Friedrich Mohs devised a scale that tested mineral hardness, which means the resistance of a mineral to being scratched. This scale (from 1 to 10) is known as the Mohs Hardness Test. Objects are used as tools to perform the hardness test:
fingernail (hardness = 2,5).
copper penny (hardness = 3)
glass plate or steel knife (hardness = 5,5)
steel file (hardness = 6,5).
According to this scale hardness of the mineral is between 5,5 and 6,5.
