Morphology, formation and palaeo-environmental implications of naturally formed char particles in coals and carbonaceous mudstones

Combustion char morphotypes are derived from pulverised fuel combustion of coal. Microscopic examination of polished blocks of Carboniferous, Permian and Jurassic coals and carbonaceous mudstones has, however, also revealed the occurrence of particles with typical char morphology in these deposits. The particles are whiter than the associated huminite/vitrinite and should be considered to belong to the inertinite maceral group, but in both morphology and derivation they do not correspond to any of the established inertinite macerals. Thus, these morphotypes are considered to represent naturally formed char. They are generally of the dense crassinetwork/ mixed network/mixed and inertoid char morphotypes. Low temperature combustion of coal, particularly in a muffle furnace, yields similar char morphotypes, hinting that the naturally formed chars were derived by low temperature burning of gelified organic matter. This may have been during surface/ground fires in peat mires. Thus, despite their minor importance volumetrically, the naturally formed chars may have palaeo-environmetal implications, particularly if additional evidence is provided by pyroinertinite and/or pyrolytic carbon.