Å]; Z = 6
Identification
ColorWhite, grey, yellow, green to apple-green, blue, pink, purple, bluish grey, and brown
Crystal habitUncommon as crystals, typically botryoidal, reniform, spherulitic; stalactitic, earthy, compact massive
TwinningNone observed
CleavagePerfect on [1011]
FractureUneven, sub-conchoidal
TenacityBrittle
Mohs scale hardness4.5
LusterVitreous, may be pearly
StreakWhite
DiaphaneityTranslucent
Specific gravity4.4 - 4.5
Optical propertiesUniaxial (-)
Refractive indexnω = 1.842 - 1.850 nε = 1.619 - 1.623
Birefringenceδ = 0.223 - 0.227
Ultraviolet fluorescenceMay fluoresce pale green or pale blue under UV
References[1][2][3]

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

  • Tom Hughes, Suzanne Liebetrau, and Gloria Staebler, eds. (2010). Smithsonite: Think Zinc! Denver, CO: Lithographie ISBN 978-0-9790998-6-1.
  • Ewing, Heather (2007). The Lost World of James Smithson: Science, Revolution, and the Birth of the Smithsonian. London and New York: Bloomsbury ISBN 978-1-59691-029-4

References

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