Chemistry:Cliftonite
| 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 |
| |re|er}} | 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.
References
- ↑ 1.0 1.1 Cliftonite. Mindat.org.
- ↑ 2.0 2.1 Brett, R; Higgins, GT (1967). "Cliftonite in meteorites: A proposed origin". Science 156 (3776): 819–20. doi:10.1126/science.156.3776.819. PMID 17780301. Bibcode: 1967Sci...156..819B. http://library.worldtracker.org/Science/Science%20Magazine/science%20magazine%201966-1967/root/data/Science%201966-1967/pdf/1967_v156_n3776/1722017.pdf.
- ↑ 3.0 3.1 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. Bibcode: 1969GeCoA..33.1473B.
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