What is "siderite"

Siderite \Sid"er*ite\, n. [L. sideritis loadstone, Gr. ????, ????, of iron, from ???? iron.]

1. (Min.)

   1. Carbonate of iron, an important ore of iron occuring generally in cleavable masses, but also in rhombohedral crystals. It is of a light yellowish brown color. Called also sparry iron, spathic iron.

   2. A meteorite consisting solely of metallic iron.

   3. An indigo-blue variety of quartz.

   4. Formerly, magnetic iron ore, or loadstone.

2. (Bot.) Any plant of the genus Sideritis; ironwort.

n. 1 (context uncountable mineral English) a widespread brown mineral, FeCO₃, having the structure of calcite 2 (context countable English) an iron meteorite 3 An indigo-blue variety of quartz. 4 (context obsolete English) magnetic iron ore; lodestone

1. n. iron ore in the form of ferrous carbonate [syn: chalybite]

2. a meteorite consisting principally of nickel and iron

Siderite is a mineral composed of iron(II) carbonate (FeCO). 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.

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, which can encase three-dimensionally preserved fossils. 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. 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.