Aluminium oxide

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**Properties**
General
Name	Aluminium oxide Aluminum oxide (US)
Chemical Formula	Al₂O₃
Appearance	White crystalline powder or solid
Physical
Formula weight	101.96 amu
Melting point at SP	2303 K
Boiling point at SP	3250 K
Density	3.97 × 10³ kg/m³
Crystal structure	Trigonal (hex)
Solubility	Insoluble
Thermochemistry
Δ_fH⁰_liquid	−1620.57 kJ/mol
Δ_fH⁰_solid	−1675.69 kJ/mol
S⁰_{liquid, 1 bar}	67.24 J/mol·K
S⁰_solid	50.9 J/mol·K
Safety
Injestion	Low hazard
Inhalation	May cause irritation or lung damage
Skin	Low hazard
Eyes	Low hazard
SI units were used where possible.

Aluminium oxide (or aluminum oxide) (Al₂O₃) is a chemical compound of aluminium and oxygen. It can also be called alumina, a formally obsolete name still frequently used in the mining industry.

Aluminium oxide is the main component of the principal ore of aluminium (bauxite), and the main component of the gems ruby and sapphire.

Aluminium oxide is responsible for metallic aluminium's resistance to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin layer of aluminium oxide quickly forms on any exposed aluminium surface. This layer protects the metal from further oxidation.

Powdered aluminium oxide is frequently used as a medium for chromatography.

Aluminium oxide was taken off the EPA's chemicals lists in 1988.