Coal is basic fuel that appears in large veins in starting area and in Igneous Biome. It is being used primary to generate energy using Coal Generators.

Small coal vein

Coal is a renewable resource, as long as there Hatches on map - those resource-devouring night creatures yield 125 kg of Coal each time they extrete waste (at night, if they managed to find something to eat). Hatches can be found burrowed or as a "Burried object".