21 roller grinding mill is our micro powder grinding mill  ultrafine grinding mill  micro pulverizer  super fine powder grinding mill  which is for super-fine grinding materials with hardness less than 6 in Moh‘s scale and humidity less than 6 percent such as kaolin  limestone  basalt  calcite  marble  talcum  barite  gypsum  dolomite  bentonite mud  mica  pyrophyllite  sepiolite  carbon black  diatomite  graphite  alunite  fluorite  potassium feldspar  phosphorite  pigment  up to 200 kinds