magnetite, 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.

or lodestone or magnetic iron ore

Iron oxide mineral (Fe₃O₄), the chief member of one of the series of the spinel group. Minerals in this series form black to brownish, metallic, moderately hard octahedrons and masses in igneous and metamorphic rocks and in granite pegmatites, stony meteorites, and high-temperature sulfide veins. Magnetite, as the name implies, is strongly attracted to a magnet. It is a common constituent of iron ores. Magnetite with an intrinsic magnetic field (a natural magnet) is known as lodestone.

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