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magnetite (Fe3O4)


magnetite
A hard, black, strongly ferromagnetic (see magnet and ferromagnetism) form of iron oxide that is one of the major ores of iron, second only to hematite. Magnetite crystallizes in the cubic system and is a mixed iron(II)-iron(III) oxide; it belongs to the spinel group of minerals. It is widely distributed and occurs as an accessory mineral in many igneous and metamorphic rocks. The largest deposits are found in northern Sweden. Magnetite was used in the ancient world as a compass, under the name lodestone.


Magnetite and life

Tiny crystals of magnetite are produced by some terrestrial bacteria, known as magnetotatic bacteria, and used for orientation. The discovery of similar crystals in some Mars meteorites, including ALH84001, has been taken as evidence of past martian life, though this claim is hotly disputed.


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