The are ten minerals that form an arbitrary hardness scale to which others are compared. They are:

1. talc
2. gypsum, CaSO₄ ^. 2H₂O
3. calcite, CaCO₃
4. fluorite, CaF₂
5. apatite
6. orthoclase or potassium feldspar, KAlSi₃O₈
7. quartz, SiO₂
8. topaz
9. corundum, Al₂O₃
10. diamond, C