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The Mohs Scale of Hardness

This scale used for measuring the "hardness" of minerals is described by Wikipedia as:

"a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material."

This hardness scale is a simple scale based on the ability of one mineral to to scratch another mineral visibly. By using this method of testing a mineral's hardness, identifications of various mineral hardnesses can be determined. On the Mohs scale of mineral hardness, Talc is at the "soft" end of the scale with Diamond at the hard end.

Mohs Hardness Scale Reference Table

Mineral Hardness Note
Talc 1 Talc is a mineral that is the primary part of talcum powder.
Gypsum 2 Formed when seawater evaporates from the surface of the Earth. It is also found in drywall.
Calcite 3 A carbonate mineral found in many popular stones such as marble and limestone. It is often the primary constituent of the shells of marine organisms.
Fluorite 4 The mineral form of calcium fluoride. It is often used for ornamental carvings.
Apatite 5 A group of phosphate minerals named by the German geologist Abraham Gottlob Werner.
Feldspar 6 Feldspars are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight.
Quartz 7 A hard, crystalline mineral composed of silicon and oxygen atoms which belongs to the trigonal crystal system.
Topaz 8 Topaz is a silicate mineral of aluminium and fluorine. In its natural state, Topaz is golden brown to yellow in color.
Corundum 9 Corundum occurs as a mineral in mica schist, gneiss, and some marbles in metamorphic terranes.
Diamond 10 Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic.

The above hardness scale is used and referred to often when discussing various stone composition in written articles and references.