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From Latin duritĭa, is defined as hardness to hard quality . For example: “The hardness of this mattress is quite annoying”, "Leather pants have a very particular hardness that makes them somewhat uncomfortable".

Hardness is also a callosity or tumor that may appear in different parts of the body : “My elbows have all kinds of hardness although I try to rub myself when I take a shower”, “I have detected a hardness in my leg that worries me”, “When performing the body exam, no hardness should appear”.

In the same way, we must not forget that there is what is known as belly hardness. This is an expression used in the field of biology to be able to refer to the difficulty that a being has to carry out what would be the stool evacuation.

For the geology , the hardness is the resistance that one mineral opposes being scratched by another. It is, therefore, a mechanical property of minerals. There is also talk of hardness with respect to the penetrability of a surface to refer to the possibility of making marks with a tip.

In this sense we have to make it clear that throughout the history various classifications of minerals have been established and fundamentally based on the aforementioned hardness. Hence we find, for example, the well-known Rosiwal scale, which is named after the Austrian geologist who gives it its name: August Karl Rosiwal.

In the period between the end of the 19th century and the beginning of the 20th century it was when he undertook the creation of one that is based on absolute values ​​and that determines that in the degree of hardness 1 the talc is found, in 2 the plaster, in 3 Calcite ... The maximum hardness level, 10, lies with the diamond.

In the same way, another of the most relevant scales in this regard is the Mohs scale, created in 1825 by the German Friedich Mohs and based on a list of ten minerals that are ordered from least to greatest hardness. With it it is also clear that each of them can be scratched by minerals that have a number equal to or greater than theirs while he can scratch those that are one point below.

The metallurgical industry uses a hardness tester to measure hardness during penetration tests. These tests consist of the use of different types of tips and the application of various loads to analyze the marks made. From these tests, different scales are established.

The determination of the hardness of a steel allows the correlation between hardness and mechanical strength to be established. There are several machines that allow these measurements to be made and that are of great importance in industrial activity.

Finally, in a symbolic or metaphorical sense, the notion of hardness is used to refer to something difficult or complex : "The rally is a test of great hardness for competitors", "The hardness of the challenge is undeniable".

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