Explanatory notes
… than ordinary aluminium oxide to the action of air and acids, and is very hard. It is used, e.g., as an abrasive, … precious or semi‑precious stones (rubies, sapphires, emeralds, amethysts, aquamarines, etc.), as a dehydrating … the artificial corundum described above and for clarifying liquids; it is mixed with carbon for the manufacture of …