What is the definition of hardness? What is the Hardness Scale? How is it used in mineral testing?

 

Hardness Scale (Friedrich Mohs Scale)

The bonds holding atoms together determine a mineral's

hardness.

In 1812, the Austrian mineralogist Friedrich Mohs devised a

scale of hardness that is still in use today. He selected ten

minerals as standards and arranged them so that any mineral on

 the scale 

would scratch only those below it. Everyday objects can be used 

to test where a mineral fits into the scale. A fingernail has a

hardness of 2.5, and a penknife is 5.5. Minerals of six and above 

will scratch glass; glass will scratch apatite and other minerals 

below it.

Mohs hardness scale 

The Mohs Scale of Hardness Explained