Graphite

Crestmore, Riverside Co., California, USA © John Jaszczak

Chemical Formula: C
Locality: Ticonderoga, New York. Madagascar and Ceylon.
Name Origin: From the Greek, graphein, “to write.”

Graphite is made almost entirely of carbon atoms, and as with diamond, is a semimetal native element mineral, and an allotrope 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. Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is difficult to ignite.

Occurrence

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.

According to the United States Geological Survey (USGS), world production of natural graphite in 2012 was 1,100,000 tonnes, of which the following major exporters are: China (750 kt), India (150 kt), Brazil (75 kt), North Korea (30 kt) and Canada (26 kt). Graphite is not mined in the United States, but U.S. production of synthetic graphite in 2010 was 134 kt valued at $1.07 billion.

Physical Properties

Cleavage: {0001} Perfect
Color: Iron black, Dark gray, Black, Steel gray.
Density: 2.09 – 2.23, Average = 2.16
Diaphaneity: Opaque
Fracture: Sectile – Curved shavings or scrapings produced by a knife blade, (e.g. graphite).
Hardness: 1.5-2 – Talc-Gypsum
Luminescence: Non-fluorescent.
Luster: Sub Metallic
Magnetism: Nonmagnetic
Streak: black

Photos :

This sample of graphite is displayed in the Smithsonian Museum of Natural History. This sample is graphite with calcite from Ticonderoga, New York. The sample is about 15 cm wide.
Graphite 8.1×4.6×1.6 cm Kilmar, Grenville Twp., Quebec, Canada Copyright ©  David K. Joyce Minerals
This sample of graphite is displayed in the Smithsonian Museum of Natural History. The sample at left is about 12 cm across and is from Canada.
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