Mudstone is a massive, fine-grained sedimentary rock composed of original clay and silt particles that have been compacted over geological time. Unlike shale, it lacks fissility and breaks into blocky or massive chunks rather than thin layers. In underground coal mines, it frequently forms the immediate roof or floor strata, where it can degrade rapidly upon exposure to moisture and air, causing ground control issues.
Heard on the job
The roof in panel four is mostly weak mudstone, so we need to decrease the bolt spacing to prevent falls.