Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Fernando Gomez
Photo courtesy of Roger Weller
Discovery of Graphite
Graphite was discover before the early 1500’s, where there was a large amount of
graphite at Seathwaite Fell near to Borrowdale in Cumbria, England. The people
who lived in there used this mineral for marking sheeps. They found that it was
a very useful tool for marking them, since graphite it’s a black mineral.
Where does the word “Graphite” comes from?
The word “graphite” comes from the Greek word (graphein) which means “to write or to draw.” This name was given by the German chemist and mineralogist Abraham Gottlob Werner, in the year 1789.
formation of graphite is considered to most often found as flakes or crystalline
layers in metamorphic rocks such as marble, schist’s and gneisses. Graphite may
also be found in organic-rich shale’s and coal beds. In these cases, the
graphite itself probably resulted from metamorphosis of dead plant and animal
matter. Graphite is also found in veins and sometimes in basalt. Graphite also
occurs in meteorites.
Graphite has many distinctive properties which makes it a very interesting mineral. Graphite is a soft, slippery, grayish-black substance. It has a metallic luster and is opaque to light. It is a good conductor of heat and electricity. Although graphite is a very stable allotrope of carbon but at a very high temperature it can be transformed into artificial diamond. Chemically, graphite is slightly more reactive than diamond.
Varieties of Graphite
We have different types of graphite and they are considered by its quality and its formation. The first type of graphite I am going to present, it’s called “Lump Graphite.” Lump graphite is considered the most valuable, and the highest quality form of natural graphite. It is formed by the direct deposition of solid, graphitic carbon from subterranean, high temperature fluids. Since Lump Graphite has the highest quality, it has a distinct competitive applications.
second and less expensive type of graphite is the Crystalline Flake or the
(Flake Graphite). It occurs as isolated plate-like particles
with hexagonal edges if unbroken and when broken the edges can be irregular or
angular. It has a distinctive plate-like or ‘flake’ formation. Flake graphite is
subdivided into large, medium and fine sizes and is a less common form of
Graphite is formed in metamorphic rocks or calcareous sedimentary rocks. The
grade of flake graphite ranges from 10-12% Cg, and the purity varies from 85-95%
carbon after refining. Natural flake has the widest range of use and accounts
for about 49% of natural graphite consumption.
third type of graphite is the Amorphous Graphite
Amorphous graphite is the most abundant form, but occurs at the lowest in grades
than other natural graphite and is the most abundant. It is formed by the
metamorphism of previously existing anthracite coal seams. The term “amorphous”
refers to its very small crystal size of particles, which are not visible unless
viewed under magnification. Large amorphous graphite deposits are found in
China, Mexico, and the United States.
Synthetic graphite is made by heating high carbon materials, like petroleum coke
and coal tar pitch to temperatures in the range of 2500 to 3000 degrees Celsius.
At these high temperatures, all volatile materials and many metals in the
feedstock are destroyed or driven off. The graphite that remains links into a
sheet-like crystalline structure. Synthetic graphite can have a purity of over
99% carbon, and is used in manufactured products where an extremely pure
material is required.
The major use of graphite is in making lead pencils of different hardness, by mixing it with different proportions of clay. The weakly held layers of carbon atoms in graphite easily slide over each other and are left behind on paper as black marks.
Graphite is used as a dry lubricant in machine parts. Since graphite is a
mineral made of loosely bonded sheets of carbon atoms. Also, it is slippery
texture that makes it a very effective lubricant. Being resistant to
chemicals and having a high melting point and also because it is a good
conductor of heat, graphite is used to make crucibles. The presence of
free electrons makes graphite a good conductor of electricity and it is used to
make electrodes. Graphite has the ability to absorb fast-moving neutrons,
thus, it is used in nuclear reactors to control the speed of the nuclear fission
http://www.nature.com/ngeo/journal/v6/n6/ http://geology.com/minerals/graphite.shtml full/ngeo1827.html