Cliftonite: A proposed origin, and its bearing on the origin of diamonds in meteorites

Cliftonite, a polycrystalline aggregate of graphite with spherulitic structure and cubic morphology, is known in 14 meteorites. Some workers have considered it to be a pseudomorph after diamond, and have used the proposed diamond ancestry as evidence of a meteoritic parent body of at least lunar dimensions. Careful examination of meteoritic samples indicates that cliftonite forms by precipitation within kamacite. We have also demonstrated that graphite with cubic morphology may be synthesized in a Fe-Ni-C alloy annealed in a vacuum. We therefore suggest that a high pressure origin is unnecessary for meteorities which contain cliftonite, and that these meteorities were formed at low pressures. This conclusion is in agreement with other recent evidence.

We also suggest that recently discovered cubes and cubo-octahedra of lonsdaleite in the Canyon Diablo meteorite are pseudomorphs after cliftonite, not diamond, as has previously been suggested.