Mohs Scale of Hardness:

1. Talc (easily scratched by a fingernail; feels soft and greasy)
2. Gypsum (just scratched by the fingernail; not greasy or soft)
3. Calcite (very easily scratched by a knife, just scratched by a sharp edge of copper, such as that of a new penny)
4. Fluorite (easily scratched by a knife, but not hard enough to scratch glass)
5. Apatite (scratched by a knife, but just scratches ordinary glass)
6. Orthoclase (not scratched by a knife and scratches window or bottle glass easily)
7. Quartz (scratches both a knife and hard glass easily; harder than any other common substance)
8. Topaz (scratches quartz easily and much harder than any common substance)
9. Corundum (scratches topaz and compares with the manufactured product called carborundum, though it is very different chemically)
10. Diamond (scratches topaz and corundum easily; is the hardest substance known)

Minerals of the same hardness can scratch each other.

Minerals that fall between any numbered mineral are given a half numeral. For example, pyrite measures 6.5, beryl 7.5, and the fingernail is 2.5.