Identifying a Mineral Using Mohs Hardness Scale

The hardness of a mineral is often used by geologists to help determine the identity of a sample. The Mohs Hardness Scale as developed by a German geologist, Friedrich Mohs, in 1812. The Mohs scale is a relative scale which lists the hardness of 10 common minerals. Talc, #1 on the scale is the softest and diamond, #10, is the hardest. Other common household items have also been assigned to the hardness scale such as glass, fingernail and a penny. The Mohs mineral scale and common objects are:

Hardness	Mineral	Household Item
1	Talc
2	Gypsum
2.5		Fingernail
3	Calcite
3.5		Penny
4	Fluorite
5	Apatite
5.5		Glass / Pocket Knife
6	Orthoclase Feldspar
6.5		Steel File
7	Quartz
8	Topaz
9	Corundum
10	Diamond

How to perform the test: To test the hardness of a mineral, try to scratch the surface of your unknown sample with a mineral or object from the hardness scale listed above. If the unknown sample can not be scratched by the known mineral or object, the hardness of your sample is greater. For example, if your sample was not scratched by fluorite, the hardness of your unknown sample is greater than 4. If your sample was scratched by apatite then you know the hardness of your sample is less than 5. Therefore, the actual hardness of your sample would be between 4 and 5.

Mohs’ Hardness Scale Trivia: The first nine minerals on the Mohs’ Hardness Scale have nearly the same relative hardness between them. For example, fluorite is four times harder than talc, quartz is seven times harder than talc and corundum is nine times harder than talc. However, the tenth mineral on the scale, diamond, is 40 times harder than talc. Talk about your hard gemstones!