Mohs scale of mineral

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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 .[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]

Contents

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1 Minerals

2 Intermediate hardness

3 Hardness (Vickers)

4 See also

5 References

[edit]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 Mohs hardness Mineral Chemical formula Absolute hardness Image

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

2 Mohs hardness Mineral Chemical formula Absolute hardness Image

7 Quartz SiO2 100

– – 8 Topaz Al2SiO4(OH ,F )2 200

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 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]

[edit]Intermediate hardness

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

Hardness Substance or mineral

0.2–0.3 caesium, rubidium

3 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, , , aluminium, , lanthanum, cerium, Jet_(lignite) (lignite)

3 calcite, copper, arsenic, antimony, , dentin

4 fluorite, ,

4 to 4.5 platinum, steel

5 apatite, cobalt, zirconium, palladium, tooth enamel, obsidian (volcanic glass)

5.5 beryllium, , hafnium

6 orthoclase, , manganese, germanium, niobium, rhodium, uranium

6 to 7 glass, fused quartz, iron pyrite, silicon, ruthenium, iridium, , opal

7 quartz, , osmium, rhenium

7.5 to 8 hardened steel, , emerald, spinel

8 topaz, cubic zirconia

4 8.5 chrysoberyl, , silicon nitride

9-9.5 corundum, silicon carbide (carborundum), tungsten carbide, titanium carbide, stishovite

rhenium diboride, tantalum carbide, titanium diboride, boron nitride, boron [11][12][13]

9.5–10 [14].

10 diamond >10 nanocrystalline diamond (hyperdiamond, ultrahard fullerite) [edit]Hardness (Vickers)

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

Mineral Hardness (Vickers) Hardness (Mohs) name 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

5 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

[edit]See also

. Brinell scale . Knoop hardness test . Hardness . Meyer hardness test . of the elements (data page) [edit]References

6 1. ^ a b 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. Retrieved

2007-08-19. Hosted at International Lapidary Association

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:[1]

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: [2]

15. ^ "Mindat.org".

. 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.

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