ZYM Ultrafine Powder Mill Grinding. The JOYAL Threering Micro Powder Mill(ultrafine 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, marble,talcum, barite, gypsum, dolomite, bentonite mud,mica, pyrophyllite, sepiolite, diatomite, graphite, alunite, fluorite, potassium feldspar ...