It is comparable with corundum (a-Al2O3) or sapphire in hardness and can only be polished and finished with abrasives of superior hardness such as cubic boron nitride and diamond, in the form of powder, wheels, and compounds.
Ito ay maihahambing sa corundum (a-Al2O3) o sapiro sa tigas at maaari lamang i-kininis na at natapos na may abrasives ng superior tigas tulad ng kubiko boron nitride at diamante, sa anyo ng mga pulbos, wheels, at compounds.