Graphite is a polymorph of the element carbon. diamond
is another polymorph. The two share the same chemistry,
carbon, but have very different structures and very
different properties. Diamond is hardest mineral known
to man, Graphite is one of the softest.
Diamond is an excellent electrical insulator, Graphite
is a good conductor of electricity.
Diamond is the ultimate abrasive, Graphite is a very
Diamond is usually transparent, Graphite is opaque.
Diamond crystallizes in the Isometric system and graphite
crystallizes in the hexagonal system.
Somewhat of a surprise is that at surface temperatures
and pressures, Graphite is the stable form of carbon.
In fact, all diamonds at or near the surface of the
Earth are currently undergoing a transformation into
Graphite. This reaction, fortunately, is extremely slow.
All of the differences between graphite and diamond
are the result of the difference in their respective
structures. Graphite has a sheet like structure where
the atoms all lie in a plane and are only weakly bonded
to the graphite sheets above and below. Diamond has
a framework structure where the carbon atoms are bonded
to other carbon atoms in three dimensions as opposed
to two in graphite. The carbon-carbon bonds in both
minerals are actually quite strong, but it is the application
of those bonds that make the difference. Graphite can
only be confused with the mineral molybdenite which
is metallic bluish silver in color. However, molybdenite
is much denser and has a silver blue streak. Most graphite
is produced through the metamorphism of organic material
in rocks. Even coal is occassionally metamorphosed into
graphite. Some graphite is found in igneous rocks and
also as nodules inside of iron meteorites.