Description
The mineral graphite is one of the allotropes of carbon. It was
named by Abraham Gottlob Werner in ***9 from the Ancient Greek for
its use in pencils, where it is commonly called lead (not to be
confused with the metallic element lead). Unlike diamond (another
carbon allotrope), graphite is an electrical conductor, a
semimetal. It is, consequently, useful in such applications as arc
lamp electrodes. 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 hard to
ignite. There are three principal types of natural graphite, each
occurring in different types of ore deposit: 1.Crystalline flake
graphite (or flake graphite for short) occurs as isolated, flat,
plate-like particles with hexagonal edges if unbroken and when
broken the edges can be irregular or angular;
2.Amorphous graphite occurs as fine particles and is the result of
thermal metamorphism of coal, the last stage of coalification, and
is sometimes called meta-anthracite. Very fine flake graphite is
sometimes called amorphous in the trade;
3.Lump graphite (also called vein graphite) occurs in fissure veins
or fractures and appears as massive platy intergrowths of fibrous
or acicular crystalline aggregates, and is probably hydrothermal in
origin.
Highly ordered pyrolytic graphite or highly oriented pyrolytic
graphite (HOPG) refers to graphite with an angular spread between
the graphite sheets of less than 1
