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chalybite(kăl`ĭbīt), a mineral, varying in color from brown, green, or gray to black and occurring in nature in massive and crystalline form. A carbonate of iron, FeCO3, it serves as an iron ore, especially in the British Isles. It is widely distributed, being found also in the United States, Europe, South America, and Australia.
(also spathic iron, chalybite), a mineral, a carbonate of iron with the composition Fe[CO3]. Siderite contains 62.01 percent FeO and 37.99 percent CO2. Its composition often includes isomorphic admixtures of Mn and Mg, which replace iron; more rarely, Ca is present, as are Co and Zn. Siderite cystallizes in the trigonal system, forming rhombohedral, tabular, prismatic, or scalenohedral crystals; the last occur rarely. The mineral usually occurs as granular aggregates, sinters, concretions, spherulites, and earthy agglomerates; it forms deposits in the form of veins, strata, and irregularly shaped bodies. Siderite is yellowish white, gray or greenish gray and turns brown upon weathering. It has a hardness of 4.5 on Mohs’ scale and a density of 3,960 kg/m3.
Depending on the conditions of formation, siderite is classified as being of hydrothermal, sedimentary (infiltration and precipitation), or metamorphosed origin. During weathering and oxidation, siderite is usually converted into hydrogoethite or hydrohematite. Siderite is one of the most important minerals in iron ore.
any of the iron class of meteorites, according to modern classification. Formerly, the designation “siderite” was applied to iron meteorites that consist almost wholly of nickel-iron.