Mohs scale - a 10-point scale created by Karl Friedrich Moos in 1812, which allows you to compare the hardness of minerals. The scale gives a qualitative, not quantitative assessment of the hardness of a particular stone.
History of creation
To create the scale, Moos used 10 reference minerals - talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, red corundum and diamond. He placed the minerals in increasing order of their 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 minerals obtained the corresponding values of hardness in the Mohs scale: chalk -1, gypsum - 2, calcite - 3, fluorite - 4. Further studies showed that minerals with a hardness below 6 are scratched by glass, those with a hardness above 6 - scratch the glass . The hardness of glass on this scale is approximately 6.5.
Stones with a hardness of more than 6 are processed with diamond.
The Mohs scale is intended only for a rough estimate of the hardness of minerals. A more accurate indicator is absolute hardness.
The location of the minerals in the Mohs scale
Minerals in the scale are arranged in order of hardness. The softest one has a hardness of 1, it is scratched with a fingernail, for example, talc (chalk). Next are several harder minerals - ulexite, amber, muscovite. Their hardness on the Mohs scale is small - 2. Such soft minerals are not polished, which limits their use in jewelry. Beautiful stones with low hardness are semi-precious, and are usually inexpensive. Often, souvenirs are often made.
Minerals with a hardness of 3 to 5 are easily scratched with a knife. Jet, rhodochrosite, malachite, rhodonite, turquoise, jade are often sanded with cabochon, well polished (usually using zinc oxide). These minerals are not resistant to water.
Solid jewelry minerals, diamonds, rubies, emeralds, sapphires, topazes and garnets are processed depending on transparency, color, and the presence of impurities. Star rubies or sapphires, for example, are cut with cabochons to emphasize the unusualness of the stone, transparent varieties are cut with ovals, circles or drops, like diamonds.
| Mohs hardness | Mineral Examples |
| 1 | Talc, graphite |
| 2 | Ulexite, Muscovite, Amber |
| 3 | Biotite, chrysocolla, jet |
| 4 | Rhodochrositis, fluorite, malachite |
| 5 | Turquoise, rhodonite, lazuirite, obsidian |
| 6 | Benitoite, Larimar, Moonstone, Opal, Hematite, Amazonite, Labrador |
| 7 | Amethyst, pomegranate, varieties of tourmaline indigolite, verdelite, rubellite, sherl), morion, agate, aventurine, citrine |
| eight | Green corundum (emerald), heliodor, topaz, painite, taffeite |
| nine | Red corundum (ruby), blue corundum (sapphire), leucosapphire |
| ten | Diamond |
Jewelry stones
All minerals whose hardness on a scale of less than 7 are considered soft, those above 7 are hard. Solid minerals can be processed with diamonds, the variety of possible cuts, transparency and rarity make them ideal for use in jewelry.
The hardness of the diamond on the Mohs scale is 10. Diamonds are faceted so that during processing the loss in stone mass is minimal. A processed diamond is called a diamond. Due to its high hardness and resistance to high temperatures, diamonds are almost 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 less cracks in it, the higher the price.
Semiprecious stones
Slightly lower than diamond and corundum, topazes and garnets are valued. Their hardness on the Mohs scale is 7-8 points. These stones lend themselves well to diamond processing. Price depends on color. The more saturated the color of topaz or pomegranate, the more expensive the product with it will cost. Extremely rare yellow topazes and purple garnets (majorites) are most highly valued. The last stone is so rare that its price can be higher than a pure diamond.
Colored tourmalines: pink (rubellite), blue (indigolite), green (verdelite), watermelon tourmaline are also referred to as semiprecious stones. High-quality transparent tourmalines are very rare in nature, which is why they are sometimes much more expensive than pyrope and blue topaz, and collectors do not tire of hunting for watermelon (pink-green) stones. The hardness of stones on the Mohs scale is quite high and amounts to 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 (sherl) belongs to ornamental stones. Sherl is a hard, but at the same time brittle stone, which can easily collapse during processing. It is for this reason that black tourmalines are most often sold untreated. Sherl is considered the strongest protective talisman.
Industrial application
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 devices.
Practical application of the scale
Although the Mohs hardness scale provides only a qualitative, not a quantitative, assessment, it is widely used in geology. Using the Mohs scale, geologists and mineralogists can approximately identify an unknown rock depending on its susceptibility to scratching with a knife or glass. Almost all reference sources indicate the hardness of minerals precisely on the Mohs scale, and not their absolute hardness.
In jewelry, the Mohs scale is also widely used. The hardness of the stone depends on the method of processing, possible polishing options and the necessary tools 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 them is the Rockwell scale. The Rockwell method is simple - it is based on measuring the depth of penetration of the identifier deep into the material under study. A diamond tip is usually used as an identifier. It is worth noting that minerals are rarely tested using the Rockwell method, it is usually used for metals and alloys.
Shore hardness scales are constructed in a similar way. The Shore method allows one to determine the hardness of both metals and more elastic materials (rubber, plastic).