Magnetite
Introduction
Magnetite is a iron oxide mineral that is one of the main iron ores. With the chemical formula Fe3O4, it is one of the oxides of iron. Magnetite is ferrimagnetic, which means it is attracted to a magnet. It is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism.
Properties
Magnetite differs from most other iron oxides in that it contains both divalent and trivalent iron. As a member of the spinel group, magnetite can form solid solutions with similarly structured minerals, including ulvospinel Fe2TiO4. Titaniferous magnetite is a valuable source of titanium, although it is not as significant a source as ilmenite and rutile. The crystal structure of magnetite is inverse spinel, with the oxygen anions forming a face-centered cubic lattice and the iron cations occupying interstitial sites.
Occurrence
Magnetite is a common mineral. Large deposits exist in Sweden, Norway, Germany, the Urals, and the United States. In the United States, significant amounts of high-grade ore have been developed in Minnesota on the Mesabi Range. Large deposits also occur in Western Australia. In addition to igneous rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake and marine sediments as both detrital grains and as magnetofossils.
Biological occurrences
Magnetite is a common accessory mineral in igneous rocks and is also found in metamorphic and sedimentary rocks. It is a common mineral in the Earth's crust and has even been detected on the moon. Magnetite also has important biological occurrences. Magnetotactic bacteria form chains of magnetite to orient themselves in the Earth's magnetic field. In humans, magnetite can be found in various parts of the brain and is hypothesized to play a role in navigation and memory.
Uses
Magnetite is a significant ore of iron and as such, is distinguished from other ores of iron by its tendency to attract and get attracted to magnets. Before the development of modern smelting techniques, magnetite was the primary ore of iron and was used to create iron tools. Today, the primary use of magnetite is as a raw material in the production of iron and steel. High-quality magnetite is also used in the manufacture of abrasives, fertilizers, and paints.