Clastic successions containing coals were commonly developed in deltaic environments with clastic deposits of shales, siltstones, and sandstones, as well as occasional ironstones (typically siderite). The clay mineralogy of the finer-grained rocks is quite variable and can show elevated contents in kaolinite, particularly in paleosols. The logging properties of coals vary according to their rank, but typical figures are:
| Pe | neutron porosity | density porosity (bulk density) | |
| Anthracite | 0.16 | 38 | 72 (1.47) |
| Bituminous | 0.17 | 60 | 86 (1.24) |
| Lignite | 0.20 | 52 | 89 (1.19) |
