Coal is made up of carbon. It is an allotrope of carbon. Coal also contains arenes or aromatic hydrocarbons like benzene, toluene, xylene, naphthalene and anthracene.

Petroleum is a mixture of hydrocarbons (containing C and H). 

There are mainly three classifications of coal: Anthracite, Bituminous and Lignite. Lignite has the lowest grade of coal whereas anthracite is the highest one. Power plants generally use steam coal which is a grade between anthracite and bituminous.