Carbonization or carbonisation is the term for the conversion of an organic substance(like plants and dead animal residue) into carbon through pyrolysis or destructive distillation. It is often used in organic chemistry with reference to the generation of coal gas and coal tar from raw coal. Fossil fuels in general are the products of the carbonization of vegetable matter.
This process occurs at a faster rate.
Coalification is the process of the chemical transformation from vegetation into coal (i.e. the transformation of the complex biological and molecular structures in the cells of plants into the chemical fragments and structures seen in coal).
This process occurs at a very slow rate.