Maghemite

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Maghemite
Maghemite - Mineralogical Museum Bonn.jpg
Maghemite from Gara Djebilet, Algeria , North Africa
General and classification
chemical formula γ-Fe 2 O 3
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.BB.15 ( 8th edition : IV / C.06)
03/04/07/01
Similar minerals Hematite, magnetite
Crystallographic Data
Crystal system cubic
Crystal class ; symbol pentagon-icositetrahedral; 432
Space group P 4 3 32 (No. 212) or P 4 1 32 (No. 213)Template: room group / 212Template: room group / 213
Lattice parameters a  = 8.35  Å
Formula units Z  = 8
Physical Properties
Mohs hardness 5
Density (g / cm 3 ) calculated: 4.860
Cleavage no
Break ; Tenacity brittle
colour brown, bluish black
Line color brown
transparency opaque to translucent
shine Metal gloss, matt
magnetism strong magnetic

Maghemite ( Maghemite ) is a rather seldom occurring mineral from the mineral class of "oxides and hydroxides" with the idealized chemical composition Fe 2 O 3 , ie it consists of iron in the face-centered cubic γ- modification and oxygen in a ratio of 2: 3.

Maghemite crystallizes in the cubic crystal system and develops exclusively opaque, microcrystalline, massive aggregates of brown, bluish-black color.

Etymology and history

The name maghemite is made up of the first two syllables of the mineral magnetite and the English word hematite for hematite (blood stone), based on its chemical composition and magnetism .

Maghemit was first described in 1927 by PA Wagner. The “Iron Mountain Mine” in Shasta County in the US state of California and the Bushveld complex in South Africa are considered to be the type locality .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the maghemite belonged to the general department of "Oxides with the ratio metal: oxygen = 2: 3 (M 2 O 3 and related compounds)", where it was the only member formed the unnamed group IV / C.06 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies the maghemite under the category of “Oxides with metal: oxygen = 3: 4 and comparable”. This section is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With only medium-sized cations”, where together with Titanomaghemite the “Maghemite group” with the system no . 4.BB.15 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the maghemite to the class of "oxides and hydroxides" and there in the department of "oxides". Here it can be found together with Bixbyit in the unnamed group 04.03.07 within the subdivision of "Simple oxides with a cation charge of 3+ (A 2 O 3 )".

Crystal structure

Maghemite crystallizes cubically in the space group P 4 3 32 (space group no. 212) or P 4 1 32 (no. 213) with the lattice parameter a  = 8.35  Å and 8 formula units per unit cell . Template: room group / 212Template: room group / 213

Modifications and varieties

Maghemite is the cubic, ferrimagnetic modification of iron (III) oxide , while the more common modification is the trigonal antiferromagnetic hematite .

Education and Locations

Maghemite from Gancedo, Chaco Province , Argentina

Maghemite is formed from iron-containing minerals such as magnetite through oxidation at low temperatures . Anatase , goethite , ilmenite , lepidocrocite , marcasite and pyrite appear as accompanying minerals .

So far (as of 2012) almost 130 sites for maghemite are known worldwide. In addition to its type locality "Iron Mountain Mine", Maghemit appeared in California in several places near Lebec in Kern County . In South Africa, the mineral could be found in addition to the Bushveld complex at Onverwacht in the Limpopo province and in the “Vergenoeg Mine” near Vergenoeg in the municipality of Tsantsabane .

In Germany, the mineral appeared in several places near Sinsheim and Katzenbuckel in Baden-Württemberg, on Zeilberg in Bavaria and near Mendig and Kruft in the Eifel in Rhineland-Palatinate.

In Austria, Maghemit has so far only been found on the Untersberg in Salzburg (Austria) and on the "Glücksgrat" on the Habicht in Tyrol.

In Switzerland, the mineral was found near Buechbüel (municipality of Neuhausen am Rheinfall ) and Hasenberg (municipality of Neunkirch ) in the canton of Schaffhausen and at the Irchel in the canton of Zurich.

Other locations include Australia, Bolivia, Brazil, Chile, China, Dominican Republic, India, Israel, Italy, Japan, Cameroon, Canada, Colombia, Cuba, Madagascar, Macedonia, Mexico, Mongolia, Namibia, New Caledonia, New Zealand, Nicaragua, Nigeria, Norway, Portugal, Russia, Saudi Arabia, Sweden, Slovakia, Spain, the Czech Republic, Turkey, the United Kingdom and many other locations in the United States of America.

Occurrence in biology

Maghemite is used together with magnetite in nerve cells of pigeons for orientation in the earth's magnetic field .

See also

literature

Web links

Commons : Maghemite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b IMA List of Minerals; September 2016 (PDF 1.6 MB)
  2. ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  190 (ratio given in the formula Fe 3+ , □) 3 O 4 is incorrect).
  3. ↑ a b Maghemite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001. ( PDF 68.5 kB )
  4. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp.  515 (first edition: 1891).
  5. ↑ Mineral Atlas: Maghemite
  6. ↑ Mindat - Number of localities for Maghemite
  7. ↑ Mindat - Maghemite