Corundum
Aluminium oxide, the mineral of ruby and sapphire, found as tiny grains in chondrites, some made in other stars.
Key facts
- Formula
- Al2O3
- Family
- Oxides
- Crystal system
- Trigonal
What it is
Corundum is aluminium oxide, hard enough to scratch anything except diamond and a few rare minerals. It is the first major mineral expected to condense from a gas of solar composition as it cools.
Where it is found
Rare corundum grains occur in CAIs in CM and CH chondrites. Some microscopic corundum grains found by dissolving meteorites in acid have oxygen isotopes completely unlike anything in the Solar System: they are presolar grains, formed in the winds of red giant stars and older than the Sun.
How it is recognised
In meteorites it is microscopic and colourless. It is found by its high relief and identified by analysis.
Did you know?
Red corundum is ruby, and blue corundum is sapphire.
Some presolar corundum grains are older than the Solar System by hundreds of millions of years.