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Mohs scale of mineral hardness

January 07, 2023

The Mohs scale of mineral hardness (/moʊz/) is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material.

Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale

The scale was introduced in 1812 by the German geologist and mineralogist Friedrich Mohs, in his book "Versuch einer Elementar-Methode zur naturhistorischen Bestimmung und Erkennung der Fossilien";[1][2] it is one of several definitions of hardness in materials science, some of which are more quantitative.[3]

The method of comparing hardness by observing which minerals can scratch others is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c.  300 BC, followed by Pliny the Elder in his Naturalis Historia, c.  AD 77.[4][5][6] The Mohs scale is useful for identification of minerals in the field, but is not an accurate predictor of how well materials endure in an industrial setting – toughness.[7]

Minerals

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 chemically pure solids found in nature. Rocks are made up of one or more minerals. 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, 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 be between 4 and 5.[8]

"Scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Frequently, materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number. While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number.[9]

Each of the ten hardness values in the Mohs scale is represented by a reference mineral, most of which are widespread in rocks.

The Mohs scale is an 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 the comparison with the absolute hardness measured by a sclerometer, with pictorial examples.[10][11]

Mohs hardness Reference mineral Chemical formula Absolute hardness[12] Image
1 Talc Mg3Si4O10(OH)2 1  
2 Gypsum CaSO4·2H2O 2  
3 Calcite CaCO3 14  
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  
9 Corundum Al2O3 400  
10 Diamond C 1500  

Using some ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. On the Mohs scale, a streak plate (unglazed porcelain) has a hardness of approximately 7.[2] Other useful comparators are: finger nail (2.5), copper coin (3.5), knife blade (5.5), steel nail (6.5), masonry drill bit (8.5).[13]

Intermediate hardness

The hardness of some minerals is intermediate between two of the Mohs scale reference minerals. Some examples are shown in the table:

Other substances

Some solid substances, which are not minerals, have been assigned a hardness on the Mohs scale. However, if the substance is actually a mixture of other substances, hardness can be difficult to determine or may be misleading or meaningless. For example, some sources have assigned a Mohs hardness of 6 or 7 to granite, but this should be treated with caution because granite is a rock made of several minerals, each with its own Mohs hardness (e.g. topaz-rich granite contains: topaz - hardness 8, quartz - hardness 7, orthoclase feldspar - hardness 6, plagioclase feldspar - hardness 6 to 6.5, mica - hardness 2 to 4).

Hardness Substance[14]
0.2–0.3 caesium, rubidium
0.5–0.6 lithium, sodium, potassium, candle wax
1.5 gallium, strontium, barium, thallium
2 hexagonal boron nitride,[15] calcium, wood, dry ice (solid form of carbon dioxide)
2–2.5 alpha-keratin,[16] plastic
2.5–3 lanthanum, jet
3 thorium, dentin, chalk,[17] brass, bronze
4–4.5 ordinary steel
5 tooth enamel, zirconium, obsidian (volcanic glass)
5.5 beryllium, molybdenum, hafnium, glass, cobalt
6 manganese, germanium, niobium, uranium, rhodium
6–7 fused quartz, silicon, ruthenium, iridium, tantalum, opal, concrete, granite
7 rhenium, porcelain
8 cubic zirconia, hardened steel[18]
8.5 silicon nitride, tantalum carbide
9 tungsten carbide, titanium nitride
9–9.5 silicon carbide (carborundum), tantalum carbide, zirconium carbide, beryllium carbide, titanium carbide, aluminium boride, boron carbide.[19][20]
9.5–near 10 boron, boron nitride, rhenium diboride (a-axis),[21] titanium diboride, boron carbide[17]

Use

Despite its lack of precision, the Mohs scale is relevant for field geologists, who use the scale to roughly identify minerals using scratch kits. The Mohs scale hardness of minerals can be commonly found in reference sheets.

Mohs hardness is useful in milling. It allows assessment of which kind of mill will best reduce a given product whose hardness is known.[22] The scale is used at electronic manufacturers for testing the resilience of flat panel display components (such as cover glass for LCDs or encapsulation for OLEDs), as well as to evaluate the hardness of touch screens in consumer electronics.[23]

Comparison with Vickers scale

Comparison between Mohs hardness and Vickers hardness:[24]

Mineral
name 		Hardness (Mohs) Hardness (Vickers)
(kg/mm2)
Graphite 1–2 VHN10 = 7–11
Tin 1.5 VHN10 = 7–9
Bismuth 2–2.5 VHN100 = 16–18
Gold 2.5 VHN10 = 30–34
Silver 2.5 VHN100 = 61–65
Chalcocite 2.5–3 VHN100 = 84–87
Copper 2.5–3 VHN100 = 77–99
Galena 2.5 VHN100 = 79–104
Sphalerite 3.5–4 VHN100 = 208–224
Heazlewoodite 4 VHN100 = 230–254
Carrollite 4.5–5.5 VHN100 = 507–586
Goethite 5–5.5 VHN100 = 667
Hematite 5–6 VHN100 = 1,000–1,100
Chromite 5.5 VHN100 = 1,278–1,456
Anatase 5.5–6 VHN100 = 616–698
Rutile 6–6.5 VHN100 = 894–974
Pyrite 6–6.5 VHN100 = 1,505–1,520
Bowieite 7 VHN100 = 858–1,288
Euclase 7.5 VHN100 = 1,310
Chromium 8.5 VHN100 = 1,875–2,000

See also

References

  1. ^ von Groth, Paul Heinrich (1926). Entwicklungsgeschichte der Mineralogischen Wissenschaften [History of the development of the mineralogical sciences] (in German). Berlin: Springer. p. 250. ISBN 9783662409107. In demselben Jahre (1812) wurde MOHS als Professor am Joanneum angestellt und veröffentliche den ersten Teil seines Werkes "Versuch einer Elementarmethode zur naturhistorischen Bestimmung und Erkennung der Fossilien", in welcher die bekannte Härteskala aufgestellt wurde. [In the same year (1812) MOHS was employed as a professor at the Joanneum and published the first part of his work "Attempt at an elementary method for the natural-historical determination and recognition of fossils", in which the well-known hardness scale was set up.]
  2. ^ a b "Mohs hardness" in Encyclopædia Britannica Online
  3. ^ "Mohs scale of hardness". Mineralogical Society of America. Retrieved 10 February 2021.
  4. ^ Theophrastus. Theophrastus on Stones. Retrieved 2011-12-10 – via Farlang.com.
  5. ^ Pliny the Elder. "Book 37, Chap. 15". Naturalis Historia. Adamas: Six varieties of it. Two remedies.
  6. ^ Pliny the Elder. "Book 37, Chap. 76". Naturalis Historia. The methods of testing precious stones.
  7. ^ . Materials Mechanical Hardness. Non-Destructive Testing Resource Center. Archived from the original on 2014-02-14.
  8. ^ American Federation of Mineralogical Societies. "Mohs Scale of Mineral Hardness". amfed.org
  9. ^ Geels, Kay. , pp. 5–13 in Materialographic Preparation from Sorby to the Present. Struers A/S, Copenhagen, Denmark - archived Mar 7 2016
  10. ^ Amethyst Galleries' Mineral Gallery . galleries.com
  11. ^ Mineral Hardness and Hardness Scales 2008-10-17 at the Wayback Machine. Inland Lapidary
  12. ^ Mukherjee, Swapna (2012). Applied Mineralogy: Applications in Industry and Environment. Springer Science & Business Media. p. 373. ISBN 978-94-007-1162-4.
  13. ^ "Mohs Hardness Scale". Fundamental Geologic Principles. National Park Service. Retrieved 18 November 2022.
  14. ^ Samsonov, G.V., ed. (1968). "Mechanical Properties of the Elements". Handbook of the Physicochemical Properties of the Elements. New York: IFI-Plenum. p. 432. doi:10.1007/978-1-4684-6066-7. ISBN 978-1-4684-6068-1.
  15. ^ Berger, Lev I. (1996). Semiconductor Materials (First ed.). Boca Raton, FL: CRC Press. p. 126. ISBN 978-0849389122.
  16. ^ "Mohs Hardness Scale: Testing the Resistance to Being Scratched". geology.com.
  17. ^ a b "Reade Advanced Materials - Mohs' Hardness (Typical) of Abrasives". www.reade.com. Retrieved 2021-08-09.
  18. ^ "Mohs Hardness Scale: Testing the Resistance to Being Scratched". geology.com. Retrieved 2021-08-09.
  19. ^ "Material hardness tables". www.tedpella.com. Retrieved 2019-05-09.
  20. ^ "Hardness table" (PDF). Retrieved 2019-05-09.
  21. ^ Levine, Jonathan B.; Tolbert, Sarah H.; Kaner, Richard B. (2009). (PDF). Advanced Functional Materials. 19 (22): 3526–3527. doi:10.1002/adfm.200901257. S2CID 98675890. Archived from the original (PDF) on 2016-03-04. Retrieved 2015-12-08.
  22. ^ "Size reduction, comminution". Grinding and milling. PowderProcess.net. Retrieved 27 October 2017.
  23. ^ Purdy, Kevin (16 May 2014). "Hardness is not toughness: Why your phone's screen may not scratch, but will shatter". Computerworld. IDG Communications Inc. Retrieved 16 April 2021.
  24. ^ Ralph, Jolyon. "Welcome to mindat.org". mindat.org. Hudson Institute of Mineralogy. Retrieved April 16, 2017.

Further reading

  • Cordua, William S. (c. 1990). "The Hardness of Minerals and Rocks". Lapidary Digest – via gemcutters.org.

January 07, 2023
mohs, scale, mineral, hardness, qualitative, ordinal, scale, from, characterizing, scratch, resistance, various, minerals, through, ability, harder, material, scratch, softer, material, mohs, hardness, containing, specimen, each, mineral, point, hardness, scal. The Mohs scale of mineral hardness m oʊ z is a qualitative ordinal scale from 1 to 10 characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material Mohs hardness kit containing one specimen of each mineral on the ten point hardness scale The scale was introduced in 1812 by the German geologist and mineralogist Friedrich Mohs in his book Versuch einer Elementar Methode zur naturhistorischen Bestimmung und Erkennung der Fossilien 1 2 it is one of several definitions of hardness in materials science some of which are more quantitative 3 The method of comparing hardness by observing which minerals can scratch others is of great antiquity having been mentioned by Theophrastus in his treatise On Stones c 300 BC followed by Pliny the Elder in his Naturalis Historia c AD 77 4 5 6 The Mohs scale is useful for identification of minerals in the field but is not an accurate predictor of how well materials endure in an industrial setting toughness 7 Contents 1 Minerals 1 1 Intermediate hardness 2 Other substances 3 Use 4 Comparison with Vickers scale 5 See also 6 References 7 Further readingMinerals EditThe 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 chemically pure solids found in nature Rocks are made up of one or more minerals 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 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 be between 4 and 5 8 Scratching a material for the purposes of the Mohs scale means creating non elastic dislocations visible to the naked eye Frequently materials that are lower on the Mohs scale can create microscopic non elastic dislocations on materials that have a higher Mohs number While these microscopic dislocations are permanent and sometimes detrimental to the harder material s structural integrity they are not considered scratches for the determination of a Mohs scale number 9 Each of the ten hardness values in the Mohs scale is represented by a reference mineral most of which are widespread in rocks The Mohs scale is an 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 the comparison with the absolute hardness measured by a sclerometer with pictorial examples 10 11 Mohs hardness Reference mineral Chemical formula Absolute hardness 12 Image1 Talc Mg3Si4O10 OH 2 1 2 Gypsum CaSO4 2H2O 2 3 Calcite CaCO3 14 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 9 Corundum Al2O3 400 10 Diamond C 1500 Using some ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale On the Mohs scale a streak plate unglazed porcelain has a hardness of approximately 7 2 Other useful comparators are finger nail 2 5 copper coin 3 5 knife blade 5 5 steel nail 6 5 masonry drill bit 8 5 13 Intermediate hardness Edit The hardness of some minerals is intermediate between two of the Mohs scale reference minerals Some examples are shown in the table Hardness Mineral1 5 todorokite wakabayashilite idrialite dimorphite2 5 linarite ulexite kinoite cylindrite3 5 adamite strontianite roselite ludlamite4 5 conichalcite duftite colemanite lindgrenite5 5 perovskite chromite bavenite agrellite6 5 baddeleyite chloritoid berlinite cuprospinel7 5 zircon euclase hambergite grandidierite8 5 chrysoberyl tongbaite9 25 moissaniteOther substances EditSome solid substances which are not minerals have been assigned a hardness on the Mohs scale However if the substance is actually a mixture of other substances hardness can be difficult to determine or may be misleading or meaningless For example some sources have assigned a Mohs hardness of 6 or 7 to granite but this should be treated with caution because granite is a rock made of several minerals each with its own Mohs hardness e g topaz rich granite contains topaz hardness 8 quartz hardness 7 orthoclase feldspar hardness 6 plagioclase feldspar hardness 6 to 6 5 mica hardness 2 to 4 This section needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Mohs scale of mineral hardness news newspapers books scholar JSTOR November 2022 Learn how and when to remove this template message Hardness Substance 14 0 2 0 3 caesium rubidium0 5 0 6 lithium sodium potassium candle wax1 5 gallium strontium barium thallium2 hexagonal boron nitride 15 calcium wood dry ice solid form of carbon dioxide 2 2 5 alpha keratin 16 plastic2 5 3 lanthanum jet3 thorium dentin chalk 17 brass bronze4 4 5 ordinary steel5 tooth enamel zirconium obsidian volcanic glass 5 5 beryllium molybdenum hafnium glass cobalt6 manganese germanium niobium uranium rhodium6 7 fused quartz silicon ruthenium iridium tantalum opal concrete granite7 rhenium porcelain8 cubic zirconia hardened steel 18 8 5 silicon nitride tantalum carbide9 tungsten carbide titanium nitride9 9 5 silicon carbide carborundum tantalum carbide zirconium carbide beryllium carbide titanium carbide aluminium boride boron carbide 19 20 9 5 near 10 boron boron nitride rhenium diboride a axis 21 titanium diboride boron carbide 17 Use EditDespite its lack of precision the Mohs scale is relevant for field geologists who use the scale to roughly identify minerals using scratch kits The Mohs scale hardness of minerals can be commonly found in reference sheets Mohs hardness is useful in milling It allows assessment of which kind of mill will best reduce a given product whose hardness is known 22 The scale is used at electronic manufacturers for testing the resilience of flat panel display components such as cover glass for LCDs or encapsulation for OLEDs as well as to evaluate the hardness of touch screens in consumer electronics 23 Comparison with Vickers scale EditComparison between Mohs hardness and Vickers hardness 24 Mineralname Hardness Mohs Hardness Vickers kg mm2 Graphite 1 2 VHN10 7 11Tin 1 5 VHN10 7 9Bismuth 2 2 5 VHN100 16 18Gold 2 5 VHN10 30 34Silver 2 5 VHN100 61 65Chalcocite 2 5 3 VHN100 84 87Copper 2 5 3 VHN100 77 99Galena 2 5 VHN100 79 104Sphalerite 3 5 4 VHN100 208 224Heazlewoodite 4 VHN100 230 254Carrollite 4 5 5 5 VHN100 507 586Goethite 5 5 5 VHN100 667Hematite 5 6 VHN100 1 000 1 100Chromite 5 5 VHN100 1 278 1 456Anatase 5 5 6 VHN100 616 698Rutile 6 6 5 VHN100 894 974Pyrite 6 6 5 VHN100 1 505 1 520Bowieite 7 VHN100 858 1 288Euclase 7 5 VHN100 1 310Chromium 8 5 VHN100 1 875 2 000See also EditBrinell scale Geological Strength Index Hardnesses of the elements data page Knoop hardness test Meyer hardness test Pencil hardness Rockwell scale Rosiwal scale Scratch hardness Superhard materialReferences Edit von Groth Paul Heinrich 1926 Entwicklungsgeschichte der Mineralogischen Wissenschaften History of the development of the mineralogical sciences in German Berlin Springer p 250 ISBN 9783662409107 In demselben Jahre 1812 wurde MOHS als Professor am Joanneum angestellt und veroffentliche den ersten Teil seines Werkes Versuch einer Elementarmethode zur naturhistorischen Bestimmung und Erkennung der Fossilien in welcher die bekannte Harteskala aufgestellt wurde In the same year 1812 MOHS was employed as a professor at the Joanneum and published the first part of his work Attempt at an elementary method for the natural historical determination and recognition of fossils in which the well known hardness scale was set up a b Mohs hardness in Encyclopaedia Britannica Online Mohs scale of hardness Mineralogical Society of America Retrieved 10 February 2021 Theophrastus Theophrastus on Stones Retrieved 2011 12 10 via Farlang com Pliny the Elder Book 37 Chap 15 Naturalis Historia Adamas Six varieties of it Two remedies Pliny the Elder Book 37 Chap 76 Naturalis Historia The methods of testing precious stones Hardness Materials Mechanical Hardness Non Destructive Testing Resource Center Archived from the original on 2014 02 14 American Federation of Mineralogical Societies Mohs Scale of Mineral Hardness amfed org Geels Kay The True Microstructure of Materials pp 5 13 in Materialographic Preparation from Sorby to the Present Struers A S Copenhagen Denmark archived Mar 7 2016 Amethyst Galleries Mineral Gallery What is important about hardness galleries com Mineral Hardness and Hardness Scales Archived 2008 10 17 at the Wayback Machine Inland Lapidary Mukherjee Swapna 2012 Applied Mineralogy Applications in Industry and Environment Springer Science amp Business Media p 373 ISBN 978 94 007 1162 4 Mohs Hardness Scale Fundamental Geologic Principles National Park Service Retrieved 18 November 2022 Samsonov G V ed 1968 Mechanical Properties of the Elements Handbook of the Physicochemical Properties of the Elements New York IFI Plenum p 432 doi 10 1007 978 1 4684 6066 7 ISBN 978 1 4684 6068 1 Berger Lev I 1996 Semiconductor Materials First ed Boca Raton FL CRC Press p 126 ISBN 978 0849389122 Mohs Hardness Scale Testing the Resistance to Being Scratched geology com a b Reade Advanced Materials Mohs Hardness Typical of Abrasives www reade com Retrieved 2021 08 09 Mohs Hardness Scale Testing the Resistance to Being Scratched geology com Retrieved 2021 08 09 Material hardness tables www tedpella com Retrieved 2019 05 09 Hardness table PDF Retrieved 2019 05 09 Levine Jonathan B Tolbert Sarah H Kaner Richard B 2009 Advancements in the search for superhard ultra incompressible metal borides PDF Advanced Functional Materials 19 22 3526 3527 doi 10 1002 adfm 200901257 S2CID 98675890 Archived from the original PDF on 2016 03 04 Retrieved 2015 12 08 Size reduction comminution Grinding and milling PowderProcess net Retrieved 27 October 2017 Purdy Kevin 16 May 2014 Hardness is not toughness Why your phone s screen may not scratch but will shatter Computerworld IDG Communications Inc Retrieved 16 April 2021 Ralph Jolyon Welcome to mindat org mindat org Hudson Institute of Mineralogy Retrieved April 16 2017 Further reading EditCordua William S c 1990 The Hardness of Minerals and Rocks Lapidary Digest via gemcutters org Retrieved from https en wikipedia org w index php title Mohs scale of mineral hardness amp oldid 1131850328, wikipedia, wiki, book, books, library,

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