The Mohs scale is a 10-point scale created by Carl Friedrich Mohs in 1812 that allows comparison of the hardness of minerals. The scale gives a qualitative, not a quantitative assessment of the hardness of a particular stone.
History of Creation
To create the scale, Mohs used 10 reference minerals - talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, red corundum and diamond. He arranged the minerals in order of increasing hardness, taking as a starting point that a harder mineral scratches a softer one. Calcite, for example, scratches gypsum, and fluorite leaves scratches on calcite, and all these minerals cause talc to crumble. So the minerals received the corresponding hardness values in the Mohs scale: chalk -1, gypsum - 2, calcite - 3, fluorite - 4. Further studies showed that minerals whose hardness is below 6 are scratched by glass, those whose hardness is above 6 scratch glass. The hardness of glass on this scale is approximately 6.5.
Stones with a hardness greater than 6 are cut with diamond.
Mohs scaleis intended only for a rough assessment of the hardness of minerals. A more accurate indicator is absolute hardness.
The location of minerals in the Mohs scale
Minerals in the scale are arranged in order of hardness. The softest has a hardness of 1, scratches with a fingernail, for example, talc (chalk). Next come some harder minerals - ulexite, amber, muscovite. Their hardness on the Mohs scale is low - 2. Such soft minerals are not polished, which limits their use in jewelry. Beautiful stones with low hardness are ornamental, and are usually inexpensive. Souvenirs are often made from them.
Minerals with a hardness of 3 to 5 are easily scratched with a knife. Jet, rhodochrosite, malachite, rhodonite, turquoise, jade are often cut cabochon, well polished (usually using zinc oxide). These minerals are not resistant to water.
Hard jewelry minerals, diamonds, rubies, emeralds, sapphires, topazes and garnets, are processed depending on transparency, color, presence of impurities. Star-shaped rubies or sapphires, for example, are cut cabochons to emphasize the unusualness of the stone, transparent varieties are cut in ovals, circles or drops, like diamonds.
| Mohs hardness | Examples of minerals |
| 1 | Talc, graphite |
| 2 | Ulexite, muscovite, amber |
| 3 | Biotite, chrysocolla, jet |
| 4 | Rhodochrosite, fluorite, malachite |
| 5 | Turquoise, rhodonite, lapis lazuli, obsidian |
| 6 | Benitoite, larimar, moonstone, opal, hematite, amazonite, labradorite |
| 7 | Amethyst, garnet, varieties of tourmaline indicolite, verdelite, rubellite, schorl), morion, agate, aventurine, citrine |
| 8 | Green corundum (emerald), heliodor, topaz, painite, taaffeite |
| 9 | Red corundum (ruby), blue corundum (sapphire), leucosapphire |
| 10 | Diamond |
Gemstones
All minerals with a hardness less than 7 are considered soft, those above 7 are considered hard. Hard minerals can be cut with diamonds, the variety of possible cuts, transparency and rarity make them ideal for use in jewelry.
The hardness of a diamond on the Mohs scale is 10. Diamonds are faceted in such a way that the loss in stone mass during processing is minimal. A cut diamond is called a diamond. Due to their high hardness and resistance to high temperatures, diamonds are virtually eternal.
The hardness of ruby and sapphire is slightly lower than the hardness of diamond and is 9 on the Mohs scale. The value of these stones, as well as emeralds, depends on the color, transparency and number of defects - the more transparent the stone, the more intense the color and the fewer cracks in it, the higher the price.
Semi-precious stones
Slightly lower than diamond and corundum, topazes and garnets are valued. Their hardness on the Mohs scale is7-8 points. These stones lend themselves well to diamond cutting. The price directly depends on the color. The richer the color of topaz or garnet, the more expensive the product with it will cost. The most highly valued are the extremely rare yellow topazes and purple garnets (majorites). The final stone is so rare that it could be worth more than a pure diamond.
Colored tourmalines: pink (rubellite), blue (indicolite), green (verdelite), watermelon tourmaline are also classified as semi-precious stones. High-quality transparent tourmalines are very rare in nature, which is why they are sometimes much more expensive than pyropes and blue topazes, and collectors do not get tired of hunting for watermelon (pink-green) stones. The hardness of stones on the Mohs scale is quite high and is 7-7.5 points. These stones lend themselves well to polishing, do not change color, and finding a piece of jewelry with a bright transparent tourmaline is a real success.
The black variety of tourmaline (shorl) belongs to ornamental stones. Schorl is a hard but brittle stone that can easily break during processing. It is for this reason that black tourmalines are most often sold raw. Sherl is considered the strongest protective talisman.
Industrial applications
Minerals and rocks with high hardness are widely used in industry. For example, the hardness of granite on the Mohs scale is from 5 to 7, depending on the amount of mica in it. This hard rock is widely used in construction as a finishing material.
Colorless sapphires or leucosapphires, despite their high hardness and relative rarity, are not in demand among jewelers, but are widely used in laser and other optical installations.
Practical application of the scale
Despite the fact that the Mohs hardness scale gives only a qualitative, not a quantitative assessment, it is widely used in geology. Using the Mohs scale, geologists and mineralogists can roughly identify an unknown rock based on its susceptibility to scratching with a knife or glass. Almost all reference sources indicate the hardness of minerals on the Mohs scale, and not their absolute hardness.
In jewelry, the Mohs scale is also widely used. The hardness of the stone determines the method of its processing, possible grinding options and the tools necessary for this.
Other hardness scales
The Mohs scale is not the only hardness scale. There are several other scales based on the ability of minerals and other materials to resist deformation. The most famous of these is the Rockwell scale. The Rockwell method is simple - it is based on measuring the depth of penetration of the identer deep into the material under study. A diamond tip is usually used as an identifier. It is worth noting that minerals are rarely examined by the Rockwell method, it is usually used for metals and alloys.
Short hardness scales are built in a similar way. The Shore method allows you to determine the hardness of both metals and more elasticmaterials (rubber, plastic).
