This geological feature is a distinct, narrow band of tough rock, often sandstone or ironstone, that interrupts a thicker sequence of softer shales or coal measures. In underground mining, encountering one can complicate drilling and blasting because its hardness differs sharply from the surrounding rock. Roof bolters must often anchor their bolts above these bands to ensure a stable hanging wall.
Heard on the job
The shearer is going to struggle on this panel because there's a heavy sandstone girdle running right through the middle of the seam.