Cliftonite

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Cliftonite
General
Category Native element mineral
Formula
(repeating unit)
C
Crystal symmetry Hexagonal dihexagonal dipyramidal
H-M symbol: (6/m 2/m 2/m)
Space group: P 63/mmc
Identification
Color Gray
Crystal habit Octahedra, cubes, cubo-octahedra, cubo-dodecahedra; isolated or aggregated, ca. 20 μm in size
Crystal system Hexagonal
Mohs scale hardness 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,[4] such as Campo del Cielo. 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 re-assigned 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[edit]

  1. ^ a b Cliftonite. Mindat.org.
  2. ^ a b 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. 
  3. ^ a b 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. 
  4. ^ graphite. Encyclopædia Britannica Online.