|1||Talc||Soft||Softest known mineral a fingernail can scratch it so it flakes|
|5||Apatite||5.5||Knife blade, window glass|
|7||Quartz||6.5||Hardened steel file|
|8||Topaz||Can scratch Quartz|
|9||Corundum||Can scratch Topaz|
|10||Diamond||Hardest known mineral. Diamond can scratch all other substances|
Hardness is measured using the MOHS Hardness Scale. A substance's hardness value indicates the resistance to scratching and grades minerals on a relative scale from 1 (which is very soft) to 10 (which is very hard).. In the MOHS scale, a mineral of a given hardness rating will scratch other minerals of the same rating, as well as any minerals of a lower rating. For example, sapphires and rubies have a MOHS rating of 9 and will scratch each other, as well as any mineral with a rating lower than 9. However, they will not scratch diamonds, which are rated 10. The MOHS scale of mineral hardness was devised by the German mineralogist Frederich MOHS (1773-1839) in 1812.