Mohs scale

The Mohs scale is the approximate measure of the resistance that a smooth surface has to scratching or abrasion, expressed in terms of a scale devised by the German mineralogist Friedrich Mohs, a German scientist and geologist in the year 1773 who dedicated himself to studying chemistry , mathematics and physics . The scale of a mineral is determined by observing whether its surface is scratched by a substance of known or defined hardness. Sort then the hardness of minerals according to the ability that they have to be scratched and is sorted so ascending , where the number one is classified as ore more soft talc or and number ten as the diamond hard .

What is the Mohs scale?

The Mohs scale is an empirical table that is used to determine the hardness of a mineral by making comparisons with others that are considered as standards . Has 10 different minerals reference and the hardness is determined by making samples of striped .

  • What is the Mohs scale?
  • What is the Mohs scale for?
  • Mohs hardness
  • Other scales
  • Examples

What is the Mohs scale?

To give numerical values to the physical property of minerals, they are classified along the Mohs scale, which is made up of 10 minerals that have been given arbitrary hardness values . The minerals contained in the scale are shown in the table; while at the same time other materials are shown that approximate the hardness of some of the minerals.

During the determination procedure, it is necessary to be sure that a scratch that has been made is really well done and marked and that it is not just a small mark that will be easily erased. If the species being tested is fine grained the test can only loosen the grains without examining the individual mineral surfaces ; therefore, certain added textures or shapes can hinder or prevent a true determination of hardness .

The scale is based on ten minerals that are very easy to get and basically the minerals are compared to determine which of them is the hardest. The hardness of a material is then measured according to the scale to find the hardest material or the softest material that can scratch the given material. The Mohs scale is as follows:

HardnessMaterialAbsolute Hardness
1Talc (Mg3Si4O10 (OH) 2)1
2Gypsum (CaSO4 · 2H2O)3
3Calcite (CaCO3)9
4Fluorite (CaF2)twenty-one
5Apatite (Ca5 (PO4) 3 (OH-, Cl-, F-))48
6Orthoclase (KAlSi3O8)72
7Quartz (SiO2)100
8Topaz (Al2SiO4 (OH-, F-) 2)200
9Corundum (Al2O3)400
10Diamond (C)1500

What is the Mohs scale for?

The Mohs scale is basically a table that is used to determine the hardness of minerals by classifying them according to physical characteristics , specifically by the hardness they present. Through it we can classify and make measurements of the difficulty that a certain mineral has to be scratched or to undergo any type of alteration in its structure, taking into account that it is not the same as breaking said material.

Mohs hardness

The relative value of the hardness that a mineral has can be calculated when it is compared with another, whose hardness is known. This way of measuring minerals was made by Mohs in a very simple way which is still applied today, always following certain rules . It should be remembered that in order to determine the hardness of the mineral, it must be related to the resistance it has to be able to be scratched or not.

Mohs hardness is a very simple comparative test , but at the same time it is a bit inaccurate . Perhaps its simplicity has allowed it to become the most widely used hardness test .

Despite its simplicity and lack of precision , the Mohs scale is very relevant to geologists in the field , who use it to identify minerals using kits from scratch . The Mohs scale hardness of minerals can be commonly found on reference sheets .

Other scales

Since the Mohs scale was developed in the year 1812, other tests have been invented to measure the hardness of minerals. These tests include, for example, the Brinell , Knoop , Rockwell , Shore, and Vickers tests . Each of these tests uses a small ” penetrator ” that is applied to the material with a carefully measured amount of force . Next, the size or depth of the sign and the amount of force that was used are used to calculate the hardness value .

Because each of these tests uses a different apparatus and different calculations , they cannot be directly compared to each other. So if the Knoop hardness test was performed, the number is usually reported as a ‘ Knoop hardness ‘ . It is for this reason that the results of the Mohs hardness test should also be reported as a ” Mohs hardness “.

Although these tests are quite different from the Mohs test, there is some correlation between them.


Some examples of the Mohs scale are as follows:

  • Most of the gems have a hardness of 7 or more, although some of them are very inferior such as turquoise with 5, feldspar with 6 and amazonite .
  • Goethite, Natrolite, Datolite, Analcime, Wollastonite with a degree of hardness of 5.
  • The sulfur has a hardness of 2, molybdenite 1.5 and auricalcita 1.

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