Corundum vs Ruby
Corundum and Ruby share a composition and differ on 1 measured property — the question a reader asks about any pair of polymorphs.
Corundum vs Ruby
These are different kinds of thing (mineral, mineral variety). Fewer properties mean the same thing across both, so a like-for-like reading may not be available.
Corundum
Al2O3
Aluminium oxide — hardness 9, the mineral of ruby and sapphire, and a major industrial abrasive.
| Property | Corundum | Ruby |
|---|---|---|
| Crystal system Categorical values can be listed side by side but not ordered or subtracted. | trigonal | trigonal |
| Density | 3.95–4.1 g/cm³ higher | 3.97–4.05 g/cm³ |
| Lustre Only one of the two has a figure we can stand behind, so there is nothing to compare. | vitreous to adamantine | Not known |
| Mohs hardness Mohs hardness is an ordinal scale: values can be ranked, but differences and ratios between them are not meaningful. | 9 | 9 |