| Cliftonite | |
| Category: | Native element mineral |
| Formula: | C |
| System: | Hexagonal |
| Class: | Dihexagonal dipyramidal (6/mmm) H-M symbol: (6/m 2/m 2/m) |
| Symmetry: | P63/mmc |
| Color: | Gray |
| Habit: | Octahedra, cubes, cubo-octahedra, cubo-dodecahedra; isolated or aggregated, ca. 20 μm in size |
| Mohs: | 1 |
| Luster: | Sub-metallic |
| Streak: | gray |
| References: | [1] [2] [3] |
Cliftonite is a natural form of graphite that occurs as small octahedral inclusions in iron-containing meteorites. It typically accompanies kamacite, and more rarely schreibersite, cohenite or plessite.[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]
The Campo del Cielo region of Argentina is noted for a crater field containing a group of distinctive iron meteorites.