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ALUMINUM OXIDE [uh-loo-muh-nuhm aak-side]
What it is: A white abrasive used on files that can be less aggressive on the nail surface than the same grit of other materials.
(NB: In its crystalline phase, as the mineral corundum, varieties form the gem stones ruby & sapphire. Corundum is the most common naturally occurring crystalline form of aluminum oxide.)Â