Impact Crusher The 8 x coarse size fraction (203,200x34,925 µm), considered of medium hardness (about kwh/t), is submitted to crushing in an impact crusher to liberate, at the coarser size fraction possible, the impure phosphate fluor or hydroxyapatite from coarse dolomite and other impurities, such as aluminum silies, clays, quartz, and iron bearing minerals.