Waste rock or stony material associated with coal seams, typically greyish-black, hard, and containing low levels of carbon.

waste rock or mineral found within an ore deposit or coal seam; it contains little carbon and does not burn easily

Rock that contains little or no ore and is thrown away during mining; specifically refers to the non-combustible stony material mixed in with coal. Also written as [[矸石|矸石|gan1 shi2]].