1.An extremely hard mineral, aluminum oxide, Al2O3, sometimes containing iron, magnesia, or silica, that occurs in gem varieties such as ruby and sapphire and in a common black, brown, or blue form used chiefly in abrasives.
2.The result shows that the formula (NR 50phr, BR 30phr, Gutta-Percha 20phr, stearic acid 5phr, magnesia 2phr, zinc oxide 2phr, antioxidant D 1phr, high abrasion fine furnace black 50phr, aromatic oil 5phr, sulfur 2phr, accelerant DM 2phr) is the most excellent.
