As coal contains mainly carbon, the conversion of dead vegetation into coal is called carbonization.

Although coal contains only small concentrations of mercury, it is burnt in very large volumes.

Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel.

Since coal and petroleum often contain sulphur compounds, their combustion generates sulfur dioxide.

Some coal contains type II kerogen.

Because the wood is not yet completely transformed into coal, brown coal contains less energy than bituminous coal.

The coal of the Pavlovsky, Skotovsky, and Bikinsky deposits contains germanium and non-ferrous metals.

Unfortunately, coal often contains other chemicals.

Low-rank coals often contain a higher level of moisture content which contains a lower energy content per tonne.

Methane is a relatively pure compound whereas coal contains a significant amount of incombustible ash.