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Earth and Space > Mohs Hardness Testing

Hardness is a property of a material which enables it to resist plastic deformation, cutting, scratching, abrasion or bending.

There are many hardness tests used in manufacturing and product design but the most commonly used hardness test used by geologists and in schools is the Mohs hardness test.

The test was developed in 1822 by a German mineralogist to compare the relative hardness or scratch resistance of minerals. He took ten well known minerals and arranged them in order of 'scratch hardness' The idea is that if a mineral specimen being tested can be scratched by a mineral in the list then it is softer than that mineral. If in turn it can scratch another mineral it is harder than that mineral. As such the table is not to scale in terms of hardness being proportional, it is just really an ordered list of relative hardness.

The Mohs hardness test was developed to be a crude but effective in field tests by mineralogists. It has been used in schools and colleges for many years to determine the relative hardness of the ten listed minerals.

The Mohs hardness scale table is shown below:

Mineral Hardness Scale
Diamond 10
Corundum 9
Topaz 8
Quartz 7
Orthoclase (Feldspar) 6
Apatite 5
Fluorite 4
Calcite 3
Gypsum 2
Talc 1