Cliftonite is a natural form of

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

that occurs as small

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

inclusions in iron-containing meteorites. It typically accompanies

kamacite Kamacite is an alloy of iron and nickel, which is found on Earth only in meteorites. According to the International Mineralogical Association (IMA) it is considered a proper nickel-rich variety of the mineral native iron. The proportion iron:ni ...

, and more rarely

schreibersite Schreibersite is generally a rare iron nickel phosphide mineral, , though common in iron-nickel meteorites. It has been found on Disko Island in Greenland and Illinois. Another name used for the mineral is rhabdite. It forms tetragonal crystals w ...

cohenite Cohenite is a naturally occurring iron carbide mineral with the chemical structure ( Fe, Ni, Co)3 C. This forms a hard, shiny, silver mineral which was named by E. Weinschenk in 1889 after the German mineralogist Emil Cohen, who first described ...

plessite Plessite is a meteorite texture consisting of a fine-grained mixture of the minerals kamacite and taenite found in the octahedrite iron meteorites. It occurs in gaps (its name is derived from the Greek "plythos" meaning "filling"according tMinda ...

. Cliftonite was first considered to be a new form of carbon, then a

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form ( crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...

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. The

Campo del Cielo Campo del Cielo refers to a group of iron meteorites and the area in Argentina where they were found. The site straddles the provinces of Chaco and Santiago del Estero, located north-northwest of Buenos Aires, Argentina and approximately south ...

region of

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

is noted for a crater field containing a group of distinctive iron meteorites.

References

{{reflist Native element minerals Allotropes of carbon Hexagonal minerals Minerals in space group 194