Mohs scale of mineral hardness

Mohs scale of mineral hardness
1
Mohs scale of mineral hardness
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
1
Talc
Mg3Si4O10(OH)2
1
2
Gypsum
CaSO4·2H2O
3
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
Image
Mohs scale of mineral hardness
2
9
Corundum
Al2O3
400
10
Diamond
C
1600
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
1.5
2
2.5 to 3
talc
gallium, strontium, indium, tin, barium, thallium, lead, graphite
[10]
hexagonal boron nitride,
calcium, selenium, cadmium, sulfur, tellurium, bismuth
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
5
5.5
platinum, steel
apatite, cobalt, zirconium, palladium, tooth enamel, obsidian (volcanic glass)
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
7.5 to 8
8
8.5
9-9.5
9.5–10
quartz, vanadium, osmium, rhenium
hardened steel, tungsten, emerald, spinel
topaz, cubic zirconia
chrysoberyl, chromium, silicon nitride
corundum, silicon carbide (carborundum), tungsten carbide, titanium carbide, stishovite
rhenium diboride, tantalum carbide, titanium diboride, boron nitride, boron
10
diamond
>10
nanocrystalline diamond (hyperdiamond, ultrahard fullerite)
[11] [12] [13] [14]
.
Mohs scale of mineral hardness
3
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
References
[1] Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 22 Feb. 2009 "Mohs hardness." (http:/ / www. britannica. com/ EBchecked/
topic/ 387714/ Mohs-hardness)
[2] Theophrastus on Stones (http:/ / www. farlang. com/ gemstones/ theophrastus-on-stones/ page_148/ view?searchterm=scratch)
[3] Pliny the Elder.Naturalis Historia.Book 37.Chap. 15. ADamas: six varieties of it. Two remedies. (http:/ / www. perseus. tufts. edu/ cgi-bin/
ptext?lookup=Plin. + Nat. + 37. 15)
[4] Pliny the Elder.Naturalis Historia.Book 37.Chap. 76. The methods of testing precious stones. (http:/ / www. perseus. tufts. edu/ cgi-bin/
ptext?lookup=Plin. + Nat. + 37. 76)
[5] Learn science, Intermediate p. 42
[6] American Federation of Mineralogical Societies. "Mohs Scale of Mineral Hardness" (http:/ / www. amfed. org/ t_mohs. htm)
[7] Amethyst Galleries' Mineral Gallery What is important about hardness? (http:/ / www. galleries. com/ minerals/ hardness. htm)
[8] Inland Lapidary Mineral Hardness and Hardness Scales (http:/ / www. inlandlapidary. com/ user_area/ hardness. asp)
[9] William S. Cordua (1998). "The Hardness of Minerals and Rocks" (http:/ / www. gemcutters. org/ LDA/ hardness. htm). Lapidary Digest. .
Retrieved 2007-08-19. Hosted at International Lapidary Association (http:/ / www. gemcutters. org/ )
[10] L. I. berger "semiconductor materials" CRC press, 1996 ISBN 0849389127, p. 126
[11] Weintraub E. (1911). "On the properties and preparation of the element boron.". J. Ind. Eng. Chem. 3 (5): 299–301.
doi:10.1021/ie50029a007.
[12] Solozhenko, V. L.; Kurakevych O. O.; Oganov A. R. (2008). "On the hardness of a new boron phase, orthorhombic γ-B28". Journal of
Superhard Materials 30 (6): 428–429. doi:10.3103/s1063457608060117.. Open access: (http:/ / mysbfiles. stonybrook. edu/ ~aoganov/ files/
JSM-2008-6b-e. pdf)
Mohs scale of mineral hardness
[13] Zarechnaya, E. Yu.; Dubrovinsky, L.; Dubrovinskaia, N.; Filinchuk, Y.; Chernyshov, D.; Dmitriev, V.; Miyajima, N.; El Goresy, A. et al.
(2009). "Superhard semiconducting optically transparent high pressure phase of boron". Phys. Rev. Lett. 102 (18): 185501.
Bibcode 2009PhRvL.102r5501Z. doi:10.1103/physrevlett.102.185501. PMID 19518885.
[14] Oganov A.R., Solozhenko V.L. (2009). "Boron: a hunt for superhard polymorphs". Journal of Superhard Materials 31: 285-291.. Open
access: (http:/ / mysbfiles. stonybrook. edu/ ~aoganov/ files/ Boron-history-JSM. pdf)
[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" (http://www.gemcutters.org/LDA/hardness.htm).
Lapidary Digest, c. 1990.
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Article Sources and Contributors
Article Sources and Contributors
Mohs scale of mineral hardness Source: http://en.wikipedia.org/w/index.php?oldid=444930318 Contributors: 198.144.199.xxx, 345Kai, Adamv88, Afluegel, Alansohn, Albedo, Amorphagate,
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Image Sources, Licenses and Contributors
Image:Talc block.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Talc_block.jpg License: Public Domain Contributors: EugeneZelenko, Sanao, Saperaud, Wela49
Image:Gypse Arignac.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Gypse_Arignac.jpg License: Creative Commons Attribution-Sharealike 3.0,2.5,2.0,1.0 Contributors: Didier
Descouens
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Image:Fluorite with Iron Pyrite.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Fluorite_with_Iron_Pyrite.jpg License: Creative Commons Attribution 2.5 Contributors: Original
uploader was H at en.wikipedia
Image:Apatite crystals.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Apatite_crystals.jpg License: Public Domain Contributors: OG59, Rocket000, Überraschungsbilder, 1
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Image:Topaz cut.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Topaz_cut.jpg License: GNU Free Documentation License Contributors: w:de:Benutzer:Wela49Wela49
Image:Cut Ruby.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Cut_Ruby.jpg License: Public Domain Contributors: User:Bkell
Image:Rough diamond.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Rough_diamond.jpg License: Public Domain Contributors: Unknown USGS employee
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