Diamond and cubic boron nitride (CBN) are the hardest known abrasives and for this reason are also frequently known as "superabrasives". Consequently they are suitable for processing those materials which are difficult, if not impossible, to work using conventional abrasives such as silicon carbide or corundum.

Diamond and CBN have the same crystalline structure, diamond consisting of pure carbon and CBN being a compound of boron and nitrogen.

Hardness comparison of various materials