|Category||Native element mineral|
Dihexagonal dipyramidal (6/mmm) |
H-M symbol: (6/m 2/m 2/m)
|Crystal habit||Octahedra, cubes, cubo-octahedra, cubo-dodecahedra; isolated or aggregated, ca. 20 μm in size|
|Mohs scale hardness||1|
Cliftonite is a natural form of graphite that occurs as small octahedral inclusions in iron-containing meteorites, such as Campo del Cielo. It typically accompanies kamacite, and more rarely schreibersite, cohenite or plessite.
Cliftonite was first considered to be a new form of carbon, then a pseudomorph of graphite after diamond, and finally reassigned to a pseudomorph of graphite after kamacite. Cliftonite is typically observed in minerals that experienced high pressures. It can also be synthesized by annealing an Fe-Ni-C alloy at ambient pressure for several hundred hours. The annealing is carried out in two stages: first a mixture of cohenite and kamacite is formed in air at ca. 950 °C; it is then partly converted to cliftonite in vacuum at ca. 550 °C.
- Cliftonite. Mindat.org.
- Brett, R; Higgins, GT (1967). "Cliftonite in meteorites: A proposed origin" (PDF). Science. 156 (3776): 819–20. doi:10.1126/science.156.3776.819. PMID 17780301.
- Brett, Robin; Higgins, G.T. (1969). "Cliftonite: A proposed origin, and its bearing on the origin of diamonds in meteorites". Geochimica et Cosmochimica Acta. 33 (12): 1473. doi:10.1016/0016-7037(69)90151-3.
- graphite. Encyclopædia Britannica Online.