What is the chemical formula of a diamond?

The answer is simple: ##"C"##.

Diamond is one form of carbon; the other is graphite. To distinguish them, we write:

• diamond: C(s,diamond)

• graphite: C(s,graphite)

The s stands for solid.

Both diamond and graphite are allotropes of carbon. There are other exotic allotropes of carbon (graphenes and fullerenes among them) but they are much less common.

A diamond consists of a giant three-dimensional network of carbon atoms.

In effect, a diamond is one giant molecule. All we can do is write its empirical formula, which is ##"C"##.