Formation and distribution of coal balls in the Herrin Coal ...
Large areas of concentrated coal balls (permineralized peat) up to 4 m thick obstructed longwall mining in the Herrin Coal at the Old Ben No. 24 mine. The largest coal‐ball area mapped contained >1500 m 3; several areas contained >400 m 3 of coal balls. In‐mine mapping established that there were two types of roof (freshwater and marine ...