Graphite in Meteorites

Graphite occurs in many meteorites. One of the most interesting and photogenic examples being the polycrystalline variety "cliftonite" in the Campo de Cielo and several other meteorites.

Click here to see an amazing photo of graphite nodules from the Nantan, China meteorite.


Shiny "cuboctahedral" and "octahedral" graphite, variety cliftonite, (to 0.5 mm) in kamacite in the Campo de Cielo meteorite.	Cluster of shiny "octahedral" crystals of graphite variety cliftonite, (to 0.5 mm) in corroded kamacite from the Canyon Diablo Meteorite, Arizona.

Because of their shapes, this type of graphite was thought to be a pseudomorph after diamond. It is now accepted that they are not pseudomorphs after diamond. Brett & Higgins (1969) conclude that cliftonite was formed by decomposition of cohenite with subsequent diffusion of carbon to nucleation sites. The external morphology of the cliftonite was determined by the crystallographic structure of the host metal (kamacite). Natural and artificial graphite after diamond has the (0001) graphite planes aligned parallel to diamond (111) planes, which apparently is not the case in cliftonite where the growth texture is more spherulitic.

REFERENCES

Brett, R. & Higgins, G.T. (1969) "Cliftonite: A proposed origin, and its bearing on the origin of diamonds in meteorites." Geochimica Cosmochim Acta 33 1473-1484.

Deines, P. & Wickman, F.E. (1975) "A contribution to the stable carbon isotope geochemistry of iron meteorites." Geochimica et Cosmochimica Acta 39 574-557.

Fletcher, L. (1887) "On a meteoric iron found in 1884 in the sub-district of Youndegin, Western Australia, and containing Cliftonite, a cubic form of graphitic carbon." The Mineralogical Magazine 7 121-130.

Ramdohr, P. (1972) "Neue Formen meteoritischen Graphits und mogliche Beziehungen zum Cliftonit" Die Naturwissenschaften 58 613-615.

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