Mohs scale of mineral hardness

Jump to: navigation, search


The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science. Mohs based the scale on ten minerals that are all readily available. As the hardest known naturally occurring substance, diamond is at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5.

The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is almost four times as hard as corundum. The table below shows comparison with absolute hardness measured by a sclerometer.

Hardness Mineral Absolute Hardness
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 Orthoclase Feldspar (KAlSi3O8) 72
7 Quartz (SiO2) 100
8 Topaz (Al2SiO4(OH-,F-)2) 200
9 Corundum (Al2O3) 400
10 Diamond (C) 1500


On the Mohs scale, a pencil lead has a hardness of 1; a fingernail has hardness 2.5; a copper penny, about 3.5; a knife blade, 5.5; window glass, 5.5; steel file, 6.5.[1] Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale.

The table below incorporates additional substances that may fall between levels:

Hardness Substance or Mineral
1 Talc
2 Gypsum
2.5 to 3 pure Gold, Silver, Aluminum
3 Calcite, Copper penny
4 Fluorite
4 to 4.5 Platinum
4 to 5 Iron
5 Apatite
6 Orthoclase
6 Titanium
6.5 Iron pyrite
6 to 7 Glass, Vitreous pure silica
7 Quartz
7 to 7.5 Garnet
7 to 8 Hardened steel
8 Topaz
9 Corundum
9 to 9.5 Carborundum
10 Diamond
>10 Ultrahard Fullerite
>10 Aggregated diamond nanorods


References

ar:مقياس موس bg:Скала на Моос ca:Duresa Mohs cs:Mohsova stupnice tvrdosti de:Härte#H.C3.A4rtepr.C3.BCfung_nach_Mohs et:Mohsi astmikeo:Mohs-skalohr:Mohsova skala ko:모스 굳기계 id:Skala Mohs is:Mohs kvarði it:Scala di Mohs he:סולם מוס lv:Mosa skala lt:Moso skalė hu:Mohs-féle keménységi skála nl:Hardheidsschaal van Mohsno:Mohs skala nn:Mohs hardleiksskala mn:Моссын шатлал nds:Mohshardsk:Mohsova stupnica tvrdosti sl:Mohsova trdotna lestvica sr:Тврдоћа по Мосовој скали sh:Tvrdoća po Mosovoj skali sv:Mohs hårdhetsskala th:สเกลของโมส์uk:Шкала Мооса


Linked-in.jpg