Mohs scale of mineral hardness
Mohs scale of mineral hardness is named after the scientist, Friedrich Mohs, who invented a scale of hardness based on the ability of one mineral to scratch another. Rocks are made up of one or more minerals. According to the scale, Talc is the softest: it can be scratched by all other materials. Gypsum is harder: it can scratch talc but not calcite, which is even harder. The hardness of a mineral is mainly controlled by the strength of the bonding between the atoms and partly by the size of the atoms. It is a measure of the resistance of the mineral to scratching.
The hardest mineral [change]
As it says in Mohs scale, the diamond is always at the most top of the scale, being the hardest mineral. There are ten minerals in Mohs scale, talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, and for last and the hardest, diamond. But since the Mohs scale was made long ago, it is not exactly correct - for example, many have found and reported minerals higher in hardness than the diamond. So the Mohs scale may not be most completely perfect, but it is still quite trustworthy.
Hardness of some other items [change]
2.5–3 Gold, Silver
3 Copper penny
5.5 Knife blade
6.5 Iron pyrite
7+ Hardened steel file
Other websites [change]
- How to use the Mohs scale of mineral hardness 
- Mohs scale of Hardness, http://www.amfed.org/t_mohs.htm