Evaluation of the structure of bituminous coal from Sośnica mine in the Upper Silesian Coal Basin (Poland) using reflectance indicating surface (RIS) parameters

The heating leads to the destruction of coal-structure cross-linkages (aliphatic groups or heteroatoms) and various further transformations of the structural net, in addition to the removal of volatile carbonization products. External pressures affect the transformation process, especially by promoting the rearrangement of small structural units to form further elements of anisotropic structure. Thus, in the case of coal from the immediate contact of the intrusion, pressures resulted in values of anisotropy parameters higher than those characterizing coal heated in the laboratory up to 1200 °C, but in the absence of stress. The source of pressure that strongly affected the coal in the mine was probably intrusion related. Weak tectonism in the region of the Sośnica mine could explain the fine biaxial optical character of the low rank parent coals more generally. Pressures associated with thermally evolving gasses conceivably led to the growth of structural anisotropy in the walls of degassing pores. Finally, some structural changes seen in coal adjacent to the intrusion may reflect hydrothermal activity.