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The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch hardness of through the ability of harder material to scratch softer material.
The scale was introduced in 1812 by the German geologist and Mineralogy Friedrich Mohs, in his book Versuch einer Elementar-Methode zur naturhistorischen Bestimmung und Erkennung der Fossilien (English: 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.
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 research, but is not an accurate predictor of how well materials endure in an industrial setting.
| Mohs scale along the horizontal axis matched with one of the absolute hardness scales along the vertical. Vertical scale is logarithmic. |
Technically, "scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Frequently, materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number. While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number.
Each of the ten hardness values in the Mohs scale is represented by a reference mineral, most of which are widespread in rocks.
The Mohs scale is an ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is four times as hard as corundum. The table below shows the comparison with the absolute hardness measured by a sclerometer, with images of the reference minerals in the rightmost column.
| 1 | Talc | 1 | ||
| 2 | Gypsum | 2 | ||
| 3 | Calcite | 14 | ||
| 4 | Fluorite | 21 | ||
| 5 | Apatite | 48 | ||
| 6 | Orthoclase | 72 | ||
| 7 | Quartz | 100 | ||
| 8 | Topaz | 200 | ||
| 9 | Corundum | 400 | ||
| 10 | Diamond | 1500 |
| 0.2–0.4 | Potassium (1968). 9781468460681, IFI-Plenum. ISBN 9781468460681 |
| 0.5–0.6 | Lithium |
| 1 | Talc |
| 1.5 | Lead |
| 2 | Hardwood |
| 2–2.5 | Plastic |
| 2.5 | Zinc |
| 2.5–3 | Native copper |
| 3 | Brass |
| 3.5 | Adamite |
| 3.5–4 | Sphalerite |
| 4 | Iron |
| 4–4.5 | Ordinary steel |
| 4.5 | Colemanite |
| 5 | Apatite |
| 5–5.5 | Goethite |
| 5.5 | Glass |
| 5.5–6 | Opal |
| 6 | Rhodium |
| 6–6.5 | Rutile |
| 6.5 | Silicon |
| 6.5–7 | Jadeite |
| 7 | Porcelain |
| 7–7.5 | Garnet |
| 7.5 | Tungsten |
| 7.5–8 | Emerald |
| 8 | Topaz |
| 8.5 | Chromium |
| 9 | Sapphire |
| 9–9.5 | Moissanite |
| 9.5–near 10 | Boron |
| 10 | Diamond |
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 (such as cover glass for LCDs or encapsulation for ), as well as to evaluate the hardness of touch screens in consumer electronics.
| VHN = 7–9 |
| VHN = 16–18 |
| VHN = 30–34 |
| VHN = 61–65 |
| VHN = 84–87 |
| VHN = 77–99 |
| VHN = 79–104 |
| VHN = 208–224 |
| VHN = 230–254 |
| VHN = 667 |
| VHN = 1,278–1,456 |
| VHN = 616–698 |
| VHN = 894–974 |
| VHN = 1,505–1,520 |
| VHN = 858–1,288 |
| VHN = 1,310 |
| VHN = 1,875–2,000 |
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