Cliftonite
Cliftonite is a natural form of graphite that occurs as small octahedral inclusions in iron-containing meteorites,[4] such as Campo del Cielo. It typically accompanies kamacite, and more rarely schreibersite, cohenite or plessite.[3]
| Cliftonite | |
|---|---|
| General | |
| Category | Native element mineral |
| Formula (repeating unit) | C |
| Crystal system | Hexagonal |
| Crystal class | Dihexagonal dipyramidal (6/mmm) H-M symbol: (6/m 2/m 2/m) |
| Space group | P63/mmc |
| Identification | |
| Color | Gray |
| Crystal habit | Octahedra, cubes, cubo-octahedra, cubo-dodecahedra; isolated or aggregated, ca. 20 μm in size |
| Mohs scale hardness | 1 |
| Luster | Sub-metallic |
| Streak | gray |
| References | [1][2][3] |
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.[1] 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.[2]
References
- 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.