Mohs scale of mineral hardness

qualitative ordinal scale characterizing scratch resistance of various minerals
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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 minerReadals. 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 corundum (at 9 on the scale).[3] The Mohs scale may not be perfect, but field geologists still find it very useful.

Mohs hardness Mineral Chemical formula Absolute hardness[4] 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

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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
[5]

References

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

Other websites

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