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Kamacite

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Title: Kamacite  
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Subject: Meteoric iron, Hexahedrite, Ataxite, Octahedrite, Native element minerals
Collection: Iron Minerals, Meteorite Minerals, Native Element Minerals, Nickel Minerals
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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
Strunz classification 01.AE.05
Identification
Formula mass 56.13
Color Iron black, steel gray
Crystal habit Massive - uniformly indistinguishable crystals forming large masses
Crystal system Isometric (4/m 3 2/m) Space Group: Fm3m
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 [1]

Kamacite is an alloy of iron and nickel, which is found on earth only in meteorites. The proportion iron:nickel is between 90:10 to 95:5; small quantities of other elements, such as cobalt or carbon may also be present. The mineral 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 centimetres (36.2×21.3×9.1 in).[2]

See also

References

  1. ^ Kamacite Mineral Data
  2. ^ P. C. Rickwood (1981). "The largest crystals". American Mineralogist 66: 885–907. 
  • Mason B., 1962: Meteorites. J. Wiley & Sons, New York
Kamacite and taenite after taenite, exhibiting the octahedral structure of taenite, Nantan (Nandan) iron meteorite, 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.


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