Graphite

Graphite
Graphite specimen
General
Category	Native element mineral
Formula (repeating unit)	C
Strunz classification	1.CB.05a
Crystal system	Hexagonal
Crystal class	Dihexagonal dipyramidal (6mmm) H-M symbol: (6/m 2/m 2/m)
Space group	P63/mmc
Unit cell	a = 2.461, c = 6.708 [Å]; Z = 4
Identification
Color	Iron-black to steel-gray; deep blue in transmitted light
Crystal habit	Tabular, six-sided foliated masses, granular to compacted masses
Twinning	Present
Cleavage	Basal – perfect on {0001}
Fracture	Flaky, otherwise rough when not on cleavage
Tenacity	Flexible non-elastic, sectile
Mohs scale hardness	1–2
Luster	Metallic, earthy
Streak	Black
Diaphaneity	Opaque, transparent only in extremely thin flakes
Density	2.09–2.23 g/cm3
Optical properties	Uniaxial (–)
Pleochroism	Strong
Solubility	Soluble in molten nickel, warm chlorosulfuric acid
Other characteristics	strongly anisotropic, conducts electricity, greasy feel, readily marks
References

Graphite (pronunciation: /ˈɡræfaɪt/), archaically referred to as plumbago, is a crystalline form of carbon, a semimetal, a native element mineral, and one of the allotropes of carbon. Graphite is the most stable form of carbon under standard conditions. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds.

There are three principal types of natural graphite, each occurring in different types of ore deposits:

Graphite occurs in metamorphic rocks as a result of the reduction of sedimentary carbon compounds during metamorphism. It also occurs in igneous rocks and in meteorites. Minerals associated with graphite include quartz, calcite, micas and tourmaline. In meteorites it occurs with troilite and silicate minerals. Small graphitic crystals in meteoritic iron are called cliftonite.