Mohs scale of mineral hardness

qualitative ordinal scale characterizing scratch resistance of various minerals

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.[1]

An example of the Mohs scale
The mohs scale, named after Friedrich Mohs

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.[2]

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 the diamond.[source?] The Mohs scale may not be perfect, but field geologists still find it very useful.

Mohs hardnessMineralChemical formulaAbsolute hardness[3]Image
1Talc
Mg3Si4O10(OH)2
1Talc block.jpg
2Gypsum
CaSO4·2H2O
2Gypse Arignac.jpg
3CalciteCaCO39Calcite-sample2.jpg
4FluoriteCaF221Fluorite with Iron Pyrite.jpg
5ApatiteCa5(PO4)3(OH,Cl,F)48Apatite Canada.jpg
6FeldsparKAlSi3O872OrthoclaseBresil.jpg
7QuartzSiO2100Quartz Brésil.jpg
8TopazAl2SiO4(OH,F)2200Topaz cut.jpg
9CorundumAl2O3400Cut Ruby.jpg
10DiamondC1500Rough diamond.jpg

Relative hardness of some items

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

References

  1. "Mohs Hardness Scale: Testing the Resistance to Being Scratched". geology.com. Retrieved 2020-03-09.
  2. NDT Resource Center: hardness. [1]
  3. Applied Mineralogy: applications in industry and environment. Swapna Mukherjee 2011 [2]
  4. Mohs scale of Hardness, http://www.amfed.org/t_mohs.htm

Other websites