The mineral hardness scale or Mohs mineralogical scale is compiled from reference samples according to the degree of relative hardness from 1 to 10. A qualitative ordinal indicator of the strength resistance of minerals included in this scale is determined by scratching. The mechanical ability of harder materials to scratch softer rocks determines the relative hardness of a particular type of mineral.
The 10 Mohs mineral elements are presented as reference samples and arranged in ascending order, allowing you to visually determine which mineral is harder. For example, talc occupies the first position in the table and is considered the softest among others presented on the scale. On the other side is a diamond, which, according to the “mineral strength” criterion, occupies the very top, that is, the 10th position on the Mohs scale and has no analogues in nature in terms of this indicator.
Creation and purpose of the Mohs scale in modern practice
This system was created at the beginning of the 19th century by the German geologist, mineralogist and inventor of the time, Friedrich Mohs. Since then, many similar methods have been created in geology to determine the hardness index, including the Knoop, Brinell, Vickers and Rockwell methods.
Mohs scale minerals, determined by hardness, are distributed according to relative integer comparisons. This comparison is based on the scratch resistance of the sample. There are popular methods that use indentation resistance as a comparative characteristic.
These research methods use an indenter as a testing tool, pressing it into the piece of mineral rock being tested. In this case, thorough measurements of the force indicator of pressure are made. The obtained indicators of the size and depth of the excavation, taking into account the pressure force, make it possible to calculate hardness indicators.
But in such measurement methods, a variety of technical devices and calculation methods are used for testing. Therefore, direct comparisons of the obtained indicators for different minerals under different conditions are not directly comparable with each other.
Thus, the Mohs scale has become more widespread - the technique itself is simpler and cheaper to implement and is more accessible to understanding. On the other hand, this type of measurement is not capable of providing the highest degree of accuracy. Nevertheless, it is relevant among modern geologists working in the field.
It is often used for the initial determination of the type of mineral rocks when examining obtained samples in situ, when more complex tests are difficult or impossible. That is why the results of measuring hardness on the Mohs scale are usually called relative.
Stones for sharpening knives: the best by manufacturer
The best manufacturers of stones for sharpening knives are considered to be Russia, Japan, China and the USA; Soviet-made tools can still be found on sale, and many professionals prefer them.
Russian made: Petrograd, Grinderman, Gritalon
Sharpening stones, which are produced in Russia, are distinguished by the correct price-quality ratio.
Of the most popular, it is worth highlighting:
| Name | Description | Photo |
| "Petrograd" | This brand produces silicon carbide stones that are distinguished by a variety of surface hardness. It is important that the degree of graining exactly corresponds to Japanese standards - they are recognized throughout the world as the best. | |
| "Grinderman" | The production is located in St. Petersburg, the company not only produces various sharpening tools, but also provides full service. | |
| "Gritalon" | They produce synthetic abrasive tools that can be used both for sharpening machines and for manual work. The material used in production is silicon carbide. |
Japanese: Suehiro, YOSHIKIN, Yaxell, Samura
Sharpening stones made in Japan are usually used for manual work and with water; the most famous brands of such tools are:
- Suehiro;
- Yoshikin;
- Yaxell;
- Samura
The difference between such stones is that when sharpening cutting surfaces, new layers of abrasive are constantly “opened”, and particles of the previous ones are mixed with water and have the best possible effect on the blade.
Sharpening stone Samura Sharpening stone Yaxell Sharpening stone Global MinoSharp from the manufacturer Yoshikin Sharpening water stone Suehiro
The Japanese produce sharpening stones with different degrees of grain, so when using a tool with fine grains at the last stage, it makes it possible to bring the cutting surface to perfect condition without the additional use of pastes, felt and dressing slings.
Japanese water stones are distinguished by the highest productivity, which can only be compared with diamond tools. But the latter increases the risk of excessive thinning of the blade at the final stage of finishing the cutting surface.
Japanese whetstone grit standards are recognized by international organizations and are used for designation by most manufacturers.
Soviet
Soviet sharpening stones are bars of absolutely regular shape, onto which a coating of abrasive material (base – silicon) was applied. You can still find Soviet sharpening stones and whetstones on sale at flea markets - they are considered high quality and “eternal.”
On the territory of the USSR, they used their own, individual markings, which are radically different from modern ones.
What was indicated on each product:
- dimensions;
- accuracy class;
- manufacturer (each had its own mark);
- dimensions;
- hardness level;
- structure characteristics;
- product type;
- material used in manufacturing;
- grain level.
Microcorundum block for straightening USSR razors, 1970
Chinese: Ganzo
Chinese sharpening tools include silicon carbide and aluminum oxide stones, which are characterized by fairly high quality, long service life and low cost. The most famous manufacturer is Ganzo. Such tools are especially good for sharpening ordinary kitchen knives - their grit level does not exceed 1000 grit, which allows you to bring the blade to the desired sharpness with one whetstone.
Recently, sharpening stones from China made of vacuum ceramics and boron carbide have appeared on the market. They have an almost eternal service life; even with prolonged sharpening of the tool, they do not wear out.
Chinese sharpening tool Ganzo
Arkansas: Dan's, Smith's, Lansky
Three companies stand out from the manufacturers:
- Dan's;
- Smith's;
- Lansky
Arkansas is a state in America where abrasive material is mined and grindstones are produced. Mineral reserves in this part of the country are already greatly depleted, so the cost of the tool is very high even by the standards of the Americans themselves. However, Arkansas stones have always been popular and are now considered the best quality on the market.
Lansky whetstone Smith's whetstone Dan's whetstone
How to determine the hardness of minerals using the Mohs scale?
It is often necessary to determine the type of mineral in the field, that is, in the absence of special laboratory conditions and appropriate instruments. For these purposes, a geologist just needs to use the Mohs scale and a few simple improvised means that can scratch.
For example, using a pocket knife, you can determine whether a sample is one of the less or harder mineral rocks, the Mohs value of which exceeds 5-6. Here is a table of some available items and their degree of hardness, which can help in determining the relative hardness, and, accordingly, the type of mineral:
Sharpening stones for machine tools
Sharpening stones for machine tools vary in shape and composition. They can be used for sharpening not only cutting tools, but also any other metal products. Most often you can find a stone made of silicon carbide, but the most durable is considered to be CBN - an abrasive material based on boron nitride, which makes the tool as durable as possible.
All sharpening stone attachments for machines are divided into two types: black – the most resistant/strong and green. The first is used for rough sharpening of the cutting surface, while green is used to bring it to the desired state.
Sharpening machine 150 mm Titan BNS25-150
Stones for knife
Ceramic and diamond stones are used for knife blades in the kitchen. They are characterized by fine grain and therefore cannot sharpen the cutting surface efficiently - usually such kitchen devices are used for quickly straightening the blade.
The service life of such blades is short, the abrasive coating on them is thin. Some manufacturers produce a device with three stones - coarse, medium and fine, which makes it possible to increase the level of sharpening of kitchen knives.
How to choose a sharpening stone for tools
The selection of a whetstone should be made taking into account the following parameters:
- Abrasive grain size . It can be small, medium and large. The latter is necessary to eliminate chips on the surface of the cutting tool, because only coarse grain size can remove layers of damaged metal.
- Material of manufacture . In terms of characteristics and service life, synthetic sharpening stones are many times superior to natural ones, but this ratio is appropriate to take into account only when choosing a device from the middle price category. If you are planning to purchase a high-quality sharpening stone, then you should pay attention to Japanese manufacturers.
- Dimensions . If a stone is purchased for sharpening kitchen knives, then the shape and size practically do not matter. But if you constantly use a sharpening device on hikes, at work you should choose small sizes, even pocket-sized options.
What grit to choose for sharpening a knife
The grain size for sharpening a knife should be selected depending on the goals pursued; experts say that you need to have at least 3 stones in your arsenal:
- 120 grit – for rough metal processing;
- 1000 grit – to level the surface;
- 2000 grit – for straightening the blade.
But practitioners believe that knives can be sharpened with a stone with a grain size of 1500 grit. Such kitchen tools come straight from the store sharpened and only need to be slightly adjusted during use.
Stone for dressing water stones
When using water stones, irregularities form on their surface, which impairs the quality of sharpening knives and other cutting tools; you can correct them:
- sandpaper;
- silicon carbide powder;
- sand;
- diamond block.
But it is easier and faster to sharpen the sharpening tool with special stones - synthetic water stones with diagonal cuts along the surface of the same depth. They can be hand-held or tabletop. In the first case, straightening is carried out with a stone with cuts, in the second, the damaged whetstone is ground/straightened on a fixed one.
The most popular stones for dressing water stones:
| Name | Description | Photo |
| Table stone from the Large series NANIWA Flattening Stone for Sharpening Stones (Truing Stone) | It has the same grain size (24 grit) and is made of silicon carbide. | |
| Table stones from the JUUMA Flattening Stones series | Made from aluminum oxide, they are a series of four stones of different grain sizes. It is noteworthy that they are able to rule even each other. | |
| Suehiro Hand Stones | They have a medium grain size (200 grit), are intended for straightening synthetic water stones, correcting both subtle unevenness and deep “pits” and grooves. |
Which sharpening stone to choose for kitchen knives
For kitchen knives, it is better to choose a water sharpening stone - they “work” faster and allow you to straighten the cutting surface without changing tools until you get the desired result. But you need to remember that some knife materials can rust when in contact with water, which will hopelessly ruin your kitchen tool. In this case, it is better to use oil sharpening stones - sharpening takes a long time, but it is always of high quality, and the blade of the knives does not rust.
As for the grit level of the whetstone, 1500 grit is sufficient for kitchen knives, because 240 grit is too coarse an abrasive surface that greatly thins the knife blade.
