Mohs scale of mineral hardness

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The Mohs scale of mineral hardness (or simply Mohs scale) is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material.

General

The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. The samples of matter used by Mohs are all different minerals. Minerals are pure substances found in nature.

The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is four times as hard as corundum.

Minerals

Classical scale

Mohs hardness Mineral Chemical formula Image
1 Talc Mg3Si4O10(OH)2
2 Gypsum CaSO4·2H2O
3 Calcite CaCO3
4 Fluorite CaF2
5 Apatite Ca5(PO4)3(OH,Cl,F)
6 Orthoclase feldspar KAlSi3O8
7 Quartz SiO2
8 Topaz Al2SiO4(OH,F)2
9 Corundum Al2O3
10 Diamond C

Intermediate scale

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[1]
2 hexagonal boron nitride,[2] 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),[3] stishovite, titanium diboride
10 diamond, carbonado
>11 nanocrystalline diamond (hyperdiamond, ultrahard fullerite), rhenium diboride (c-axis)[3]

References

  1. "Ice is a mineral" in Exploring Ice in the Solar System. messenger-education.org
  2. Berger, Lev I. (1996). Semiconductor Materials (First ed.). Boca Raton, FL: CRC Press. p. 126. ISBN 978-0849389122. 
  3. 3.0 3.1 Levine, Jonathan B.; Tolbert, Sarah H.; Kaner, Richard B. (2009). "Advancements in the Search for Superhard Ultra-Incompressible Metal Borides" (PDF). Advanced Functional Materials. pp. 3526–3527. doi:10.1002/adfm.200901257. 

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