Mohs Scale of Hardness

Mohs Scale of Mineral Hardness

In 1812 the Mohs scale of mineral hardness was devised by the German mineralogist Frederich Mohs (1773-1839), who selected the ten minerals because they were common or readily available. The scale is not a linear scale, but somewhat arbitrary.

Hardness	Mineral	Associations and Uses
1	Talc	Talcum powder.
2	Gypsum	Plaster of paris. Gypsum is formed when seawater evaporates from the Earth’s surface.
3	Calcite	Limestone and most shells contain calcite.
4	Fluorite	Fluorine from fluorite prevents tooth decay.
5	Apatite	Apatite is a mineral in vertebrate bones and teeth.
6	Orthoclase	Orthoclase is a feldspar, and in German, "feld" means "field".
7	Quartz	Quartz is the most common mineral in the Earth's crust.
8	Topaz	The November birthstone. Emerald and aquamarine are varieties of beryl with a hardness of 8.
9	Corundum	Sapphire and ruby are varieties of corundum. Twice as hard as topaz.
10	Diamond	Used in jewelry and cutting tools. Four times as hard as corundum.

Hardness of some other items:

2.5	Fingernail
2.5–3	Gold, Silver
3	Copper penny
4-4.5	Platinum
4-5	Iron
5.5	Knife blade
6-7	Glass
6.5	Iron pyrite
7+	Hardened steel file
>10	Wurtzite Boron Nitride
>10	Lonsdaleite (Hexagonal Diamond)

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