During the early 1800s, a German mineralogist named Friedrich
Mohs devised a scale that tested mineral hardness, which means the
resistance of a mineral to being scratched. This scale, which ran from
1 to 10, was named after Mohs, and is known as the Mohs Hardness Test.
(Hardness should not be confused with brittleness. Diamond, the hardest
known natural substance, can produce a scratch on virtually all other substances,
but can easily be shattered by the blow of a hammer.) Keep in mind that
the Mohs scale does not indicate exact hardness, which depends upon the
purity of the mineral sample and its degree of crystallinity. The Mohs
Scale is shown below, using commonly known minerals to represent each degree
While a reference set of the above minerals may be used to test the hardness
of an unknown mineral, such a set is rarely used in actual practice; particularly
because diamond is rather expensive to be used as an abrasive. Instead,
common 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)
Using the above testing tools, you should be able to determine the Mohs
Hardness of an unknown mineral to the nearest half number on the scale.
Keep these principles in mind when performing the hardness test:
"That which scratches is harder than that which
has been scratched."
"Objects of equal hardness can be scratched with difficulty."