Siderite

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Siderite is also the name of a type of iron meteorite.
Siderite
SideriteBresil2.jpg
Siderite from Brasil
General
Category Carbonate mineral
Formula
(repeating unit)
FeCO3
Strunz classification 05.AB.05
Dana classification 14.01.01.03
Crystal symmetry Trigonal hexagonal scalenohedral
H-M symbol: (32/m)
Space group: R 3c
Unit cell a = 4.6916 Å, c = 15.3796 Å; Z=6
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(II) 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. Zinc, magnesium and manganese commonly substitute for the iron resulting in the siderite-smithsonite, siderite-magnesite and siderite-rhodochrosite solid solution series.[2]

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.

It crystallizes in the trigonal crystal 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.

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]

References[edit]

  1. ^ Handbook of Mineralogy
  2. ^ a b Mindat
  3. ^ 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