Linked from
The 11 pages that link to Corundum, each with the reason it gives.
Mohs scaleBroader topic: It sits just below diamond among the scale’s reference minerals.
AluminaBroader topic: This stable crystal structure underlies many dense alumina ceramics.
Aluminium oxideBroader topic: This structure is the basis of aluminium oxide's exceptional hardness.
SapphireNarrower topic: Sapphire is the gem variety of corundum, distinguished mainly by color.
SpinelCompared with: Corundum is harder than spinel and has a distinct crystal structure.