coal rock type

Coal is a carbon-rich sedimentary rock formed from the hardened remains of ancient plant matter, primarily peat. It is classified by its "rank," which indicates the degree of coalification it has undergone due to burial depth and temperature.123

The progression from peat to coal involves increasing carbon content and decreasing moisture. This process leads to different types of coal, including lignite, subbituminous coal, bituminous coal, and anthracite, with each higher rank generally having a greater heat value.32

Coal can also be classified by its rock type (lithotype) based on its visible components:
* Vitrain: Bright, brittle, and lustrous, formed from woody tissue.
* Clarain: Alternating bright and dull layers with a silky luster.
* Durain: Hard, granular, and dull black to dark gray, formed from resistant plant matter and minerals.
* Fusain: Soft, fibrous, and soot-like, resembling charcoal, likely formed from plant tissue exposed to heat or oxidation.4