This scale is used to determine the hardness of solids, especially minerals. The following excerpt from an article entitled "How Diamonds Work" by Kevin Bonsor and Candace Gibson, explains.
The entire article may be accessed at: http://science.howstuffworks.com/diamond2.htm.
A diamond ranks a 10 on the Mohs Hardness Scale. The Mohs Scale is used to determine the hardness of solids, especially minerals. It is named after the German mineralogist Friedrich Mohs.
Here's the scale, from softest to hardest:
1. Talc - easily scratched by the fingernail
2. Gypsum - just scratched by the fingernail
3. Calcite - scratches and is scratched by a copper coin
4. Fluorite - not scratched by a copper coin and does not scratch glass
5. Apatite - just scratches glass and is easily scratched by a knife
6. Orthoclase - easily scratches glass and is just scratched by a file
7. Quartz - (amethyst, citrine, tiger's-eye, aventurine) not scratched by a file
8. Topaz - scratched only by corundum and diamond
9. Corundum - (sapphires and rubies) scratched only by a diamond
10. Diamond - scratched only by another diamond
