A. Abutment - In coal mining, (1) the weight of the rocks above a narrow roadway is transferred to the solid coal along the sides, which act as abutments of the arch of strata spanning the roadway; and (2) the weight of the rocks over a longwall face is transferred to the front abutment, that is, the solid coal ahead of the face and the back abutment, that is, the settled packs behind the face.
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust.. Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials (as in rock ore), so that pieces of different composition can be differentiated.
Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals, usually those containing metals such as ore containing gold, silver, iron, copper, zinc, nickel, tin and lead, but also involves using the same techniques for excavating ores of gems such as diamonds or rubies.
To make chalk, limestone is first quarried, generally by an open pit quarry method. Next, the limestone must be crushed. Primary crushing, such as in a jaw crusher, breaks down large boulders; secondary crushing pulverizes smaller chunks into pebbles.
Back — The roof or upper part in any underground mining cavity. Backfill — Mine waste or rock used to support the roof after coal removal. Barren — Said of rock or vein material containing no minerals of value, and of strata without coal, or containing coal in seams too thin to be workable.