magnetite

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magnetite (loadstone, lodestone) An important rock-forming iron oxide Fe2+Fe3+2O4 (FeO.Fe2O3) and member of the spinel group of minerals; belongs to the magnetite series along with magnesioferrite (MgFe3+2O4), franklinite, jacobsite (MnFe3+2O4), and trevorite (NiFe3+2O4); sp. gr. 5.2 (to 4.6); hardness 5.5–6.5; cubic; normally iron-black with a blue tarnish; black streak; sub-metallic lustre; crystals often octahedral and rhombdodecahedral, but it is also massive and granular; cleavage poor, octahedral; strongly magnetic; found extensively in magmatic rocks associated with basic rocks, in pegmatites, in contact metasomatic zones (especially in limestones in regionally metamorphosed rocks due to the dehydration of iron hydroxides), and also in black sands associated with gold gravels.

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magnetite (măg´nətīt), lustrous black, magnetic mineral, Fe3O4. It occurs in crystals of the cubic system, in masses, and as a loose sand. It is one of the important ores of iron (magnetic iron ore) and is a common constituent of igneous and metamorphic rocks. It is found in Norway, Sweden, the Urals, and various parts of the United States. A variety of magnetite, lodestone (or loadstone) exhibits polarity and is especially interesting for its natural magnetism; Magnet Cove, Ark., became famous as a source.

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magnetite Iron oxide mineral (Fe3O4). It is a valuable iron ore, found in igneous and metamorphic rocks. It is black, metallic and brittle. Permanently magnetized deposits are called lodestone. Hardness 6; r.d. 5.2.

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mag·net·ite / ˈmagnəˌtīt/ • n. a gray-black magnetic mineral that consists of an oxide of iron and is an important form of iron ore.