Graphite is one of several molecular
forms (allotropes) of carbon, with others being diamond, fullerenes and amorphous
carbon such as coal
Graphite Hexagonal Crystal Structure
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Graphite has a definite crystal structure which is hexagonal in form. The mineral consists of multiple layers of carbon atoms in a honeycomb pattern. The chemical bonds in the ‘a-b’ plane of the layers is very strong, whereas the ‘c’ bonds holding the layers together are weak. This is the reason for the peculiar properties of graphite, such as lubricity (where the layers slide over each other) and high electrical and thermal conductivity (due to the mobile electron clouds of each ‘a-b’ layer). A single layer is referred to as ‘graphene,’ a 2-dimensional structure with virtually no thickness. |
| Fullerenes and Nanotubes are not crystalline, but are like a layer of graphene in the form of a ball or tube. |
Fullerenes and Nanotube Structures
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Diamond has a definite crystal structure which is
tetrahedral in form. The mineral has no layering of carbon atoms. The chemical bonds
are all very strong in all directions, giving rise to its extreme hardness.
Diamond Tetrahedral Crystal Structure |
 Coal Non-Crystalline, Amorphous Structure
Coal has no crystal structure and this is referred to as
amorphous (not to be confused with amorphous graphite). Another example is wood char and
other burnt organic substances.
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