The hardness scale, or the Mohs Hardness Scale, was developed by Friedrich Mohs, a German geologist and mineralogist, in 1812. This qualitative test was the first widely used field test among geologists.
The Mohs Hardness Scale ranges from one to 10, where one is the softest and 10 is the hardest. For example, talc is rated one, while diamonds are rated 10.
Typically, the test requires the use of a porcelain streak plate and an unidentified specimen. An experimenter scratches the mineral onto the streak plate and makes observations based on how the mineral reacts to the friction. If the mineral breaks down, it has a lower number on the hardness scale. If the mineral scratches the plate itself, the number is higher.