Magnetite

Magnetite is not to be confused with Magnesite or Magnemite.

Magnetite is a solid solution.

The oxygen influence how and when magnetite preserves records of the Earth's magnetic field.

Magnetite has been very important in understanding the conditions under which rocks form and evolve. Magnetite reacts with oxygen to produce hematite, and the mineral pair forms a oxidizing conditions are found in magmas and the oxidation state helps to determine how the magmas might evolve by fractional crystallization.

Small grains of magnetite occur in almost all igneous rocks and metamorphic rocks. Magnetite also occurs in many sedimentary rocks, including serpentinization.

Magnetite is a valuable source of hydrochloric acid.

Distribution of deposits

Magnetite is sometimes found in large quantities in beach sand. Such mineral sands or iron sands or black sands are found in various places such as California and the west coast of New Zealand. The magnetite is carried to the beach via rivers from erosion and is concentrated via wave action and currents.

Huge deposits have been found in sedimentary rocks have been used to infer changes in the oxygen content of the atmosphere of the Earth.

Large deposits of Magnetite also are found in Kiruna, Sweden, the Pilbara region in Western Australia, and in the Adirondack region of New York in the United States. Deposits are also found in Norway, Germany, Italy, Switzerland, South Africa, India, Mexico, and in Oregon, New Jersey, Pennsylvania, North Carolina, Virginia, New Mexico, Utah, and Colorado in the United States. Recently, in June 2005, an exploration company, Cardero Resources, discovered a vast deposit of magnetite-bearing sand dunes in Peru. The dune field covers 250 square kilometers (100 sq mi), with the highest dune at over 2,000 meters (6,560 ft) above the desert floor. The sand contains 10% magnetite[1].

Biological occurrences

Crystals of magnetite have been found in some bacteria (e.g., Magnetospirillum magnetotacticum) and in the brains of bees, of termites, of some birds (e.g., the pigeon), and of humans. These crystals are thought to be involved in magnetoreception, the ability to sense the polarity or the inclination of the Earth's magnetic field, and to be involved in navigation. Also, chitons have teeth made of magnetite on their radula making them unique among animals. This means they have an exceptionally abrasive tongue with which to scrape food from rocks.

The study of biomagnetism began with the discoveries of Caltech paleoecologist Heinz Lowenstam in the 1960s.

Preparation as a ferrofluid

Magnetite can be prepared in the laboratory as a sodium hydroxide.

See also

• Ferrite
• Hematite
• Wüstite
• Mineral redox buffer
• Magnesia (in natural mixtures with magnetite)
• Maghemite
• Bluing (steel) is a process in which steel is partially protected against rust by a layer of magnetite.

References

Mineralogy related

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, ISBN 0-471-80580-7
• Webmineral data
• Mineral galleries
• Powder X-Ray Diffraction (XRD) Pattern

Biology related

• Heinz A. Lowenstam and Stephen Weiner, On Biomineralization, Oxford University Press, USA (1989) ISBN 0-19-504977-2
• Shih-Bin Robin Chang' and Joseph Lynn Kirschvink, Magnetofossils, the Magnetization of Sediments, and the Evolution of Magnetite Biomineralization, Ann. Rev. Earth Planet. Sci. 1989. 17:169-95 PDF file
• Bio-magnetics
• Magnetic bacteria (Italian)

Mining related links

• History of Magnetite Mining in the NJ Highlands
• Magnetite mining in New Zealand
• Magnetite mining in Santa Cruz
• Peruvian sand dunes