Its drawback there is its tendency to oxidize at contacts, requiring the use of contacts coated with an antioxidant. Aluminum is a very active metal, a fact often disguised by the fact that it rapidly forms barrier oxide layers on exposed surfaces, inhibiting its interaction. When strongly heated it burns rapidly in air, and in the form of a fine dust is explosive. Aluminum oxide, Al2O3, is called alumina and occurs in nature as the mineral corundum. Corundum and impure corundum called emery are used in making abrasive cloths and wheels.
Aluminum sulfate is used in water purification.
It is also used as a mordant in the dying of cloth. A mordant fixes the dye to the cloth, rendering it insoluble. Aluminum has excellent reflective properties and is widely used in evaporated coatings for the manufacture of mirrors. Reference Pauling Ch. Spin Natural Abund.