Diamond vs Graphite
Diamond and graphite, although they both are identical chemically, yet they show differences between them. They are both composed of carbon, but they are different when it comes to their physical appearance. Hence they may be called polymorphs.
They are called polymorphs because of the fact that they are made of the same chemical but they are different in their physical appearance. Graphite is metallic and opaque whereas diamond is brilliant and transparent.
Both are different in terms of their hardness too. Graphite is considered very soft and has a hardness of only 1 to 2 on the Mohs Hardness Scale. On the other hand diamond is known to be the hardest natural substance. In fact it is said to have a hardness of 10 on the Mohs Hardness Scale. It should be noted that no other substance has the hardness that of a diamond.
Graphite is used as a lubricant and is used as a pencil lead. It is interesting to note that the physical appearance of diamond is due to its natural crystal structure.
One of the important differences between diamond and graphite is the way their molecular arrangement is made. In diamonds, each carbon atom is strongly bonded to four adjacent carbon atoms. Probably this is the reason behind its hardness.
In the case of graphite the individual atoms link up with one another to form sheets of carbon atoms. Within every sheet of carbon atoms, each carbon atom is bonded to three adjacent carbon atoms.
Another important difference between the inner structures of the two substances is that there are no free electrons to wander through the structure in diamond and hence they are said to be great insulators. On the other hand free electrons wander through the structure in graphite. Diamonds are characterized by high index of refraction too.