Moh's Scale of Hardness
| 1 | Talc |
| 2 | Gypsum |
| 3 | Calcite |
| 4 | Fluorite |
| 5 | Apatite |
| 6 | Feldspar |
| 7 |
Quartz
|
| 8 | Topaz |
| 9 | Corundum |
| 10 | Diamond |
Talc and Gypsum are very soft and can be scratched by a finger nail. Calcite and Fluorite are easily scratched by a knife-blade. Apatite is scratched by a knife-blade with some difficulty. Feldspar is barely scratched by a knife-blade, but easily scratched by a steel file. Minerals with the hardness of Quartz and higher will scratch glass, but are not scratched by a steel file.
Diamond, at a hardness of 10, does not mean that Diamond is only 10 times harder than Talc. It means that it is harder than the other nine minerals on Moh's scale. Diamond is actually fifty times harder than Talc.
- Melita Scheffel