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Mohs Scale of Mineral Hardness

 

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Mohs Scale Designed to Measure Hardness not Toughness

 

Mohs scale of mineral hardness was created in 1812 by Friedrich Mohs, a mineralogist from Vienna. Its purpose was to identify 'scratch hardness' which is the resistance of one mineral when being scratched by another. It's important to note that a mineral's hardness should not be confused for toughness

Mohs scale was made up of ten common minerals all of which had a different level of hardness.  The softest was the clay mineral talc and the hardest was diamond. Still referred to today as Mohs scale of mineral hardness, it's widely used and demonstrates that talc which grades 1 on the scale can be scratched by gypsum which is grade 2. Gypsum in turn can be scratched by calcite because calcite is harder than gypsum hence calcite is graded as 3. The harder the mineral the higher the grade and with diamond being the hardest of all minerals it's grade is 10.

Every mineral on the Mohs scale of mineral hardness can scratch another that has a lower grade and can in turn be scratched by one that's higher. Minerals of the same hardness can scratch each other.  Half grades are also used and almost all known minerals now have a place on the scale.

It's important to understand however that scratch resistance is not the same as toughness.  Diamond for example is the hardest of all minerals yet is brittle so if caught at the right angle will chip or shatter quite easily.  Mohs scale of mineral hardness describes the resistance of one mineral to be scratched by another, it doesn't describe a mineral's resistance to chipping or breaking.  

 

Hardness

Mineral

Examples

1

Talc

Talcum powder

2

Gypsum

Selenite

3

Calcite

Calcite

4

Fluorite

Fluorite

5

Apatite

Another example is Turquoise

6

Orthoclase, Feldspar

Labradorite, Moonstone, Sunstone, Unakite  Amazonite

7

Quartz

Amethyst, Citrine, Rose Quartz

8

Topaz

Topaz

9

Corundum

Sapphire, Ruby

10

Diamond

The hardest of all natural minerals

 

 

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