Mohs scale of mineral hardness

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Mohs scale of mineral hardness

Not to be confused with mhos
Siemens (unit)

The siemens is the SI SI derived unit of electric conductance. It is equal to inverse ohm. It is named after the Germany inventor and industrialist Ernst Werner von Siemens, and was previously called the #Mho....
, a unit of electric conductance.

The Mohs scale of mineral hardness characterizes the scratch resistance of various mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s through the ability of a harder material to scratch a softer material. It was created in 1812 by the German mineralogist

Mineralogy

Mineralogy is an Earth Science focused around the chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization....
Friedrich Mohs

Friedrich Mohs

Friedrich Mohs was a Germany geologist/mineralogist....
and is one of several definitions of hardness in materials science

Materials science

Materials science or materials engineering is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering....
. The method, however, is of great antiquity, having first been mentioned by Theophrastus

Theophrastus

Theophrastus , a Greek native of Eressos in Lesbos Island, was the successor of Aristotle in the Peripatetic school. His interests were wide-ranging, extending from biology and physics to ethics and metaphysics....
in his treatise On Stones in ca 300 BC, followed by Pliny the Elder

Pliny the Elder

Gaius Plinius Secundus , better known as Pliny the Elder, was an ancient author, naturalist or natural philosopher and naval and military commander of some importance who wrote Natural History ....
in his Naturalis Historia

Naturalis Historia

Naturalis Historia is an encyclopedia written circa AD 77 by Pliny the Elder. It is one of the largest single works to have survived from the Roman empire to the modern day, and was one of the first reference works developed in the Classical period to examine natural and man-made objects, both organic and mineral, as well as many natura...
circa A.D.

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Encyclopedia

Mineral

Mineralogy

Friedrich Mohs

Friedrich Mohs was a Germany geologist/mineralogist....
and is one of several definitions of hardness in materials science

Materials science

Theophrastus

Pliny the Elder

Naturalis Historia

Minerals

Mohs based the scale on ten minerals that are all readily available. As the hardest known naturally occurring substance, diamond

Diamond

In mineralogy, diamond is the Allotropes of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. After graphite, diamond is the second most stable form of carbon....
is 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.

The Mohs scale is a purely ordinal

Level of measurement

The "levels of measurement" is an expression which typically refers to the theory of scale types developed by the Harvard psychologist Stanley Smith Stevens....
scale. For example, corundum

Corundum

Corundum is a crystalline form of aluminium oxide and is one of the rock -forming minerals. It is naturally clear, but can have different colors when impurities are present....
(9) is twice as hard as topaz

Topaz

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula aluminium2siliconoxygen42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present....
(8), but diamond (10) is almost four times as hard as corundum. The table below shows comparison with absolute hardness measured by a sclerometer

Sclerometer

The sclerometer, also known as the Turner-sclerometer , is an instrument used by mineralogists to measure the scratch hardness of materials....
, with pictorial examples.

Mohs hardness	Mineral	Absolute Hardness
1	Talc Talc Talc is a mineral composed of hydrated magnesium silicate with the chemical formula Hydrogen2Magnesium34 or Magnesium3Silicon4Oxygen102.... (Mg₃Si₄O₁₀(OH)₂)	1
2	Gypsum Gypsum Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula calciumsulfuroxygen4?2water.... (CaSO₄·2H₂O)	3
3	Calcite Calcite Calcite is a Carbonate minerals and the most stable Polymorphism of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite.... (CaCO₃)	9
4	Fluorite Fluorite Fluorite is a mineral composed of calcium fluoride, CalciumFluorine. It is an Cubic mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon.... (CaF₂)	21
5	Apatite Apatite Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of Hydroxyl−, Fluorine−, or Chlorine− ions, respectively, in the crystal.... (Ca₅(PO₄)₃(OH-,Cl-,F-)	48
6	Feldspar Feldspar Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's Crust .Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock.... (KAlSi₃O₈)	72
7	Quartz Quartz Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?.... (SiO₂)	100
8	Topaz Topaz Topaz is a silicate mineral of aluminium and fluorine with the chemical formula aluminium2siliconoxygen42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present.... (Al₂SiO₄(OH-,F-)₂)	200
9	Corundum Corundum Corundum is a crystalline form of aluminium oxide and is one of the rock -forming minerals. It is naturally clear, but can have different colors when impurities are present.... (Al₂O₃)	400
10	Diamond Diamond In mineralogy, diamond is the Allotropes of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. After graphite, diamond is the second most stable form of carbon.... (C)	1600

On the Mohs scale, a pencil "lead" (graphite

Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
) has a hardness of 1; a fingernail, 2.5; a copper penny, about 3.5; a knife blade, 5.5; window glass, 5.5; and a steel file

File (tool)

A file is a hand tool used to shape material by cutting. A file typically takes the form of a hardened steel bar, mostly covered with a series of sharp, parallel ridges or teeth....
, 6.5. 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
1	Talc Talc Talc is a mineral composed of hydrated magnesium silicate with the chemical formula Hydrogen2Magnesium34 or Magnesium3Silicon4Oxygen102.... , graphite Graphite The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
2.5 to 3	Pure gold Gold Gold is a chemical element with the symbol Au and atomic number 79. It is a highly sought-after precious metal, having been used as money, as a store of value, in jewelry, in sculpture, and for ornamentation since the beginning of recorded history.... , silver Silver Silver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal.... , aluminium Aluminium Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
3	Calcite Calcite Calcite is a Carbonate minerals and the most stable Polymorphism of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite.... , copper Copper Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....
4	Fluorite Fluorite Fluorite is a mineral composed of calcium fluoride, CalciumFluorine. It is an Cubic mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon....
4 to 4.5	Platinum Platinum Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements....
4 to 5	Steel Steel Steel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.14% by weight , depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten....
5	Apatite Apatite Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of Hydroxyl−, Fluorine−, or Chlorine− ions, respectively, in the crystal....
6	Orthoclase Orthoclase Orthoclase is an important Silicate minerals mineral which forms igneous rocks. The name is from the Greek language for "straight fracture," because its two cleavage planes are at right angles to each other....
6	Titanium Titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the ?space age metal?, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver colour....
6.5	Iron pyrite
6 to 7	Glass Glass Glass generally refers to a Hardness, brittle, transparency amorphous solid, such as that used for windows, many Glass Bottles, or eyewear, including, but not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovite , or aluminium oxynitride.... , fused quartz Fused quartz Fused quartz and fused silica are types of glass containing primarily silica in amorphous solid form. They are manufactured using several different processes....
7	Quartz Quartz Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
7 to 7.5	Garnet Garnet The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" comes from the Latin language granatus , possibly a reference to the Punica granatum , a plant with red seeds similar in shape, size, and color to some garnet crystals....
7 to 8	Hardened steel Hardened steel The term hardened steel is often used for a plain-carbon steel steel that has been given the heat treatments of quenching followed by tempering....
7.5	Tungsten Tungsten Tungsten , also known as wolfram , is a chemical element that has the symbol W and atomic number 74.A steel-gray metal, tungsten is found in several ores, including wolframite and scheelite....
8	Topaz Topaz Topaz is a silicate mineral of aluminium and fluorine with the chemical formula aluminium2siliconoxygen42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present....
8.5	Chrysoberyl Chrysoberyl The mineral or gemstone chrysoberyl, not to be confused with beryl, is an aluminium of beryllium with the formula BeAl2O4.... , chromium Chromium Chromium is a chemical element which has the symbol Cr and atomic number 24. It is a steely-gray, Lustre , hard metal that takes a high polish and has a high melting point....
8.5 to 9	Tungsten carbide Tungsten carbide Tungsten carbide, WC, or tungsten semicarbide, W2C, is a chemical compound containing tungsten and carbon, similar to titanium carbide....
9	Corundum Corundum Corundum is a crystalline form of aluminium oxide and is one of the rock -forming minerals. It is naturally clear, but can have different colors when impurities are present....
9 to 9.5	Carborundum
<10	Ultra-hard fullerite
10	Diamond Diamond In mineralogy, diamond is the Allotropes of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. After graphite, diamond is the second most stable form of carbon....
>10	Aggregated diamond nanorods Aggregated diamond nanorods Aggregated diamond nanorods, or ADNRs , is a nanocrystalline form of diamond believed to be the Hardness and least compressible known material, as measured by its isothermal bulk modulus; aggregated diamond nanorods have a modulus of 491 gigapascals , while a conventional diamond has a modulus of 442 GPa.... , Rhenium diboride Rhenium diboride Rhenium diboride is a synthetic superhard material. It was discovered by a team at University of California, Los Angeles and announced in Science in April 2007....

Mohs scale of mineral hardness

Minerals

Intermediate hardness

See also