Mohs scale of mineral hardness

The mohs scale, named after Friedrich Mohs

Mohs' scale of mineral hardness is named after Friedrich Mohs, a mineralogist. Mohs scale is ordered by hardness, determined by which minerals can scratch other minerals.

Rocks are made up of one or more minerals. According to the scale, Talc is the softest: it can be scratched by all other materials. Gypsum is harder: it can scratch talc but not calcite, which is even harder. The hardness of a mineral is mainly controlled by the strength of the bonding between the atoms and partly by the size of the atoms. It is a measure of the resistance of the mineral to scratching, the Mohs scale is for natural minerals. For manufactured products other measures of hardness are better.

Diamond is always at the top of the scale, being the hardest mineral. There are ten minerals in Mohs scale, talc, gypsum, calcite, fluorite, apatite, feldspar, quartz, topaz, corundum, and for last and hardest, diamond. Because the Mohs scale was made long ago, it is not exactly correct – for example, several minerals are now known to be harder than corundum (at 9 on the scale). The Mohs scale may not be perfect, but field geologists still find it very useful.

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

Relative hardness of some items

2.5 Fingernail
2.5–3 Gold, Silver
3 Copper penny
4–4.5 Platinum
4–5 Iron
5.5 Knife blade
6.5 Iron pyrite
5.5 Glass
6.5 Hardened steel file

Other websites

• http://www.mineraltown.com/infocoleccionar/mohs_scale_of_hardness.htm
• How to use the Mohs scale of mineral hardness Archived 2006-12-30 at the Wayback Machine