Maghemite

Maghemite ( maghemite ) is a rarely occurring mineral from the mineral class of oxides and hydroxides. It crystallizes in the cubic crystal system with the idealized composition Fe2O3, that is made of iron in the face centered cubic γ - modification and oxygen in the ratio of 2: 3

Maghemite is opaque and developed exclusively microcrystalline, massive aggregates of brown, bluish black color.

Etymology and history

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

Maghemite 1927 was first described by PA Wagner. Type locality as the "Iron Mountain Mine " in Shasta county located in the U.S. state of California and the Bushveld complex in South Africa apply.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the maghemite belonged to the general ward of the " oxides with the ratio of metal: Oxygen = 2: 3 ( M2O3 and related compounds ) ," where he was the only member of the unnamed group IV/C.06 formed.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the maghemite, however, in the department of " Oxides with metal: oxygen = 3: 4 and comparable " one. This department is also further divided according to the relative size of the cations involved, so that the mineral is "With only medium-sized cations " to find according to its composition in the subdivision where it together with Titanomaghemit the " maghemite group " with the system no. 4.BB.15 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the maghemite in the class of " oxides and hydroxides " and there in the department of " oxides ". Here it is to find "simple oxides with a cation charge of 3 ( A2O3 ) " along with Bixbyite in the unnamed group 04:03:07 within the subdivision of.

Modifications and varieties

Maghemite is cubic, ferrimagnetic modification of iron (III ) oxide, whereas the more widely used modification of the trigonal antiferromagnetic hematite.

Education and Locations

Maghemite is formed by oxidation at low temperatures of iron -bearing minerals such as magnetite. Accompanying minerals magnetite occur, among other things still anatase, goethite, ilmenite, lepidocrocite, marcasite and pyrite.

Worldwide, so far (as of 2012) almost 130 localities for maghemite known. Apart from its type locality "Iron Mountain Mine " maghemite occurred among others still at several points in Lebec in Kern County in California. In South Africa, the mineral could be found except in the Bushveld complex even at Onverwacht in the province of Limpopo and in the " Vergenoeg Mine" at Vergenoeg in the community Tsantsabane.

In Germany the mineral occurred among others in several places in Sinsheim and the cat's back in Baden- Württemberg, the Zeilberg in Bavaria and in Mendig and Kruft in the Eifel region of Rhineland- Palatinate.

In Austria, maghemite found previously only on the lower mountain in Salzburg ( Austria ) and the " Glücksgrat " the hawk in Tyrol.

In Switzerland, the mineral in Buechbüel could (municipality Neuhausen Rhine Falls ) and Hasenbergstraße (municipality Neunkirch ) are found in the canton of Schaffhausen and the Irschel in the canton of Zurich.

Other localities lie including 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, Switzerland, Turkey, the United Kingdom and many other places in the United States of America.

Crystal structure

Maghemite crystallized cubic in space group P4332 ( Raumgruppen-Nr. 212) or P4132 ( Raumgruppen-Nr. 213 ) with the lattice parameters a = 8.35 Å, and eight formula units per unit cell.

Occurrence in biology

Maghemite is used together with magnetite in nerve cells of pigeons for orientation in the geomagnetic field.