A naturally occurring material, Alumina comes in either the alpha (hard at 2000 HV, mohs 9) or the gamma (soft at mohs 9) phase. The Alumna abrasive is mainly used for final polishing due to its durability and hardness. Unlike SIC abrasive, alumna is easier to break down into colloidal or submicron particles.

It is worth noting that bigger coated or bonded grit alumina sizes are available commercially. But, they are not recommended for metallurgic uses because they turn dull. This results to a lower cut rate and a higher subsurface and surface damage.