Carborundum, also known as Silicon Carbide (SiC), is widely used as an abrasive primarily because it is extremely hard. Abrasive materials work by scratching or grinding away the surface of other materials, a process that requires the abrasive to be harder than the material being abraded. Carborundum is one of the hardest known materials, ranking high on the Mohs scale of hardness (around 9-9.5), making it effective for grinding and cutting hard substances.