Kamacite

Kamacite
Widmanstätten pattern showing the two forms of nickel-iron minerals, kamacite and taenite
General
Category	Meteorite mineral
Formula (repeating unit)	α-(Fe,Ni); Fe0+0.9Ni0.1
Crystal system	Isometric (4/m 3 2/m) Space Group: Fm3m
Identification
Formula mass	56.13
Color	Iron black, steel gray
Crystal habit	Massive - uniformly indistinguishable crystals forming large masses
Cleavage	Indistinct
Fracture	Hackly - Jagged, torn surfaces, (e.g. fractured metals).
Mohs scale hardness	4
Luster	metallic
Streak	gray
Specific gravity	7.9
Other characteristics	non-radioactive, magnetic, non-fluorescent.
References

Kamacite is a mineral. It is an alloy of iron and nickel, usually in the proportions of 90:10 to 95:5 although impurities such as cobalt or carbon may be present. On the surface of Earth, it occurs naturally only in meteorites. It has a metallic luster, is gray and has no clear cleavage although the structure is isometric-hexoctahedral. Its density is around 8 g/cm³ and its hardness is 4 on the Mohs scale. It is also sometimes called balkeneisen.

The name was coined in 1861 and is derived from the Greek kamask (lath or beam). It is a major constituent of iron meteorites (octahedrite and hexahedrite types). In the octahedrites it is found in bands interleaving with taenite forming Widmanstätten patterns. In hexahedrites, fine parallel lines called Neumann lines are often seen, which are evidence for structural deformation of adjacent kamacite plates due to shock from impacts.

At times kamacite can be found so closely intermixed with taenite that it is difficult to distinguish them visually, forming plessite. The largest documented kamacite crystal measured 92×54×23 cm.

See also: list of minerals

References

• Mason B., 1962: Meteorites. J. Wiley & Sons, New York

Kamacite, Nantan (Nandan) iron meteorites, Nandan County, Guangxi Zhuang Autonomous Region, China. Size: 4.8×3.0×2.8 cm. The Nantan irons, a witnessed fall in 1516, have a composition of 92.35% iron and 6.96% nickel.