Carl Friedrich Christian Mohs (/moʊz/ MOHZ, German: [ˈfʁiːdʁɪç ˈmoːs]; 29 January 1773 – 29 September 1839) was a German chemist and mineralogist. He was the creator of the Mohs scale of mineral hardness. Mohs also introduced a classification of the crystal forms in crystal systems independently of Christian Samuel Weiss.
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 (transl. Attempt at an elementary method for the natural-historical determination and recognition of fossils); it is one of several definitions of hardness in materials science, some of which are more quantitative.
Scratch hardness refers to the hardness of a material in terms of resistance to scratches and abrasion by a harder material forcefully drawn over its surface. Scratch hardness test or scratch test refers to any of a number of methods of measuring scratch hardness. Resistance to abrasion is less affected by surface variations than indentation methods. Scratch hardness is measured with a sclerometer.
Attempting to scratch a surface to test a material is a very old technique. The first scientific attempt to quantify materials by scratch tests was by mineralogist Friedrich Mohs in 1812 (see Mohs scale). The Mohs scale is based on relative scratch hardness of different materials; with talc assigned a value of 1 and diamond assigned a value of 10. Mohs's scale had two limitations: it was not linear, and most modern abrasives fall between 9 and 10.; so, later scientists attempted to increase resolution at the harder end of the scale.