Mohs hardness scale

Mohs based the scale on ten readily available minerals. Materials are characterised against the scale by finding the hardest material that they can scratch.

The table below shows comparison with absolute hardness measures by a sclerometer. Mohs' is a purely ordinal scale with, for example, corundum being twice as hard as topaz, but diamond, almost four times as hard as corundum.

Hardness	Mineral	Absolute Hardness
1	Talc (Mg3Si4O10(OH)2)	1
2	Gypsum (CaSO4·2H2O)	3
3	Calcite (CaCO3)	9
4	Fluorite (CaF2)	21
5	Apatite (Ca5(PO4)3(OH-,Cl-,F-))	48
6	Orthoclase (KAlSi3O8)	72
7	Quartz (SiO2)	100
8	Topaz (Al2SiO4(OH-,F-)2)	200
9	Corundum (Al2O3)	400
10	Diamond (C)	1500

The mnemonic traditionally taught to geology students to remember this table is "The Girls Can Flirt And Other Queer Things Can Do."

An alternative table is shown below which has been modified to incorporate additional substances that may fall in between two levels.

Hardness	Mineral
1	Liquid
2	Gypsum
3	Calcite
4	Fluorite
5	Apatite
6	Orthoclase
7	Vitreous pure silica
8	Quartz
9	Topaz
10	Garnet
11	Fused zirconia
12	Fused alumina
13	Silicon carbide
14	Boron carbide
15	Diamond

Referenced By