Coal is a hard rock which can be burned as a solid fossil fuel. It is mostly carbon but also contains hydrogen, sulphur, oxygen and nitrogen. It is a sedimentary rock formed from peat, by the pressure of rocks laid down later on top.
Peat, and therefore coal, is formed from the remains of plants which lived millions of years ago in tropical wetlands, such as those of the late Carboniferous period (the Pennsylvanian). Also wood heated in an airless space can make charcoal, which is like coal.
