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{{short description|Qualitative scale characterizing scratch resistance}} |
{{short description|Qualitative scale characterizing scratch resistance}} |
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{{use dmy dates|date=August 2024}} |
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[[File:Mohssche-haerteskala hg.jpg|thumb|alt=Open wooden box with ten compartments, each containing a numbered mineral specimen.|Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale]] |
[[File:Mohssche-haerteskala hg.jpg|thumb|alt=Open wooden box with ten compartments, each containing a numbered mineral specimen.|Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale]] |
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The '''Mohs scale''' |
The '''Mohs scale''' ({{IPAc-en|m|ou|z}} {{respell|MOHZ}}) of mineral hardness is a [[Qualitative property|qualitative]] [[ordinal scale]], from 1 to 10, characterizing [[scratch hardness|scratch resistance]] of [[mineral]]s through the ability of harder material to scratch softer material. |
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The scale was introduced in 1812 by the German [[geologist]] and [[Mineralogy|mineralogist]] [[Friedrich Mohs]], in his book |
The scale was introduced in 1812 by the German [[geologist]] and [[Mineralogy|mineralogist]] [[Friedrich Mohs]], in his book {{lang|de|Versuch einer Elementar-Methode zur naturhistorischen Bestimmung und Erkennung der Fossilien}} (English: Attempt at an elementary method for the natural-historical determination and recognition of fossils);<ref name=VonGroth1926>{{cite book | title=Entwicklungsgeschichte der Mineralogischen Wissenschaften | trans-title=History of the development of the mineralogical sciences | url=https://books.google.com/books?id=tD0LAQAAIAAJ&q=+Härteskala+1812 | publisher=Springer | last=von Groth | first=Paul Heinrich | date=1926 | publication-place=Berlin | page=250 | isbn=9783662409107 | lang=de }}</ref><ref name=Brit>{{cite encyclopedia |url=https://www.britannica.com/EBchecked/topic/387714/Mohs-hardness |title=Mohs hardness |encyclopedia=[[Encyclopædia Britannica]] |edition=online }}</ref>{{efn| |
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: {{lang|de|In demselben Jahre (1812) wurde MOHS als Professor am Joanneum angestellt und veröffentliche den ersten Teil seines Werkes {{noitalic|Versuch einer Elementarmethode zur naturhistorischen Bestimmung und Erkennung der Fossilien}}, in welcher die bekannte Härteskala aufgestellt wurde.}} — {{harvp|von Groth|1926}} |
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: 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.<ref name=VonGroth1926/> |
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}} it is one of several definitions of [[hardness comparison|hardness]] in [[materials science]], some of which are more quantitative.<ref name="MinSocAm">{{cite web |title=Mohs scale of hardness |publisher=[[Mineralogical Society of America]] |url=http://www.minsocam.org/MSA/collectors_corner/article/mohs.htm |access-date=10 February 2021}}</ref> |
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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'', {{circa| 300 BC}}, followed by [[Pliny the Elder]] in his ''[[Natural History (Pliny)|Naturalis Historia]]'', {{circa| AD 77}}.<ref>{{cite book |url=http://www.farlang.com/gemstones/theophrastus-on-stones/page_148/view?searchterm=scratch |title=Theophrastus on Stones |author=[[Theophrastus]] |via=Farlang.com |access-date=2011-12-10}}</ref><ref>{{cite book |author=[[Pliny the Elder]] |title=Naturalis Historia |chapter=Book 37, Chap. 15 |chapter-url=https://www.perseus.tufts.edu/cgi-bin/ptext?lookup=Plin.+Nat.+37.15 |quote=''Adamas'': Six varieties of it. Two remedies.}}</ref><ref>{{cite book |author=[[Pliny the Elder]] |title=[[Naturalis Historia]] |chapter=Book 37, Chap. 76 |chapter-url=https://www.perseus.tufts.edu/cgi-bin/ptext?lookup=Plin.+Nat.+37.76 |quote=The methods of testing precious stones.}}</ref> 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.<ref>{{cite web |url=http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/Hardness.htm |title=Hardness |archive-url=https://web.archive.org/web/20140214185403/http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/Hardness.htm |archive-date=2014-02-14 |publisher=Non-Destructive Testing Resource Center |series=Materials Mechanical Hardness}}</ref> |
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'', {{circa| 300 BC}}, followed by [[Pliny the Elder]] in his ''[[Natural History (Pliny)|Naturalis Historia]]'', {{circa| AD 77}}.<ref>{{cite book |url=http://www.farlang.com/gemstones/theophrastus-on-stones/page_148/view?searchterm=scratch |title=Theophrastus on Stones |author=[[Theophrastus]] |via=Farlang.com |access-date=2011-12-10}}</ref><ref>{{cite book |author=[[Pliny the Elder]] |title=Naturalis Historia |chapter=Book 37, Chap. 15 |chapter-url=https://www.perseus.tufts.edu/cgi-bin/ptext?lookup=Plin.+Nat.+37.15 |quote=''Adamas'': Six varieties of it. Two remedies.}}</ref><ref>{{cite book |author=[[Pliny the Elder]] |title=[[Naturalis Historia]] |chapter=Book 37, Chap. 76 |chapter-url=https://www.perseus.tufts.edu/cgi-bin/ptext?lookup=Plin.+Nat.+37.76 |quote=The methods of testing precious stones.}}</ref> The Mohs scale is useful for identification of minerals in the [[Field research|field]], but is not an accurate predictor of how well materials endure in an industrial setting.<ref>{{cite web |url=http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/Hardness.htm |title=Hardness |archive-url=https://web.archive.org/web/20140214185403/http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/Hardness.htm |archive-date=2014-02-14 |publisher=Non-Destructive Testing Resource Center |series=Materials Mechanical Hardness}}</ref> |
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==Reference minerals== |
==Reference minerals== |
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The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral |
The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to visibly scratch another mineral. [[Mineral]]s are chemically pure solids found in nature. [[Rock (geology)|Rock]]s are mixtures of one or more minerals. |
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:{| style="float:right;border:none;background:white;margin-left:2em" |
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| ⚫ | |||
| ⚫ | |||
| ⚫ | |||
|style="padding-left:2em;"| Mohs scale along the horizontal axis matched with <br/>one of the [[absolute hardness]] scales along the <br/>vertical. Diamond (Mohs 10) is 1500 (off scale). |
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[[Diamond]] was the hardest known naturally occurring mineral when the scale was designed, and defines the top of the scale, arbitrarily set at 10. 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.<ref>{{cite web |title=Mohs scale of mineral hardness |publisher=[[American Federation of Mineralogical Societies]] |url=https://www.amfed.org/mohs-scale |via=amfed.org |access-date= }}</ref> |
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" |
Technically, "scratching" a material for the purposes of the Mohs scale means creating non-[[Elasticity (physics)|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.<ref>{{cite report |last=Geels |first=Kay |publication-date=26 April 2000 |section=The true microstructure of materials |pages=5–13 |title=Materialographic Preparation from Sorby to the Present |department=Application notes and guides |series=The Struers metallographic library |publisher=Struers A/S |place=Copenhagen, DK |url=http://www.struers.com/resources/elements/12/2474/35art2.pdf |url-status=dead <!-- presumed --> |archive-url=https://web.archive.org/web/20160307194802/http://www.struers.com/resources/elements/12/2474/35art2.pdf |archive-date=7 March 2016 }}</ref> |
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Each of the ten hardness values in the Mohs scale is represented by a ''reference mineral'', most of which are widespread in rocks. |
Each of the ten hardness values in the Mohs scale is represented by a ''reference mineral'', most of which are widespread in rocks. |
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| ⚫ | |||
| ⚫ | 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 |
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| ⚫ | 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.{{fact|date=October 2024}} The table below shows the comparison with the [[absolute hardness]] measured by a [[sclerometer]], with images of the reference minerals in the rightmost column.<ref>{{cite web |title=What is important about hardness? |department=Amethyst galleries |series=Mineral gallery |url=http://www.galleries.com/minerals/hardness.htm |url-status=dead <!-- presumed --> |access-date= |via=galleries.com |archive-url=https://web.archive.org/web/20061230174242/http://www.galleries.com/minerals/hardness.htm |archive-date=30 December 2006 }}</ref><ref>{{cite web |title=Mineral hardness and hardness scales |publisher=Inland Lapidary |url=http://www.inlandlapidary.com/user_area/hardness.asp |via=inlandlapidary.com |url-status=live <!-- presumed --> |access-date= |archive-url=https://web.archive.org/web/20081017152845/http://www.inlandlapidary.com/user_area/hardness.asp |archive-date=2008-10-17 }}</ref> |
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| ⚫ | |||
:{| class="wikitable sortable" style="text-align:center" |
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! |
! Mohs<br/>hardness |
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! |
! Reference<br/>mineral |
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! |
! Chemical formula |
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! |
! Absolute<br/>hardness<ref>{{cite book |last=Mukherjee |first=Swapna |year=2012 |title=Applied Mineralogy: Applications in industry and environment |publisher=Springer Science & Business Media |isbn=978-94-007-1162-4 |page=373 |url=https://books.google.com/books?id=mllvP7ZmWqkC&pg=PA373 |via=Google books}}</ref> |
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!class="unsortable"| |
!class="unsortable"| Example image |
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|- |
|- |
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|'''1''' |
| '''1''' |
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|[[Talc]] |
| [[Talc]] |
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|Mg<sub>3</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub> |
| {{chem2| Mg3Si4O10(OH)2 }} <!-- Mg<sub>3</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub> --> |
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|1 |
| 1 |
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|[[Image:Talc block.jpg|100px]] |
| [[Image:Talc block.jpg|100px]] |
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|- |
|- |
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|'''2''' |
| '''2''' |
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|[[Gypsum]] |
| [[Gypsum]] |
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|CaSO<sub>4</sub>·2H<sub>2</sub>O |
| {{chem2| Ca SO4 * 2H2O }} <!-- CaSO<sub>4</sub>·2H<sub>2</sub>O --> |
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|2 |
| 2 |
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|[[Image:Gypse Arignac.jpg|100px]] |
| [[Image:Gypse Arignac.jpg|100px]] |
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|- |
|- |
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|'''3''' |
| '''3''' |
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|[[Calcite]] |
| [[Calcite]] |
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|CaCO<sub>3</sub> |
| {{chem2| Ca CO3 }} <!-- CaCO<sub>3</sub> --> |
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|14 |
| 14 |
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|[[Image:Calcite-sample2.jpg|100px]] |
| [[Image:Calcite-sample2.jpg|100px]] |
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|- |
|- |
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|'''4''' |
| '''4''' |
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|[[Fluorite]] |
| [[Fluorite]] |
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|CaF<sub>2</sub> |
| {{chem2| Ca F2 }} <!-- CaF<sub>2</sub> --> |
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|21 |
| 21 |
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|[[Image:Fluorite with Iron Pyrite.jpg|100px]] |
| [[Image:Fluorite with Iron Pyrite.jpg|100px]] |
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|- |
|- |
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|'''5''' |
| '''5''' |
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|[[Apatite]] |
| [[Apatite]] |
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|Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>(OH<sup>−</sup>,Cl<sup>−</sup>,F<sup>−</sup>) |
| {{chem2| Ca5(PO4)3 (OH−,Cl−,F−) }} <!-- Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>(OH<sup>−</sup>,Cl<sup>−</sup>,F<sup>−</sup>) --> |
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|48 |
| 48 |
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|[[Image:Apatite Canada.jpg|100px]] |
| [[Image:Apatite Canada.jpg|100px]] |
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|- |
|- |
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|'''6''' |
| '''6''' |
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|[[Orthoclase|Orthoclase |
| [[Orthoclase|Orthoclase<br/>feldspar]] |
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|KAlSi<sub>3</sub>O<sub>8</sub> |
| {{chem2| K Al Si3O8 }} <!-- KAlSi<sub>3</sub>O<sub>8</sub> --> |
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|72 |
| 72 |
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|[[Image:OrthoclaseBresil.jpg|100px]] |
| [[Image:OrthoclaseBresil.jpg|100px]] |
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|- |
|- |
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|'''7''' |
| '''7''' |
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|[[Quartz]] |
| [[Quartz]] |
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|SiO<sub>2</sub> |
| {{chem2| SiO2 }} <!-- SiO<sub>2</sub> --> |
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|100 |
| 100 |
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|[[Image:Quartz Brésil.jpg|100px]] |
| [[Image:Quartz Brésil.jpg|100px]] |
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|- |
|- |
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|'''8''' |
| '''8''' |
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|[[Topaz]] |
| [[Topaz]] |
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|Al<sub>2</sub>SiO<sub>4</sub>(OH<sup>−</sup>,F<sup>−</sup>)<sub>2</sub> |
| {{chem2| Al2SiO4(OH−,F−)2 }} <!-- Al<sub>2</sub>SiO<sub>4</sub>(OH<sup>−</sup>,F<sup>−</sup>)<sub>2</sub> --> |
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|200 |
| 200 |
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|[[Image:Topaz-120187.jpg|100px]] |
| [[Image:Topaz-120187.jpg|100px]] |
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|- |
|- |
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|'''9''' |
| '''9''' |
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|[[Corundum]] |
| [[Corundum]] |
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|Al<sub>2</sub>O<sub>3</sub> |
| {{chem2| Al2O3 }} <!-- Al<sub>2</sub>O<sub>3</sub> --> |
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|400 |
| 400 |
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|[[Image:Corundum-dtn14b.jpg|100px]] |
| [[Image:Corundum-dtn14b.jpg|100px]] |
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|- |
|- |
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|'''10''' |
| '''10''' |
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|[[Diamond]] |
| [[Diamond]] |
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| {{chem2| C }} <!-- C --> |
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| ⚫ | |||
|1500 |
| 1500 |
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|[[Image:Rough diamond.jpg|100px]] |
| [[Image:Rough diamond.jpg|100px]] |
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|} |
|} |
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==Examples== |
==Examples== |
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| ⚫ | Below is a table of more materials by Mohs scale. Some of them have a hardness between two of the Mohs scale reference minerals. Some solid substances |
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{{More citations needed|section|date=November 2022}} |
{{More citations needed|section|date=November 2022}} |
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| ⚫ | Below is a table of more materials by Mohs scale. Some of them have a hardness between two of the Mohs scale reference minerals. Some solid substances that are not minerals have been assigned a hardness on the Mohs scale. However, hardness can make it difficult to determine if the substance is a mixture of other substances or if it may be misleading or meaningless. For example, some sources have assigned a Mohs hardness of 6 or 7 to granite but it is a rock made of several minerals, each with its own Mohs hardness (e.g. topaz-rich granite contains: topaz — Mohs 8, quartz — Mohs 7, orthoclase — Mohs 6, plagioclase — Mohs 6–6.5, mica — Mohs 2–4). |
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{| class="wikitable" |
:{| class="wikitable" |
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!Hardness |
! Hardness |
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!Substance<ref name= |
! Substance<ref name=Samsonov68>{{cite book | editor-last=Samsonov | editor-first=G.V. | year=1968 | chapter=Mechanical properties of the elements | title=Handbook of the Physicochemical Properties of the Elements | publisher=IFI-Plenum | place=New York, NY | doi=10.1007/978-1-4684-6066-7 | isbn=978-1-4684-6068-1 | page=432 }}</ref> |
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|style="text-align:center;"| 0.2–0.4 |
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| [[Potassium]] |
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| [[Caesium]], [[potassium]], [[rubidium]], [[butter]] |
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|- |
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|style="text-align:center;"| 0.5–0.6 |
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| [[Lithium |
| [[Lithium]] |
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|- |
|- |
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|style="text-align:center;"| 1 |
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| [[Talc]] |
| [[Talc]] |
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|- |
|- |
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|style="text-align:center;"| 1.5 |
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| [[Lead]] |
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| [[Tin]], [[lead]], [[ice]], [[todorokite]], [[wakabayashilite]], [[idrialite]], [[dimorphite]] |
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|- |
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|style="text-align:center;"| 2 |
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| ⚫ | |||
| [[Gypsum]], [[calcium]], [[hardwood]], [[dry ice]] (solid form of [[carbon dioxide]]), [[glauconite]]<ref name="geology.com" /> |
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|- |
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|style="text-align:center;"| 2–2.5 |
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| [[ |
| [[Plastic]] |
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|- |
|- |
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|style="text-align:center;"| 2.5 |
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| [[Zinc]] |
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| [[Native gold|Gold]], [[silver]], [[magnesium]], [[zinc]], [[pearl]], [[amber]], [[ivory]], [[Nail (anatomy)|finger nail]],<ref name="NPS-Hardness">{{cite web | url=https://www.nps.gov/articles/mohs-hardness-scale.htm | title=Mohs Hardness Scale | publisher=[[National Park Service]] | work=Fundamental Geologic Principles | accessdate=18 November 2022}}</ref> [[galena]], [[linarite]], [[ulexite]], [[kinoite]], [[cylindrite]] |
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|- |
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|style="text-align:center;"| 2.5–3 |
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| [[Native copper|Copper |
| [[Native copper|Copper]] |
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|- |
|- |
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|style="text-align:center;"| 3 |
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| [[Brass]] |
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| [[Calcite]], [[thorium]], [[dentin]], [[chalk]],<ref name="reade.com">{{Cite web|title=Reade Advanced Materials - Mohs' Hardness (Typical) of Abrasives|url=https://www.reade.com/reade-resources/reference-educational/reade-reference-chart-particle-property-briefings/32-mohs-hardness-of-abrasives|access-date=2021-08-09|website=www.reade.com}}</ref> [[brass]], [[bronze]] |
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|style="text-align:center;"| 3.5 |
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| [[Adamite]] |
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| [[Platinum]], [[adamite]], [[strontianite]], [[roselite]], [[ludlamite]] |
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|- |
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|style="text-align:center;"| 3.5-4 |
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| [[Sphalerite]] |
| [[Sphalerite]] |
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|- |
|- |
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|style="text-align:center;"| 4 |
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| [[Iron]] |
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| [[Fluorite]], [[iron]], [[nickel]], [[heazlewoodite]] |
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|- |
|- |
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|style="text-align:center;"| 4–4.5 |
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| Ordinary [[steel]] |
| Ordinary [[steel]] |
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|- |
|- |
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|style="text-align:center;"| 4.5 |
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| [[Colemanite]] |
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| [[Conichalcite]], [[duftite]], [[colemanite]], [[lindgrenite]] |
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|- |
|- |
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| |
|style="text-align:center;"| 5 |
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| [[Apatite]] |
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| [[Apatite]], [[tooth enamel]], [[zirconium]], [[obsidian]] ([[volcanic glass]]) |
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|- |
|- |
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| |
|style="text-align:center;"| 5-5.5 |
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| [[Goethite]] |
| [[Goethite]] |
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|- |
|- |
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|style="text-align:center;"| 5.5 |
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| [[Glass]] |
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| [[Cobalt]], [[beryllium]], [[glass]], [[perovskite]], [[chromite]], [[bavenite]], [[agrellite]] |
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|- |
|- |
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| |
|style="text-align:center;"| 5.5–6 |
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| [[Opal]] |
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| [[Opal]], [[turquoise]], [[anatase]], [[arsenopyrite]]<ref name="geology.com" /> |
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|- |
|- |
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|style="text-align:center;"| 6 |
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| [[Rhodium]] |
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| [[Orthoclase|Orthoclase feldspar]], [[titanium]], [[uranium]], [[rhodium]] |
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|- |
|- |
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|style="text-align:center;"| 6-6.5 |
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| [[Rutile |
| [[Rutile]] |
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|- |
|- |
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|style="text-align:center;"| 6.5 |
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| [[Silicon]] |
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| [[Silicon]], [[iridium]], [[baddeleyite]], [[chloritoid]], [[berlinite]], [[cuprospinel]] |
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|- |
|- |
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|style="text-align:center;"| 6.5–7 |
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| [[ |
| [[Jadeite]] |
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|- |
|- |
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|style="text-align:center;"| 7 |
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| [[Porcelain]] |
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| [[Quartz]] (including [[amethyst]] and [[Quartz#Citrine|citrine]]), [[porcelain]], [[bowieite]] |
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|- |
|- |
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|style="text-align:center;"| 7-7.5 |
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| [[Garnet]] |
| [[Garnet]] |
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|- |
|- |
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|style="text-align:center;"| 7.5 |
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| [[Tungsten]] |
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| [[Tungsten]], [[zircon]], [[euclase]], [[hambergite]], [[grandidierite]] |
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|- |
|- |
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|style="text-align:center;"| 7.5–8 |
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| [[Emerald]] |
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| [[Beryl]] (including [[emerald]] and [[Aquamarine (gem)|aquamarine]]) |
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|- |
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|style="text-align:center;"| 8 |
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| [[Topaz]] |
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| ⚫ | |||
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|style="text-align:center;"| 8.5 |
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| [[Chromium]] |
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| [[Chromium]], [[silicon nitride]], [[tantalum carbide]], [[chrysoberyl]], [[tongbaite]] |
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|style="text-align:center;"| 9 |
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| [[Sapphire]] |
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| [[Corundum]] (including [[ruby]] and [[sapphire]]), [[tungsten carbide#Physical properties|tungsten carbide]], [[titanium nitride]] |
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|style="text-align:center;"| 9–9.5 |
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| [[Moissanite]] |
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| [[Moissanite]], [[silicon carbide]] (carborundum), [[tantalum carbide]], [[zirconium carbide]], [[beryllium carbide]], [[titanium carbide]], [[aluminium boride]], [[boron carbide]].<ref name=TedPellaMHT>{{cite web |title=Material hardness tables |website=www.tedpella.com |url=https://www.tedpella.com/company_html/hardness.htm |access-date=2019-05-09 |archive-date=2015-09-12 |archive-url=https://web.archive.org/web/20150912034606/https://www.tedpella.com/company_html/hardness.htm |url-status=dead }}</ref><ref name=PraterindustriesHT>{{cite web |title=Hardness table |url=https://www.praterindustries.com/wp-content/uploads/hardness-table.pdf |access-date=2019-05-09}}</ref> |
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|style="text-align:center;"| 9.5–near 10 |
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| [[Boron]] |
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| [[Boron]], [[boron nitride]], [[rhenium diboride]] (''a''-axis),<ref name=AFM>{{cite journal |last1=Levine |first1=Jonathan B. |last2=Tolbert |first2=Sarah H. |last3=Kaner |first3=Richard B. |year=2009 |title=Advancements in the search for superhard ultra-incompressible metal borides |journal=Advanced Functional Materials |volume=19 |issue=22 |pages=3526–3527 |doi=10.1002/adfm.200901257 |s2cid=98675890 |url=http://tolbert.chem.ucla.edu/Publication/AdvFuncMater-19-p3519.pdf |access-date=2015-12-08 |url-status=dead |archive-url=https://web.archive.org/web/20160304102359/http://tolbert.chem.ucla.edu/Publication/AdvFuncMater-19-p3519.pdf |archive-date=2016-03-04}}</ref> [[titanium diboride]], [[boron carbide]]<ref name="reade.com" /> |
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|style="text-align:center;"| 10 |
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| [[Diamond]] |
| [[Diamond]] |
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==Use== |
==Use== |
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Despite its lack of precision, the Mohs scale is relevant for field geologists, who use |
Despite its lack of precision, the Mohs scale is relevant for field geologists, who use it to roughly identify minerals using scratch kits. The Mohs scale hardness of minerals can be commonly found in reference sheets. |
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Mohs hardness is useful in [[Mill (grinding)|milling]]. It allows assessment of which type of mill and grinding medium will best reduce a given product whose hardness is known.<ref name="Milling1">{{cite web |title=Size reduction, comminution |series=Grinding and milling |publisher=PowderProcess.net |url=http://www.powderprocess.net/Grinding_Milling.html |access-date=27 October 2017}}</ref> |
Mohs hardness is useful in [[Mill (grinding)|milling]]. It allows the assessment of which type of mill and grinding medium will best reduce a given product whose hardness is known.<ref name="Milling1">{{cite web |title=Size reduction, comminution |series=Grinding and milling |publisher=PowderProcess.net |url=http://www.powderprocess.net/Grinding_Milling.html |access-date=27 October 2017}}</ref> |
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Electronic manufacturers use the scale for testing the resilience of flat panel display components (such as cover glass for [[Liquid-crystal display|LCD]]s or encapsulation for [[OLED]]s), as well as to evaluate the hardness of touch screens in consumer electronics.<ref>{{cite magazine |last=Purdy |first=Kevin |date=16 May 2014 |title=Hardness is not toughness: Why your phone's screen may not scratch, but will shatter |magazine=Computerworld |publisher=IDG Communications Inc. |url=https://www.computerworld.com/article/2833434/hardness-is-not-toughness--why-your-phone-s-screen-may-not-scratch--but-will-shatter.html |access-date=16 April 2021}}</ref> |
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== Comparison with Vickers scale == |
== Comparison with Vickers scale == |
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Comparison between Mohs hardness and [[Vickers hardness test|Vickers hardness]]:<ref name="mindat.org">{{cite web |last=Ralph |first=Jolyon |title=Welcome to mindat.org |website=mindat.org |publisher=Hudson Institute of Mineralogy |url=https://www.mindat.org/ |access-date=April 16, 2017}}</ref> |
Comparison between Mohs hardness and [[Vickers hardness test|Vickers hardness]]:<ref name="mindat.org">{{cite web |last=Ralph |first=Jolyon |title=Welcome to mindat.org |website=mindat.org |publisher=Hudson Institute of Mineralogy |url=https://www.mindat.org/ |access-date=April 16, 2017}}</ref> |
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{|class="wikitable" style="text-align:center" |
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! Mineral<br/>name |
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|[[Chromium]]||8.5||VHN{{sub|100}} = 1,875–2,000 |
|[[Chromium]]||8.5||VHN{{sub|100}} = 1,875–2,000 |
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==Footnotes== |
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{{notelist}} |
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==See also== |
==See also== |
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* [[Brinell scale]] |
* [[Brinell scale]] |
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* [[Geological Strength Index]] |
* [[Geological Strength Index]] |
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* [[Scratch hardness]] |
* [[Scratch hardness]] |
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* [[Superhard material]] |
* [[Superhard material]] |
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==References== |
==References== |
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==Further reading== |
==Further reading== |
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* {{cite magazine |last=Cordua |first=William S. |year=c. 1990 |title=The |
* {{cite magazine |last=Cordua |first=William S. |year=c. 1990 |title=The hardness of minerals and rocks |magazine=[[Lapidary Digest]] |url=http://www.gemcutters.org/LDA/hardness.htm |via=gemcutters.org }} |
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* {{Cite book |last=Raden |first=Aja |title=Gem: The |
* {{Cite book |last=Raden |first=Aja |year=2016 |title=Gem: The definitive visual guide |publisher=[[DK Publishing]] |isbn=9781465453563 |location=New York, NY |lang=en }} |
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{{Mohs}} |
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[[Category:Materials science]] |
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[[Category:Hardness tests]] |
[[Category:Hardness tests]] |
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[[Category:1812 in science]] |
[[Category:1812 in science]] |
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[[Category:1812 in |
[[Category:1812 in the Confederation of the Rhine]] |
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[[de:Härte#Härteprüfung nach Mohs]] |
[[de:Härte#Härteprüfung nach Mohs]] |
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Latest revision as of 13:43, 27 November 2024
The Mohs scale (/moʊz/ MOHZ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.
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 (English: Attempt at an elementary method for the natural-historical determination and recognition of fossils);[1][2][a] 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.[7]
Reference minerals
[edit]The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to visibly scratch another mineral. Minerals are chemically pure solids found in nature. Rocks are mixtures of one or more minerals.
Mohs scale along the horizontal axis matched with
one of the absolute hardness scales along the
vertical. Diamond (Mohs 10) is 1500 (off scale).
Diamond was the hardest known naturally occurring mineral when the scale was designed, and defines the top of the scale, arbitrarily set at 10. 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]
Technically, "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.[citation needed] The table below shows the comparison with the absolute hardness measured by a sclerometer, with images of the reference minerals in the rightmost column.[10][11]
Mohs
hardnessReference
mineralChemical formula Absolute
hardness[12]Example image 1 Talc Mg3Si4O10(OH)2 1 
2 Gypsum Ca SO4 · 2H2O 2 
3 Calcite Ca CO3 14 
4 Fluorite Ca F2 21 
5 Apatite Ca5(PO4)3 (OH−,Cl−,F−) 48 
6 Orthoclase
feldsparK Al Si3O8 72 
7 Quartz SiO2 100 
8 Topaz Al2SiO4(OH−,F−)2 200 
9 Corundum Al2O3 400 
10 Diamond C 1500 
Examples
[edit] | This section needs additional citations for verification. (November 2022) |
Below is a table of more materials by Mohs scale. Some of them have a hardness between two of the Mohs scale reference minerals. Some solid substances that are not minerals have been assigned a hardness on the Mohs scale. However, hardness can make it difficult to determine if the substance is a mixture of other substances or if it may be misleading or meaningless. For example, some sources have assigned a Mohs hardness of 6 or 7 to granite but it is a rock made of several minerals, each with its own Mohs hardness (e.g. topaz-rich granite contains: topaz — Mohs 8, quartz — Mohs 7, orthoclase — Mohs 6, plagioclase — Mohs 6–6.5, mica — Mohs 2–4).
Hardness Substance[13] 0.2–0.4 Potassium 0.5–0.6 Lithium 1 Talc 1.5 Lead 2 Hardwood[14] 2–2.5 Plastic 2.5 Zinc 2.5–3 Copper 3 Brass 3.5 Adamite 3.5-4 Sphalerite 4 Iron 4–4.5 Ordinary steel 4.5 Colemanite 5 Apatite 5-5.5 Goethite 5.5 Glass 5.5–6 Opal 6 Rhodium 6-6.5 Rutile 6.5 Silicon 6.5–7 Jadeite 7 Porcelain 7-7.5 Garnet 7.5 Tungsten 7.5–8 Emerald 8 Topaz 8.5 Chromium 9 Sapphire 9–9.5 Moissanite 9.5–near 10 Boron 10 Diamond
Use
[edit]Despite its lack of precision, the Mohs scale is relevant for field geologists, who use it 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 the assessment of which type of mill and grinding medium will best reduce a given product whose hardness is known.[15]
Electronic manufacturers use the scale 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.[16]
Comparison with Vickers scale
[edit]Comparison between Mohs hardness and Vickers hardness:[17]
Mineral
nameHardness (Mohs) Hardness (Vickers)
(kg/mm2)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 Goethite 5–5.5 VHN100 = 667 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
Footnotes
[edit]- ^
- 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. — von Groth (1926)
- 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.[1]
See also
[edit]References
[edit]- ^ a b 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.
- ^ "Mohs hardness". Encyclopædia Britannica (online ed.).
- ^ "Mohs scale of hardness". Mineralogical Society of America. Retrieved 10 February 2021.
- ^ Theophrastus. Theophrastus on Stones. Retrieved 10 December 2011 – 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 14 February 2014.
- ^ "Mohs scale of mineral hardness". American Federation of Mineralogical Societies – via amfed.org.
- ^ Geels, Kay (26 April 2000). "The true microstructure of materials". Materialographic Preparation from Sorby to the Present (PDF). Application notes and guides (Report). The Struers metallographic library. Copenhagen, DK: Struers A/S. pp. 5–13. Archived from the original (PDF) on 7 March 2016.
- ^ "What is important about hardness?". Amethyst galleries. Mineral gallery. Archived from the original on 30 December 2006 – via galleries.com.
- ^ "Mineral hardness and hardness scales". Inland Lapidary. Archived from the original on 17 October 2008 – via inlandlapidary.com.
- ^ Mukherjee, Swapna (2012). Applied Mineralogy: Applications in industry and environment. Springer Science & Business Media. p. 373. ISBN 978-94-007-1162-4 – via Google books.
- ^ Samsonov, G.V., ed. (1968). "Mechanical properties of the elements". Handbook of the Physicochemical Properties of the Elements. New York, NY: IFI-Plenum. p. 432. doi:10.1007/978-1-4684-6066-7. ISBN 978-1-4684-6068-1.
- ^ "Mohs Hardness Scale: Testing the Resistance to Being Scratched". geology.com. Retrieved 9 August 2021.
- ^ "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 16 April 2017.
Further reading
[edit]- Cordua, William S. (c. 1990). "The hardness of minerals and rocks". Lapidary Digest – via gemcutters.org.
- Raden, Aja (2016). Gem: The definitive visual guide. New York, NY: DK Publishing. ISBN 9781465453563.
