Emery, EHM uhr ee or EHM ree, is a hard black or gray rock that consists chiefly of the minerals corundum, magnetite, and, in some cases, spinel. Its hardness depends on the amount of corundum. People use emery as an abrasive (grinding and polishing material). When used for grinding, emery is crushed into small grains and glued onto cloth or paper. The grains may be mixed with clay to produce grinding wheels. For use in polishing, emery is reduced to a fine powder. Certain other substances are gradually replacing emery as an abrasive. In the United States, the major use of emery is to give traction to stairs and pavement.