Magnetite: Difference between revisions
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magnetite is a magnetic mineral |
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:''Magnetite is not to be confused with [[Magnesite]] or [[Magnemite]].'' |
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{{Infobox mineral |
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| name = Magnetite |
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| category = |
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| boxwidth = |
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| image = Magnetite Russia.jpg |
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| imagesize = |
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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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| fusibility = |
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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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hehe |
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'''Magnetite''' is a [[ferrimagnetism|ferrimagnetic]] [[mineral]] with chemical formula '''[[Iron|Fe]]<sub>3</sub>[[Oxygen|O]]<sub>4</sub>''', one of several [[iron oxide]]s and a member of the [[spinel]] group. The chemical [[IUPAC]] name is '''iron(II,III) oxide''' and the common chemical name '''ferrous-ferric oxide'''. The formula for magnetite may also be written as FeO.Fe<sub>2</sub>O<sub>3</sub>, which is one part [[wüstite]] (FeO) and one part [[hematite]] (Fe<sub>2</sub>O<sub>3</sub>). This refers to the different oxidation states of the iron in one structure, not a [[solid solution]]. |
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The [[Curie temperature]] of magnetite is about 580°C. Magnetite is the most [[magnetic]] of all the naturally occurring minerals on [[Earth]], and these magnetic properties led to [[lodestone]] being used as an early form of magnetic [[compass]]. 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]]. The relationships between magnetite and other iron-rich oxide minerals such as [[ilmenite]], [[hematite]], and [[ulvospinel]] have been much studied, as the complicated [[Metamorphic reaction|reaction]]s between these minerals and [[oxygen]] influence how and when magnetite preserves records of the Earth's magnetic field. |
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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 [[mineral redox buffer|buffer]] that can control oxygen [[fugacity]]. Commonly [[igneous rock]]s contain grains of two [[solid solution]]s, one between magnetite and ulvospinel and the other between [[ilmenite]] and [[hematite]]. Compositions of the mineral pairs are used to calculate how oxidizing was the [[magma]] (i.e., the [[oxygen]] [[fugacity]] of the magma): a range of [[Mineral redox buffer|oxidizing conditions]] are found in magmas and the oxidation state helps to determine how the magmas might evolve by [[fractional crystallization]]. |
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Small grains of magnetite occur in almost all [[igneous rocks]] and [[metamorphic rocks]]. Magnetite also occurs in many [[sedimentary rocks]], including [[banded iron formation]]s. In many [[igneous rock]]s, magnetite-rich and [[ilmenite]]-rich grains occur that precipitated together from [[magma]]. Magnetite also is produced from [[peridotite]]s and [[dunite]]s by [[serpentinite|serpentinization]]. |
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Magnetite is a valuable source of [[iron ore]]. It dissolves slowly in [[hydrochloric acid]]. |
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== Distribution of deposits == |
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Magnetite is sometimes found in large quantities in beach sand. Such [[mineral sand]]s or [[iron sand]]s or [[black sand]]s 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. |
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Huge deposits have been found in [[banded iron formation]]s. These [[sedimentary rock]]s have been used to infer changes in the oxygen content of the atmosphere of the Earth. |
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Large deposits of magnetite also are found in [[Kiruna]], [[Sweden]], the [[Pilbara]] region in [[Western Australia]], and in the [[Adirondack Mountains|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 km², with the highest dune at over 2000 m above the desert floor. The sand contains 10% magnetite[http://www.321gold.com/editorials/moriarty/moriarty070505.html]. |
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== Biological occurrences == |
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Crystals of magnetite have been found in some [[bacterium|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 (physics)|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. |
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The study of [[biomagnetism]] began with the discoveries of [[Caltech]] [[Paleoecology|paleoecologist]] [[Heinz Lowenstam]] in the 1960s. |
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== Preparation as a ferrofluid == |
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Magnetite can be prepared in the laboratory as a [[ferrofluid]] in the [[Massart method]] by mixing [[iron(II) chloride]] and [[iron(III) chloride]] in the presence of [[sodium hydroxide]]. |
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==See also== |
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* [[Ferrite]] |
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* [[Hematite]] |
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* [[Wüstite]] |
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* [[Mineral redox buffer]] |
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* [[Magnesia (mineral)|Magnesia]] |
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* [[Maghemite]] |
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* [[Bluing (steel)]] is a process in which steel is partially-protected against rust by a layer of magnetite. |
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== References == |
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=== Mineralogy related === |
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* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., Wiley, ISBN 0-471-80580-7 |
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* [http://webmineral.com/data/Magnetite.shtml Webmineral data] |
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* [http://www.galleries.com/minerals/oxides/magnetit/magnetit.htm Mineral galleries] |
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=== Biology related === |
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* Heinz A. Lowenstam and Stephen Weiner, ''On Biomineralization'', Oxford University Press, USA (1989) ISBN 0-19-504977-2 |
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* 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 [http://www.gps.caltech.edu/~jkirschvink/pdfs/AnnualReviews89.pdf PDF file] |
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* [http://www.astronomycafe.net/qadir/ask/a11651.html Bio-magnetics] |
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* [http://it.wikipedia.org/wiki/Batteri_magnetotattici Magnetic bacteria (Italian)] |
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=== Mining related links === |
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* [http://abandonedmines.net History of Magnetite Mining in the NJ Highlands] |
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* [http://crownminerals.med.govt.nz/minerals/gnsmaps/map-metmins.html Magnetite mining in New Zealand] |
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* [http://www.santacruzpl.org/history/work/miner3.shtml Magnetite mining in Santa Cruz] |
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* [http://www.321gold.com/editorials/moriarty/moriarty070505.html Peruvian sand dunes] |
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<!--Categories--> |
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[[Category:Magnetism]] |
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[[Category:Iron compounds]] |
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[[Category:Iron minerals]] |
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[[Category:Oxides]] |
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[[Category:Oxide minerals]] |
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[[Category:Ferromagnetic materials]] |
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<!--Interwiki--> |
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[[cs:Magnetit]] |
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[[de:Magnetit]] |
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[[et:Magnetiit]] |
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[[es:Magnetita]] |
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[[fr:Magnétite]] |
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[[he:מגנטיט]] |
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[[lt:Magnetitas]] |
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[[nl:Magnetiet]] |
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[[ja:磁鉄鉱]] |
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[[no:Magnetitt]] |
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[[pl:Magnetyt]] |
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[[ru:Магнетит]] |
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[[uk:Магнетит]] |
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Revision as of 17:25, 2 October 2007
magnetite is a magnetic mineral
hehe