Mohs scale
The Mohs scale 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 ; it is one of several definitions of hardness in materials science, some of which are more quantitative.
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,, followed by Pliny the Elder in his Naturalis Historia,. 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.
Examples
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. Hardness may be difficult to determine, or may be misleading or meaningless, if a material is a mixture of multiple substances. For example, granite has been assigned by some sources a Mohs hardness between 6 and 7, but it is a rock made of several minerals, each with its own Mohs hardness. Topaz-rich granite is mainly composed of topaz, quartz, orthoclase, plagioclase, and mica.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.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.
Electronic manufacturers use the scale for testing the resilience of flat panel display components, as well as to evaluate the hardness of touch screens in consumer electronics.