Smithsonite

Smithsonite, also known as zinc spar, is the mineral form of zinc carbonate (ZnCO₃). 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 scientist James Smithson (c. 1765–1829), who first identified the mineral in 1802.^[3][5]

Smithsonite
General
Category	Carbonate mineral
Formula	ZnCO3
IMA symbol	Smt[1]
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	[2][3][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.^[4] A bright yellow variety is sometimes called "turkey fat ore". The cause of the yellow colour is due to the presence of greenockite inclusions within the smithsonite crystals.^[2]

Gallery

• 
  Botryoidal smithsonite: Ojuela Mine, Mapimi, Mun. de Mapimi, Durango, Mexico
• 
  Botryoidal smithsonite mass from the Lavrion District Mines, Greece
• 
  Crystals of pink cobaltoan smithsonite on matrix
• 
  Apple-green cuprian smithsonite crystals. A second generation of drusy smithsonite was deposited in the crevasses between the larger growth.
• 
  Crystals of slightly pink cobaltoan smithsonite, Tsumeb, 6.8 × 4.6 × 3.7 cm
• 
  Blue smithsonite from the Kelly Mine in New Mexico

See also

• List of minerals
• List of minerals named after people