Mohs scale of mineral hardness - wikipedia Mohs scale of mineral hardness Mohs hardness kit, containing one specimen of each mineral on the ten - point hardness scale The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, some of which are more quantitative. The method of comparing hardness by seeing which minerals can visibly scratch others is, however, 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. 77 AD. While greatly facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Contents 1 Usage 2 Minerals 3 Intermediate hardness 4 Comparison with Vickers scale 5 See also 6 References 7 Further reading Usage Despite its lack of precision, the Mohs scale is highly 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. 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 pure substances 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 fall between 4 and 5. `` 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. 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 the comparison with the absolute hardness measured by a sclerometer, with pictorial examples. Mohs hardness Mineral Chemical formula Absolute hardness Image Talc Mg Si O ( OH ) Gypsum CaSO 2H O Calcite CaCO 9 Fluorite CaF 21 5 Apatite Ca ( PO ) ( OH, Cl, F ) 48 6 Orthoclase feldspar KAlSi O 72 7 Quartz SiO 100 8 Topaz Al SiO ( OH, F ) 200 9 Corundum Al O 400 10 Diamond 1500 On the Mohs scale, a streak plate ( unglazed porcelain ) has a hardness of approximately 7.0. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. 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 talc 1.5 gallium, strontium, indium, tin, barium, thallium, lead, graphite, ice hexagonal boron nitride, calcium, selenium, cadmium, sulfur, tellurium, bismuth, gypsum 2 -- 2.5 halite ( rock salt ) 2.5 -- 3 gold, silver, aluminium, zinc, lanthanum, cerium, Jet ( lignite ) calcite, copper, arsenic, antimony, thorium, dentin 3.5 platinum fluorite, iron, nickel 4 -- 4.5 steel 5 apatite ( tooth enamel ), zirconium, palladium, obsidian ( volcanic glass ) 5.5 beryllium, molybdenum, hafnium, glass, cobalt 6 orthoclase, titanium, manganese, germanium, niobium, rhodium, uranium 6 -- 7 fused quartz, iron pyrite, silicon, ruthenium, iridium, tantalum, opal, peridot, tanzanite, jade 7 osmium, quartz, rhenium, vanadium 7.5 -- 8 emerald, hardened steel, tungsten, spinel 8 topaz, cubic zirconia 8.5 chrysoberyl, chromium, silicon nitride, tantalum carbide 9 corundum, tungsten carbide, titanium nitride 9 -- 9.5 silicon carbide ( carborundum ), titanium carbide 9.5 -- 10 boron, boron nitride, rhenium diboride ( a-axis ), stishovite, titanium diboride 10 diamond, carbonado > 11 nanocrystalline diamond ( hyperdiamond, ultrahard fullerite ), rhenium diboride ( c - axis ) Comparison with vickers scale This list is incomplete ; you can help by expanding it. Comparison between hardness ( Mohs ) and hardness ( Vickers ) : Mineral name Hardness ( Mohs ) Hardness ( Vickers ) kg / mm Graphite 1 -- 2 VHN = 7 -- 11 Tin 11⁄2 VHN = 7 -- 9 Bismuth 2 -- 21⁄2 VHN = 16 -- 18 Gold 21⁄2 VHN = 30 -- 34 Silver 21⁄2 VHN = 61 -- 65 Chalcocite 21⁄2 -- 3 VHN = 84 -- 87 Copper 21⁄2 -- 3 VHN = 77 -- 99 Galena 21⁄2 VHN = 79 -- 104 Sphalerite 31⁄2 -- 4 VHN = 208 -- 224 Heazlewoodite VHN = 230 -- 254 Carrollite 41⁄2 -- 51⁄2 VHN = 507 -- 586 Goethite 5 -- 51⁄2 VHN = 667 Hematite 5 -- 6 VHN = 1,000 -- 1,100 Chromite 51⁄2 VHN = 1,278 -- 1,456 Anatase 51⁄2 -- 6 VHN = 616 -- 698 Rutile 6 -- 61⁄2 VHN = 894 -- 974 Pyrite 6 -- 61⁄2 VHN = 1,505 -- 1,520 Bowieite 7 VHN = 858 -- 1,288 Euclase 71⁄2 VHN = 1,310 Chromium 81⁄2 VHN = 1,875 -- 2,000 See also Brinell scale Hardnesses of the elements ( data page ) Knoop hardness test Meyer hardness test Pencil hardness Rockwell scale Scratch hardness References ^ Jump up to : `` Mohs hardness '' in Encyclopædia Britannica Online Jump up ^ Theophrastus on Stones. Farlang.com. Retrieved on 2011 - 12 - 10. Jump up ^ Pliny the Elder. Naturalis Historia. Book 37. Chap. 15. ADamas : six varieties of it. Two remedies. Jump up ^ Pliny the Elder. Naturalis Historia. Book 37. Chap. 76. The methods of testing precious stones. Jump up ^ Hardness. Non-Destructive Testing Resource Center Jump up ^ `` Size reduction, comminution - grinding and milling ''. PowderProcess.net. Retrieved 27 October 2017. Jump up ^ Learn science, Intermediate p. 42 Jump up ^ American Federation of Mineralogical Societies. `` Mohs Scale of Mineral Hardness ''. amfed.org Jump up ^ Geels, Kay. `` The True Microstructure of Materials '', pp. 5 -- 13 in Materialographic Preparation from Sorby to the Present. Struers A / S, Copenhagen, Denmark Jump up ^ Amethyst Galleries ' Mineral Gallery What is important about hardness ?. galleries.com Jump up ^ Mineral Hardness and Hardness Scales Archived 2008 - 10 - 17 at the Wayback Machine... Inland Lapidary Jump up ^ Mukherjee, Swapna ( 2012 ). Applied Mineralogy : Applications in Industry and Environment. Springer Science & Business Media. pp. 373 --. ISBN 978 - 94 - 007 - 1162 - 4. Jump up ^ 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. Jump up ^ `` Ice is a mineral '' in Exploring Ice in the Solar System. messenger-education.org Jump up ^ Berger, Lev I. ( 1996 ). Semiconductor Materials ( First ed. ). Boca Raton, FL : CRC Press. p. 126. ISBN 978 - 0849389122. ^ Jump up to : Levine, Jonathan B. ; Tolbert, Sarah H. ; Kaner, Richard B. ( 2009 ). `` Advancements in the Search for Superhard Ultra-Incompressible Metal Borides '' ( PDF ). Advanced Functional Materials. pp. 3526 -- 3527. doi : 10.1002 / adfm. 200901257. Jump up ^ Ralph, Jolyon. `` Welcome to mindat.org ''. mindat.org. Hudson Institute of Mineralogy. Retrieved April 16, 2017. Further reading 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 Cleavage Crystal habit Crystal system Fracture Lustre Mohs scale Specific gravity Streak Retrieved from `` https://en.wikipedia.org/w/index.php?title=Mohs_scale_of_mineral_hardness&oldid=824963630 '' Categories : Materials science Mineralogy Hardness tests 1812 in science Hidden categories : Webarchive template wayback links All articles lacking reliable references Articles lacking reliable references from January 2018 Incomplete lists from August 2017 Wikipedia articles needing factual verification from August 2017 Pages using div col without cols and colwidth parameters Talk Contents About Wikipedia Afrikaans Aragonés বাংলা Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Català Čeština Cymraeg Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Galego 한국어 Հայերեն Hrvatski Bahasa Indonesia Íslenska Italiano עברית Basa Jawa ქართული Latviešu Lietuvių Magyar Македонски മലയാളം Bahasa Melayu Монгол Nederlands 日本 語 Norsk Norsk nynorsk Occitan پنجابی پښتو Plattdüütsch Polski Português Română Русский Саха тыла Scots Shqip Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska தமிழ் ไทย Türkçe Українська اردو Tiếng Việt 中文 Edit links This page was last edited on 10 February 2018, at 17 : 30. 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Question: how hard is graphite on the mohs scale
Answer: 1.5