Siderite

Siderite is also the name of a type of iron meteorite.

Siderite
Siderite from Brasil
General
Category	Carbonate mineral
Chemical formula	FeCO3
Strunz classification	05.AB.05
Dana classification	14.01.01.03
Identification
Color	Pale yellow to tannish, grey, brown, green, red, black and sometimes nearly colorless
Crystal habit	Tabular crystals, often curved - botryoidal to massive
Crystal system	Trigonal - Hexagonal scalenohedral (3 2/m)
Twinning	Lamellar uncommon on{0112}
Cleavage	Perfect on {0111}
Fracture	Uneven to conchoidal
Tenacity	Brittle
Mohs scale hardness	3.75 - 4.25
Luster	Vitreous, may be silky to pearly
Streak	White
Diaphaneity	Translucent to subtranslucent
Specific gravity	3.96
Optical properties	Uniaxial (-)
Refractive index	nω = 1.875 nε = 1.633
Birefringence	δ = 0.242
Dispersion	Strong
References	[1][2][3]

Siderite is a mineral composed of iron carbonate FeCO₃. It takes its name from the Greek word σίδηρος sideros, “iron”. It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Both magnesium and manganese commonly substitute for the iron.

Siderite has Mohs hardness of 3.75-4.25, a specific gravity of 3.96, a white streak and a vitreous lustre or pearly luster.

Its crystals belong to the hexagonal system, and are rhombohedral in shape, typically with curved and striated faces. It also occurs in masses. Color ranges from yellow to dark brown or black, the latter being due to the presence of manganese (sometimes called manganosiderite).

Siderite is commonly found in hydrothermal veins, and is associated with barite, fluorite, galena, and others. It is also a common diagenetic mineral in shales and sandstones, where it sometimes forms concretions. In sedimentary rocks, siderite commonly forms at shallow burial depths and its elemental composition is often related to the depositional environment of the enclosing sediments.^[4] In addition, a number of recent studies have used the oxygen isotopic composition of sphaerosiderite (a type associated with soils) as a proxy for the isotopic composition of meteoric water shortly after deposition.^[5]

• 

  Siderite crystals with galena and quartz (size: 6.2 x 4.1 x 3.6 cm)

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  Cut siderite from Minas Gerais, Brazil (size : 5 x 3.2 mm)

References

1. ^ http://rruff.geo.arizona.edu/doclib/hom/siderite.pdf Handbook of Mineralogy
2. ^ http://www.mindat.org/min-3647.html Mindat
3. ^ http://www.webmineral.com/data/Siderite.shtml Webmineral data
4. ^ *Mozley, P.S., 1989, Relation between depositional environment and the elemental composition of early diagenetic siderite: Geology, v. 17, p. 704- 706
5. ^ *Ludvigson, G.A., Gonzalez, L.A. Metzger, R.A., Witzke, B.J., Brenner, R.L., Murillo, A.P.and White, T.S., 1998, Meteoric sphaerosiderite lines and their use for paleohydrology and paleoclimatology: Geology, v. 26, p. 1039-1042

• The Complete Book of Science, American Education Publishing, Columbus, Ohio 2005