The hardness of a mineral is a way of describing how easy or difficult it is to scratch the mineral. It is used, in combination with the other physical properties, to help identify a mineral specimen.
In mineral books, hardness is shown using the letter “H.” An example of this is “Talc, H1”.
Mineralogists realized that a way to measure the hardness of minerals was needed. In 1824, a mineralogist from Austria named Friederich Mohs chose 10 common minerals and arranged them in order from softest to hardest. This is called the Mohs Scale of Hardness and today is used by mineralogists all over the world.
The Mohs Scale of Hardness:
6. Orthoclase Feldspar