Cohenite
- Cementite and cementite
- Iron carbide
Cohenite is a rarely occurring meteoritic mineral from the mineral class of " Element Minerals ". It crystallizes in the orthorhombic crystal system with the idealized composition Fe3C. Since the mineral in nature but often contains small admixtures of nickel and cobalt, the formula is often given with (Fe, Ni, Co ) 3C. The elements in brackets can be represented each other, but are always in the same proportions to the carbon.
Cohenite is also in thin layers of opaque (opaque ) and developed only millimeter-sized, imperfect tabular to acicular crystals or dendritic eutectic intergrowths with iron. Fresh samples are of zinnweißer color with metallic luster, but oxidize the crystal faces after some time and takes on the color a bright bronze to golden- yellow hue.
In metallurgy, the compound Fe3C cementite (formerly: cementite ) or iron carbide known and an important ingredient in white and raw cast iron and steel.
Special Features
Cohenite is a very brittle and strongly magnetic mineral.
Under terrestrial conditions, the mineral kbar is only stable at pressures above 40, which corresponds to a depth of about 120 km. On the surface, it breaks down very slowly in the minerals kamacite and graphite.
Etymology and history
Cohenite was first discovered in Magura meteorite in the former Hungarian and now part of Slovakia Orava county. This has been described in 1889 by mineral Ernst Weinschenk, who named it after the German mineralogist and petrographers Emil Cohen. This was dedicated to his work, mainly the structure of iron meteorites and minerals contained in them.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the cohenite where he along with Haxonit, Hongquiit, Isovit, Khamrabaevit, Niobocarbid, tantalum and Tongbait the unnamed group belonged to the department of " metals, alloys and intermetallic compounds ," I/A.09 formed.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the cohenite other hand, in the newly defined division of the " Metallic carbon, nitrogen and phosphorus compounds " one. This is also further subdivided by the connection characterizing connection Spartans, so that the mineral is found according to its composition in the subdivision of the " Carbide ", where it forms the unnamed group 1.BA.05 the only member.
The mostly commonly used in English-speaking classification of minerals according to Dana assigns the cohenite also in the class of " Element Minerals " and then in the same department. Here he is with Haxonit and Isovit in the unnamed group 01:01:16 within the subdivision " elements: except the platinum group metallic elements " to be found.
Education and Locations
Cohenite is part of iron meteorites and in enstatite chondrites. On Earth, it is only found in igneous rocks, which were reduced by secondary penetration into coal seams, such as Am Buehl at Kassel in Germany and in Qeqertarsuaq in Greenland. Accompanying minerals occur under other native iron, schreibersite, troilite and wustite.
The mineral in various meteorites, so among other things in the Allan Hills 84001 in Antarctica, Campo del Cielo, Argentina, Cranbourne meteorite in Australia, Uruacu in the Brazilian state of Goiás, Ulasitai meteorite in the Chinese autonomous district Changji, Toluca meteorite was found in Mexico, South Dahna meteorite in the Rub al Khali in Saudi Arabia, Nagyvázsony meteorite in the Hungarian Bakony and in several, found in the United States of America meteorites ( Canyon Diablo, Goose Lake Pulaski County, Las Vegas and Odessa).
Furthermore, cohenite also found in Bukowno and Morasko meteor in Poland, at Chatanga ( Khatanga ) and in the coal mine " No. 45 " at Kopeisk in Russia.
Crystal structure
Cohenite crystallizes in the orthorhombic space group Pnma ( Raumgruppen-Nr. 62) with the lattice parameters a = 5.09 Å; b = 6.75 Å and c = 4.52 Å and four formula units per unit cell.