Mohs scale of mineral hardness

  1. Pages with script errors
  2. Pages with broken file links
  3. Materials science
  4. Mineralogy
  5. Hardness tests


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 geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science.[1] The method of comparing hardness by seeing which minerals can scratch others, however, is of great antiquity, having first been mentioned by Theophrastus in his treatise On Stones, circa 300 BC, followed by Pliny the Elder in his Naturalis Historia, circa 77 AD.[2][3][4]

Minerals

The Mohs scale of mineral hardness is based on the ability of one natural sample of matter to scratch another. The samples of matter used by Mohs are all minerals. Minerals are pure substances found in nature. Rocks are made up of one or more minerals.[5] As the hardest known naturally occurring substance when the scale was designed, diamonds are 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.[6]

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. The table below shows comparison with absolute hardness measured by a sclerometer, with pictorial examples.[7][8]

Mohs hardness Mineral Chemical formula Absolute hardness Image
1 Talc Mg3Si4O10(OH)2 1 100px
2 Gypsum CaSO4·2H2O 3 100px
3 Calcite CaCO3 9 100px
4 Fluorite CaF2 21 100px
5 Apatite Ca5(PO4)3(OH–,Cl–,F–) 48 100px
6 Orthoclase Feldspar KAlSi3O8 72 100px
7 Quartz SiO2 100 100px
8 Topaz Al2SiO4(OH–,F–)2 200 100px
9 Corundum Al2O3 400 100px
10 Diamond C 1600 100px

On the Mohs scale, graphite (a principal constituent of pencil "lead") has a hardness of 1.5; a fingernail, 2.2–2.5; a copper penny, 3.2–3.5; a pocketknife 5.1; a knife blade, 5.5; window glass plate, 5.5; and a steel file, 6.5.[9] A streak plate (unglazed porcelain) has a hardness of 7.0. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale.[1]

Intermediate hardness

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

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
2 hexagonal boron nitride,[10] calcium, selenium, cadmium, sulfur, tellurium, bismuth
2.5 to 3 magnesium, gold, silver, aluminium, zinc, lanthanum, cerium, Jet_(lignite) (lignite)
3 calcite, copper, arsenic, antimony, thorium, dentin
4 fluorite, iron, nickel
4 to 4.5 platinum, steel
5 apatite, cobalt, zirconium, palladium, tooth enamel, obsidian (volcanic glass)
5.5 beryllium, molybdenum, hafnium
6 orthoclase, titanium, manganese, germanium, niobium, rhodium, uranium
6 to 7 glass, fused quartz, iron pyrite, silicon, ruthenium, iridium, tantalum, opal
7 quartz, vanadium, osmium, rhenium
7.5 to 8 hardened steel, tungsten, emerald, spinel
8 topaz, cubic zirconia
8.5 chrysoberyl, chromium, silicon nitride
9-9.5 corundum, silicon carbide (carborundum), tungsten carbide, titanium carbide, stishovite
9.5–10 rhenium diboride, tantalum carbide, titanium diboride, boron nitride, boron [11][12][13]

[14].


10 diamond
>10 nanocrystalline diamond (hyperdiamond, ultrahard fullerite)

Hardness (Vickers)

Comparison between Hardness (Mohs) and Hardness (Vickers):[15]

Mineral
name 		Hardness (Mohs) Hardness (Vickers)
kg/mm2
Graphite 1 - 2 VHN10=7 - 11
Tin 1½ - 2 VHN10=7 - 9
Bismuth 2 - 2½ VHN100=16 - 18
Gold 2½ - 3 VHN10=30 - 34
Silver 2½ - 3 VHN100=61 - 65
Chalcocite 2½ - 3 VHN100=84 - 87
Copper 2½ - 3 VHN100=77 - 99
Galena 2½ 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 5½ 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 7½ VHN100=1,310
Chromium 9 VHN100=1,875 - 2,000

See also

References

  1. ↑ 1.0 1.1 Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 22 Feb. 2009 "Mohs hardness."
  2. ↑ Theophrastus on Stones
  3. ↑ Pliny the Elder.Naturalis Historia.Book 37.Chap. 15. ADamas: six varieties of it. Two remedies.
  4. ↑ Pliny the Elder.Naturalis Historia.Book 37.Chap. 76. The methods of testing precious stones.
  5. ↑ Learn science, Intermediate p. 42
  6. ↑ American Federation of Mineralogical Societies. "Mohs Scale of Mineral Hardness"
  7. ↑ Amethyst Galleries' Mineral Gallery What is important about hardness?
  8. ↑ Inland Lapidary Mineral Hardness and Hardness Scales
  9. ↑ William S. Cordua (1998). "The Hardness of Minerals and Rocks". Lapidary Digest. http://www.gemcutters.org/LDA/hardness.htm. Retrieved 2007-08-19. Hosted at International Lapidary Association
  10. ↑ L. I. berger "semiconductor materials" CRC press, 1996 ISBN 0849389127, p. 126
  11. ↑ Script error
  12. ↑ Script error. Open access:[1]
  13. ↑ Script error
  14. ↑ Script error. Open access: [2]
  15. ↑ "Mindat.org". http://www.mindat.org/min-1911.html.
  • Mohs hardness of elements is taken from G.V. Samsonov (Ed.) in Handbook of the physicochemical properties of the elements, IFI-Plenum, New York, USA, 1968.
  • Cordua, William S. "The Hardness of Minerals and Rocks". Lapidary Digest, c. 1990.
Mineral identification
af:Mohs se hardheidskaal

ar:مقياس موس bn:কাঠিন্য মাত্রা be:Шкала Моаса be-x-old:Шкала Моаса bs:Mohsova skala tvrdoće bg:Скала на Моос ca:Duresa Mohs cs:Mohsova stupnice tvrdosti da:Mohs' skala de:Härte#Härteprüfung nach Mohs et:Mohsi astmik el:Κλίμακα Μος es:Escalas de dureza eo:Mohs-skalo eu:Mohs eskala fa:سختی موس fr:Échelle de Mohs gl:Escala de Mohs ko:모스 굳기계 hr:Mohsova ljestvica id:Skala Mohs is:Mohs kvarði it:Scala di Mohs he:סולם מוס jv:Skala Mohs ka:მოოსის სკალა lv:Mosa skala lt:Moso skalė hu:Mohs-féle keménységi skála mk:Мосова скала ml:മോസ് ധാതുകാഠിന്യമാനകം mn:Моссын шатлал nl:Hardheidsschaal van Mohs ja:モース硬度 no:Mohs skala nn:Mohs hardleiksskala nds:Mohshard pl:Skala twardości Mohsa pt:Escala de Mohs ro:Scara de duritate Mohs ru:Шкала Мооса sah:Моос шкалаата simple:Mohs scale of mineral hardness sk:Mohsova stupnica tvrdosti sl:Mohsova trdotna lestvica sr:Тврдоћа по Мосовој скали sh:Mosova skala fi:Mohsin kovuus sv:Mohs hårdhetsskala ta:மோவின் அளவுகோல் th:สเกลของโมส์ tr:Mohs sertlik skalası uk:Шкала Мооса vi:Thang độ cứng Mohs zh:摩氏硬度


...