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| {{distinguish|Magnesite|Magnetite}}
| | 53 year-old Real House Agent Odis from Alert Bay, loves house brewing, property developers in singapore and aquariums. Wants to travel and was motivated after paying a visit to Historical Monuments at Makli.<br><br>my web site [http://www.hondaforum.de/forum/member.php?u=64508-QRXC http://www.hondaforum.de] |
| {{infobox mineral
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| | name = Maghemite
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| | category = [[Oxide minerals]]
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| | boxwidth =
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| | boxbgcolor =
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| | image = Maghemita.jpg
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| | imagesize =
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| | alt =
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| | caption = Maghemite from [[Gancedo]], [[Chaco Province]], Argentina
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| | formula = γ-Fe<sub>2</sub>O<sub>3</sub>
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| | strunz = 04.BB.15
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| | dana =
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| | symmetry = Isometric tetartoidal<br/>[[H-M symbol]]: (2 3)<br/>[[Space group]]: P 2<sub>1</sub>3
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| | unit cell = a = 8.33 Å; Z = 8 or a = 8.35 Å c = 24.99 Å; Z = 32 for tetragonal supercell
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| | molweight =
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| | color = Brown, bluish black; brown to yellow in transmitted light; white to bluish gray in reflected light.
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| | colour =
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| | habit = Rarely as minute octahedral crystals, or acicular overgrowths; commonly as coatings on or replacements of magnetite; massive.
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| | system = [[Cubic crystal system|Cubic]] with a tetragonal supercell
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| | twinning =
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| | cleavage = None
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| | fracture = Subconchoidal
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| | tenacity =
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| | mohs = 5
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| | luster = Dull
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| | streak = Brown
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| | diaphaneity = Opaque, transparent in thin fragments
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| | gravity = 4.860 (calculated)
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| | density =
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| | polish =
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| | opticalprop = Isotropic
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| | refractive =
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| | diagnostic =
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| | solubility =
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| | other = Strongly magnetic
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| | alteration =
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| | references = <ref name=Handbook>[http://rruff.geo.arizona.edu/doclib/hom/maghemite.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-2533.html Maghemite on Mindat]</ref><ref name=Webmin>[http://webmineral.com/data/Maghemite.shtml Maghemite on Webmineral]</ref>
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| }}
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| '''Maghemite''' (Fe<sub>2</sub>O<sub>3</sub>, γ-Fe<sub>2</sub>O<sub>3</sub>) is a member of the family of [[iron oxide]]s. It has the same structure as [[magnetite]], that is, it is [[spinel]] [[Ferrite (magnet)|ferrite]] and is also [[ferrimagnetic]].
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| ''Maghemite'' can be considered as an Fe(II)-deficient magnetite with formula
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| <math>(\mathrm{Fe}^\mathrm{III}_8)_A[\mathrm{Fe}^{\mathrm{III}}_{40/3}\square_{8/3}]_B\mathrm{O}_{32}</math> <ref>R. M. Cornell and Udo Schwertmann: The iron oxides: structure, properties, reactions, occurrences, and uses, pp 32. Wiley-VCH, 2003</ref> where
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| <math>\square</math> represents a vacancy, <math>A</math> indicates tetrahedral positioning and <math>B</math> octahedral.
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| ==Occurrence==
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| Maghemite forms by [[weathering]] or low-temperature [[oxidation]] of [[spinel]]s containing iron(II) such as magnetite or titanian magnetite. It occurs as widespread yellow [[pigment]] in terrestrial [[sediment]]s and soils. It is associated with magnetite, [[ilmenite]], [[anatase]], [[pyrite]], [[marcasite]], [[lepidocrocite]] and [[goethite]].<ref name=Handbook/>
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| Maghemite was named in 1927 for an occurrence at the Iron Mountain mine, northwest of [[Redding, California|Redding]], [[Shasta County, California]].<ref name=Webmin/> The name alludes to somewhat intermediate character between MAGnetite and HEMatite. It is blue with a grey shade, white, or brown.<ref>Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig: "[[James Dwight Dana|Dana's]] new mineralogy", pp. 229-230. John Wiley & Sons, 1997</ref> It has [[Cubic crystal system|isometric]] crystals.<ref name=Mindat/> Maghemite is formed by the [[topotactic]] [[oxidation]] of [[magnetite]].
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| ==Cation distribution==
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| There is experimental<ref>C. Greaves, J. Solid State Chem. 49 325 (1983)</ref> and theoretical<ref name=jpcm2011>R. Grau-Crespo, A. Y. Al-Baitai, I. Saaudoune, N.H. de Leeuw, "Vacancy ordering and electronic structure of γ -Fe2O3 (maghemite): a theoretical investigation" J. Phys. Condens. Matter 22, 255401 (2010) http://iopscience.iop.org/0953-8984/22/25/255401</ref> evidence that Fe(III) cations and vacancies tend to be ordered in the octahedral sites, in a way that maximizes the homogeneity of the distribution and therefore minimizes the [[electrostatic energy]] of the [[crystal]].
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| ==Electronic structure==
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| Maghemite is a [[semiconductor]] with a [[bandgap]] of around 2 eV,<ref>M. I. Litter and M. A. Blesa Can. J. Chem. 70, 2502 (1992)</ref> although the precise value of the gap depends on the electron [[spin (physics)|spin]].<ref name=jpcm2011/>
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| ==Applications==
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| Maghemite exhibits [[ferrimagnetic]] ordering with a high [[Néel temperature]] (~950 K), which together with its low cost and chemical stability led to its wide application as a magnetic pigment in electronic recording media since the 1940s.<ref>R. Dronskowski, "The little maghemite story: A classic functional material" Adv. Funct. Mater. 11, 27 (2001) http://onlinelibrary.wiley.com/doi/10.1002/chin.200125209/abstract</ref>
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| Maghemite [[nanoparticles]] are also used in [[biomedicine]], because they are biocompatible and non-toxic to humans, while their magnetism allows remote manipulation with external fields.<ref>Q. A. Pankhurst, J. Connolly, S. K. Jones and J. Dobson, "Applications of magnetic nanoparticles in biomedicine" J. Phys. D: Appl. Phys. 36, R167 (2003)</ref>
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| == See also ==
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| * [[List of Minerals]]
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| ==References==
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| {{reflist}}
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| [[Category:Iron minerals]]
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| [[Category:Oxide minerals]]
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| [[Category:Ilmenite group]]
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53 year-old Real House Agent Odis from Alert Bay, loves house brewing, property developers in singapore and aquariums. Wants to travel and was motivated after paying a visit to Historical Monuments at Makli.
my web site http://www.hondaforum.de