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Mohs Hardness Scale

Open wooden box collection containing ten compartments, each holding a numbered mineral specimen.
Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale

The Mohs scale of mineral hardness is an ordinal scale measuring the hardness of minerals through the abilities of harder materials able to scratch softer materials. Invented by Icons-flag-de.png German mineralogist Friedrich Mohs in 1812, it is one of various definitions of hardness in material science.[1]

Mohs hardness Mineral Chemical formula Absolute hardness[2] Image
1 Talc Mg3Si4O10(OH)2 1 Talc block.jpg
2 Gypsum CaSO4·2H2O 3 Gypse Arignac.jpg
3 Calcite CaCO3 9 Calcite-sample2.jpg
4 Fluorite CaF2 21 Fluorite with Iron Pyrite.jpg
5 Apatite Ca5(PO4)3(OH,Cl,F) 48 Apatite Canada.jpg
6 Orthoclase feldspar KAlSi3O8 72 OrthoclaseBresil.jpg
7 Quartz SiO2 100 Quartz Brésil.jpg
8 Topaz Al2SiO4(OH,F)2 200 Topaz cut.jpg
9 Corundum Al2O3 400 Cut Ruby.jpg
10 Diamond C 1500 Rough diamond.jpg
Hardness Substance or mineral
0.2–0.3 caesium, rubidium
0.5–0.6 lithium, sodium, potassium
1 talc
1.5 gallium, strontium, indium, tin, barium, thallium, lead, graphite, ice[3]
2 hexagonal boron nitride,[4] calcium, selenium, cadmium, sulfur, tellurium, bismuth, gypsum
2–2.5 halite (rock salt)
2.5–3 gold, silver, aluminium, zinc, lanthanum, cerium, Jet (lignite)
3 calcite, copper, arsenic, antimony, thorium, dentin
3.5 platinum
4 fluorite, iron, nickel
4–4.5 steel
5 apatite (tooth enamel), zirconium, palladium, obsidian (volcanic glass)
5.5 beryllium, molybdenum, hafnium, glass, cobalt
6 orthoclase, titanium, manganese, germanium, niobium, rhodium, uranium
6–7 fused quartz, iron pyrite, silicon, ruthenium, iridium, tantalum, opal, peridot, tanzanite, jade
7 osmium, quartz, rhenium, vanadium
7.5–8 emerald, hardened steel, tungsten, spinel
8 topaz, cubic zirconia
8.5 chrysoberyl, chromium, silicon nitride, tantalum carbide
9 corundum, tungsten carbide, titanium nitride
9–9.5 silicon carbide (carborundum), titanium carbide
9.5–10 boron, boron nitride, rhenium diboride (a-axis),[5] stishovite, titanium diboride
10 diamond, carbonado
>11 nanocrystalline diamond (hyperdiamond, ultrahard fullerite), rhenium diboride (c-axis)[5]

Comparison with Vickers scaleEdit

This is a comparison between Mohs's scale and the similar Vicker's scale.

Mineral
name
Hardness (Mohs) Hardness (Vickers)
kg/mm2
Graphite 1–2 VHN10=7–11
Tin VHN10=7–9
Bismuth 2–2½ VHN100=16–18
Gold VHN10=30–34
Silver VHN100=61–65
Chalcocite 2½–3 VHN100=84–87
Copper 2½–3 VHN100=77–99
Galena VHN100=79–104
Sphalerite 3½–4 VHN100=208–224
Heazlewoodite 4 VHN100=230–254
Carrollite 4½–5½ VHN100=507–586
Goethite 5–5½ VHN100=667
Hematite 5–6 VHN100=1,000–1,100
Chromite VHN100=1,278–1,456
Anatase 5½–6 VHN100=616–698
Rutile 6–6½ VHN100=894–974
Pyrite 6–6½ VHN100=1,505–1,520
Bowieite 7 VHN100=858–1,288
Euclase VHN100=1,310
Chromium VHN100=1,875–2,000

ReferencesEdit

  1. "Mohs hardness" in Encyclopædia Britannica Online
  2. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  3. "Ice is a mineral" in Exploring Ice in the Solar System. messenger-education.org
  4. Lua error in Module:Citation/CS1 at line 925: attempt to concatenate local 'str' (a table value).
  5. 5.0 5.1 Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).


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