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利用者:Bloody panda/sandbox

磁赤鉄鉱
分類 Oxide minerals
シュツルンツ分類 04.BB.15
化学式 γ-Fe2O3
結晶系 Cubic with a tetragonal supercell
対称 Isometric tetartoidal
H-M symbol: (2 3)
Space group: P 213
単位格子 a = 8.33 Å; Z = 8 or a = 8.35 Å c = 24.99 Å; Z = 32 for tetragonal supercell
晶癖 Rarely as minute octahedral crystals, or acicular overgrowths; commonly as coatings on or replacements of magnetite; massive.
へき開 None
断口 Subconchoidal
モース硬度 5
光沢 Dull
Brown, bluish black; brown to yellow in transmitted light; white to bluish gray in reflected light.
条痕 Brown
透明度 Opaque, transparent in thin fragments
比重 4.860 (calculated)
光学性 Isotropic
その他の特性 Strongly magnetic
文献 [1][2][3]
プロジェクト:鉱物Portal:地球科学
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赤磁鉄鉱(せきじてっこう、Maghemite、マグヘマイト)は、酸化鉱物の一種。化学組成は (Fe2O3, γ-Fe2O3)。磁鉄鉱と同じく、結晶系等軸晶系スピネルグループの鉱物。 Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same structure as magnetite, that is, it is spinel ferrite and is also ferrimagnetic.

Maghemite can be considered as an Fe(II)-deficient magnetite with formula [4] where represents a vacancy, indicates tetrahedral positioning and octahedral.

Occurrence

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Maghemite forms by weathering or low-temperature oxidation of spinels containing iron(II) such as magnetite or titanian magnetite. It occurs as widespread yellow pigment in terrestrial sediments and soils. It is associated with magnetite, ilmenite, anatase, pyrite, marcasite, lepidocrocite and goethite.[1]

Maghemite was named in 1927 for an occurrence at the Iron Mountain mine, northwest of Redding, Shasta County, California.[3] The name alludes to somewhat intermediate character between MAGnetite and HEMatite. It is blue with a grey shade, white, or brown.[5] It has isometric crystals.[2] Maghemite is formed by the topotactic oxidation of magnetite.

Cation distribution

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There is experimental[6] and theoretical[7] 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.

Electronic structure

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Maghemite is a semiconductor with a bandgap of around 2 eV,[8] although the precise value of the gap depends on the electron spin.[7]

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.[9]

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.[10]

See also

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References

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  1. ^ a b Handbook of Mineralogy
  2. ^ a b Maghemite on Mindat
  3. ^ a b Maghemite on Webmineral
  4. ^ R. M. Cornell and Udo Schwertmann: The iron oxides: structure, properties, reactions, occurrences, and uses, pp 32. Wiley-VCH, 2003
  5. ^ Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig: "Dana's new mineralogy", pp. 229-230. John Wiley & Sons, 1997
  6. ^ C. Greaves, J. Solid State Chem. 49 325 (1983)
  7. ^ a b 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
  8. ^ M. I. Litter and M. A. Blesa Can. J. Chem. 70, 2502 (1992)
  9. ^ 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
  10. ^ 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)