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| − | {{Copyedited}}{{Images OK}}{{Submitted}}{{Approved}}{{Paid}}
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| − | {{Infobox mineral
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| − | | name = Magnetite
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| − | | image = Magnetite Russia.jpg
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| − | | caption = Magnetite from the [[Kola Peninsula]], [[Russia]]
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| − | | formula = [[iron(II,III) oxide]], Fe<sub>3</sub>O<sub>4</sub>
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| − | | molweight =
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| − | | color = Black, greyish
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| − | | habit = [[Octahedral]], fine granular to massive
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| − | | system = [[Cubic (crystal system)|Isometric]]
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| − | | twinning =
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| − | | cleavage = Indistinct
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| − | | fracture = Uneven
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| − | | mohs = 5.5 - 6.5
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| − | | luster = Metallic
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| − | | refractive = Opaque
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| − | | opticalprop =
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| − | | birefringence =
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| − | | pleochroism =
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| − | | streak = Black
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| − | | gravity = 5.17 - 5.18
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| − | | density =
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| − | | melt =
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| − | | diagnostic =
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| − | | solubility =
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| − | | diaphaneity =
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| − | | other =
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| − | | var1 = [[Lodestone]] | var1text = Magnetic with definite north and south poles
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| − | }}
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| − | '''Magnetite''' is a [[magnetism|ferrimagnetic]] [[mineral]] and one of several types of [[iron oxide]]. Its common chemical name is '''ferrous-ferric oxide''', its official ([[IUPAC]]) name is '''iron(II,III) oxide''', and its chemical formula is '''[[Iron|Fe]]<sub>3</sub>[[Oxygen|O]]<sub>4</sub>'''. It is a member of the [[spinel]] group of minerals and its [[crystal]]s are black and opaque. It is the most [[magnetic]] of all naturally occurring minerals on [[Earth]]. [[Lodestone]], used as an early form of magnetic [[compass]], was a naturally magnetized form of magnetite.
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| − | This mineral is a valuable [[iron]] [[ore]]. In addition, as it carries the dominant magnetic signature in rocks, it has played a critical role in understanding [[plate tectonics]]. Changes in the [[oxygen]] content of the [[Earth's atmosphere]] can be inferred by studying [[sedimentary rock]]s containing magnetite. Moreover, interactions between magnetite and other oxide minerals have been studied to determine the oxidizing conditions and evolution of [[magma]]s over geological history.
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| − | == Occurrence ==
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| − | Magnetite occurs in many [[sedimentary rocks]], and huge deposits have been found in [[banded iron formation]]s. In addition, this mineral (especially in the form of small grains) occurs in almost all [[igneous rock|igneous]] and [[metamorphic rock]]s. Many igneous rocks contain magnetite-rich and [[ilmenite]]-rich grains that precipitated together from [[magma]]. Magnetite is also produced from [[peridotite]]s and [[dunite]]s by [[serpentinite|serpentinization]].
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| − | Magnetite is sometimes found in large quantities in beach sand. It is carried to the beach by the erosive action of [[river]]s and is concentrated by waves and currents. Such [[mineral sand]]s (also called [[iron sand]]s or [[black sand]]s) are found in various places, including beaches in [[California]] and the west coast of [[New Zealand]]. In June 2005, an exploration company (Candero Resources) discovered a vast deposit of magnetite-bearing sand dunes in [[Peru]], where the highest dune is more than 2,000 meters (m) above the desert floor. The dune field covers 250 square kilometers (km²), and ten percent of the sand is magnetite.<ref>[http://www.321gold.com/editorials/moriarty/moriarty070505.html Ferrous Nonsnotus] Retrieved September 12, 2007.</ref>
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| − | Large deposits of magnetite have been found in [[Kiruna]], [[Sweden]], and the [[Pilbara]] region of [[Western Australia]]. Additional deposits occur in [[Norway]], [[Germany]], [[Italy]], [[Switzerland]], [[South Africa]], [[India]], and [[Mexico]]. In the [[United States]], it is found in the states of [[New York]] ([[Adirondack Mountains|Adirondack]] region), [[New Jersey]], [[Pennsylvania]], [[North Carolina]], [[Virginia]], [[New Mexico]], [[Colorado]], [[Utah]], and [[Oregon]].
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| − | == Biological occurrences ==
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| − | Crystals of magnetite have been found in some [[bacterium|bacteria]] (such as ''[[Magnetospirillum magnetotacticum]]'') and in the brains of [[bees]], [[termites]], some [[birds]] (including [[pigeon]]s), and [[human being|humans]]. These crystals are thought to be involved in [[magnetoreception]]—the ability to sense the [[Polarity (physics)|polarity]] or [[inclination]] of the Earth's [[magnetic field]]—and to aid 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]] [[Paleoecology|paleoecologist]] [[Heinz Lowenstam]] in the 1960s.
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| − | == Laboratory preparation ==
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| − | Magnetite can be prepared in the laboratory as a [[ferrofluid]] using the [[Massart method]]. It involves mixing [[iron(II) chloride]] and [[iron(III) chloride]] in the presence of [[sodium hydroxide]].
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| − | == Characteristics ==
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| − | This mineral is the most [[magnetic]] of all known naturally occurring minerals. Its [[Curie temperature]] is about 580 °C. Chemically, it dissolves slowly in [[hydrochloric acid]].
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| − | The interactions between magnetite and other iron-rich oxide minerals—such as [[ilmenite]], [[hematite]], and [[ulvospinel]]—have been studied extensively, as the complicated reactions between these minerals and [[oxygen]] influence how magnetite preserves records of the Earth's magnetic field.
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| − | == Uses ==
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| − | * Magnetite is an important ore of iron.
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| − | * [[Lodestone]], a naturally magnetized form of magnetite, played an important role in the study of [[magnetism]] and was used as an early form of magnetic [[compass]].
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| − | * Magnetite typically carries the dominant magnetic signature in rocks, and so it has been a critical tool in [[paleomagnetism]], a science important in discovering and understanding [[plate tectonics]].
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| − | * Changes in the oxygen content of the [[Earth's atmosphere]] can be inferred by studying [[sedimentary rock]]s containing magnetite.
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| − | * [[Igneous rock]]s commonly contain grains of two [[solid solution]]s: one between magnetite and ulvospinel, the other between ilmenite and hematite. A range of oxidizing conditions are found in magmas, and compositions of the mineral pairs are used to calculate how oxidizing the [[magma]] was and the possible evolution of the magma by [[fractional crystallization]].
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| − | ==See also==
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| − | * [[Iron]]
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| − | * [[Magnetism]]
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| − | * [[Mineral]]
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| − | * [[Oxide]]
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| − | ==Notes==
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| − | <references/>
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| − | == References ==
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| − | * Chang', Shih-Bin Robin, and Joseph Lynn Kirschvink. [http://www.gps.caltech.edu/~jkirschvink/pdfs/AnnualReviews89.pdf Magnetofossils, the Magnetization of Sediments, and the Evolution of Magnetite Biomineralization] ''Ann. Rev. Earth Planet. Sci.'' 17:169-95, 1989. Retrieved September 12, 2007.
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| − | * Farndon, John. ''The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks''. London: Lorenz Books, 2006. ISBN 0754815412
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| − | * Klein, Cornelis, and Barbara Dutrow. ''Manual of Mineral Science''. 23rd ed. New York: John Wiley, 2007. ISBN 978-0471721574
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| − | * Lowenstam, Heinz A., and Stephen Weiner. ''On Biomineralization''. New York: Oxford University Press, 2003. ISBN 0195049772
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| − | * Pellant, Chris. ''Rocks and Minerals''. Smithsonian Handbooks. New York: Dorling Kindersley, 2002. ISBN 0789491060
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| − | * Shaffer, Paul R., Herbert S. Zim, and Raymond Perlman. ''Rocks, Gems and Minerals''. Rev. ed. New York: St. Martin's Press, 2001. ISBN 1582381321
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| − | * Mindat.org. [http://www.mindat.org/min-2538.html Magnetite] ''Mindat.org'', 2007. Retrieved September 12, 2007.
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| − | * Mineral Gallery. [http://www.galleries.com/minerals/oxides/magnetit/magnetit.htm The Mineral Magnetite] ''Amethyst Galleries'', 2006. Retrieved September 12, 2007.
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| − | == External links ==
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| − | * [http://webmineral.com/data/Magnetite.shtml Magnetite Mineral Data] ''Webmineral.com.'' Retrieved September 12, 2007.
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| − | * [http://www.astronomycafe.net/qadir/ask/a11651.html Do animals really use magnetism in any interesting way to navigate?] ''Astronomycafe.net.'' Retrieved September 12, 2007.
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| − | [[Category:Physical sciences]]
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| − | [[Category:Earth sciences]]
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| − | [[Category:Geology]]
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| − | [[Category:Minerals]]
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| − | {{credit|120406593}}
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