Graphite - Encyclopedia

    Class : Elements
    Subclass : Non-metals
    Crystal system : Hexagonal
    Chemistry : C
    Rarity : Common


Graphite is, with diamond, lonsdaleite and chaoite, a polymorph of carbon. Graphite has a sheet structure. Each layer is made up of the juxtaposition of rings with six carbon atoms, and connected to the others by very weak Van der Walls forces, at the origin of the good cleavage according to {001} of this mineral. Graphite is usually present in metamorphic rocks coming from sediments rich in organic matter, sometimes in magmatic rocks having assimilated carbonaceous materials, rarely in granitic pegmatites. Its name comes from the Greek graphein (to write) due to its ancient use as a pencil. It is a black mineral with a metallic luster, staining the fingers because of its low hardness and its strong micaceous cleavage which causes it to disintegrate into fine flakes. Tabular hexagonal crystals, sometimes bordered by distinct isoscelohedra, are rare, usually centimetric, but can exceptionally reach 20 cm. Graphite most often occurs in stacks of shapeless micaceous lamellae, in irregular foliated masses, or in masses of amorphous appearance ; it is also earthy or in globular aggregates with a radiated structure. The industrial applications of graphite are numerous. If its use as pencil lead, inaugurated around 1550, is today anecdotal, its specific properties mean that it is found in numerous industrial sectors : lubricants (thanks to its low hardness of 1 to 2), refractories (chemical crucible, thanks to have a very high melting point: 4492°C), nuclear industry (neutron retarders). The production of synthetic graphite, however, clearly exceeds mining production.

Main photo : Graphite from Rhein Property, Amity, New York, USA © Pasquale Antonazzo

Franklin Graphite, Sussex County, New Jersey, USA © Rock Currier
Graphite and diopside from Merelani Hills, Tanzania © John A. Jaszczak
Graphite from Verity Property, British Columbia, Canada © Tony Peterson
Graphite pseudomorph after diamond from Ozernaya Mount, Russia © John A. Jaszczak

Graphite in the World

Centimetric graphite crystals are known, notably in Finland (Ersby and Storgard) and in Franklin (New Jersey), but also in Merelani Hills (Tanzania) where they are associated with diopside and tanzanite. Large masses have been extracted in Sri Lanka, Finland and Madagascar since the dawn of time, and especially in Siberia in the famous Alibert mine where masses of exceptional size and quality are known.

Graphite in France

In France, graphite is reported in many localities, notably Ste-Marie-aux-Mines (Haut-Rhin), at the Bois-de-la-Roche and Floquerie quarries (Loire-Atlantique), at Collioure ( Pyrénées-Orientales), etc...

Twinning

Twins are known for this mineral species. Diamond crystals can be completely replaced by graphite.

Fakes and treatments

No fakes recorded for this mineral species.



Hardness : 1 to 2
Density : 2.09 to 2.23
Fracture : Micaceous
Streak : Black to gray


TP : Opaque
RI : -
Birefringence : -
Optical character : Uniaxial -
Pleochroism : None
Fluorescence : None


Solubility : Insoluble

Magnetism : DiamagneticRadioactivity : None

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