sand grinding mill three The JOYAL Threering Micro Powder Millultrafine mill is for superfine grinding materials with hardness less than 6 in Moh s scale and humidity less than 6 percent such as kaolin limestone calcite marbletalcum barite gypsum dolomite bentonite mudmica pyrophyllite sepiolite diatomite graphite alunite fluorite potassium feldspar phosphorite pigment and so on}