Glossary term
Mohs scale
A 1–10 scale of relative scratch hardness for minerals.
The Mohs scale ranks minerals by their ability to scratch one another, from talc (1) to diamond (10). Corundum sits at 9. The scale is ordinal, not linear, diamond is many times harder than corundum despite being one step above it. Hardness informs how a gem should be worn and stored.