Properties of Corundum

Corundum is a crystalline form of aluminum oxide (Al2O3) and is one of the hardest minerals known. It is commonly recognized for its exceptional hardness and durability.

Image of corundum mineral
Credit: Rob Lavinsky, iRocks.com - CC-BY-SA-3.0, via Wikimedia Commons

The following table provides a comprehensive list of corundum properties in both SI and US customary/Imperial units at normal temperature and pressure (NTP).

Note: click on the icon to switch between Metric and Imperial units.

Table of Corundum Properties
Physical Properties
Metric
Chemical FormulaAl2O3
Molar Mass101.96 g/mol
Crystal SystemTrigonal (rhombohedral)
Mohs Hardness9
Density3980 - 4020 kg/m3
ColorColorless, yellow, red, blue green, violet, black
DiaphaneityTransparent to opaque
LusterVitreous to adamantine
CleavageNone
FractureUneven
StreakWhite
Thermal PropertiesMetric
Melting Point2054 °C

Note: unless stated otherwise, all values are taken at room temperature (approximately 20°C or 68°F) and 1 atm pressure. (1 atm = 101,325 Pa)

Related Pages
References: 1) Cardarelli, François. Materials Handbook: A Concise Desktop Reference. Switzerland: Springer International Publishing, 2018. 2) CRC Handbook of Chemistry and Physics, 97th Edition. United Kingdom: CRC Press, 2016-2017.