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What is the Mohs scale
What is the Mohs scale, the main differences from other methods for measuring the hardness of various materials (other methods are also briefly described in the article).
The Mohs scale (mineralogical scale of hardness) is a qualitative ordinal scale (specifically applied, not theoretical) is an ordinal scale that characterizes the resistance of different materials to scratching. That is, we can say in a simple way - the Mohs scale shows which material can scratch another material. In this scale, there are various definite and indefinite (generalized) various materials, which include single-component (metals, oxides) and multi-component (minerals, wood, alloys, precious stones).
Mohs Scale Based on the ability of a harder material to scratch a softer material (nothing more to say here).
The simple Mohs scale contains 10 reference minerals, which are ordered in order of increasing hardness from very soft (talc) to very hard (diamond).
Most of the minerals on the table (except diamond) are relatively common and easy or inexpensive to obtain.
- — Talc;
- — Gypsum;
- — Calcite;
- — Fluorite;
- — Apatite;
- —Orthoclase;
- — Quartz;
- — Topaz;
- — Corundum;
- — Diamond.
A simple version of the Mohs scale
The simplest version of the Mohs scale is below (actually applied hardness):
- 1 - Pencil (graphite);
- 2 - Table salt;
- 2-2.5 - Can be scratched with a fingernail;
- 2.5-3 - Gold, silver;
- 3 - Copper coin;
- 4-4.5 - Nail (mild steel alloy);
- 4-5 - Iron;
- 5 - Glass (the most common material for comparison and tests);
- 5-6,5 - Knife blade;
- 6,5 - Steel file (can already scratch glass);
- 7 - Easily scratches glass;
- 7+ - Hardened steel file (easily scratches glass);
- 8 - Sandpaper, the mineral scratches glass very easily;
- 9 - The mineral cuts glass (in fact, even a slight pressure is enough to leave strong marks on the glass);
- 10 - Used as a glass cutter.
Augmented Mohs Scale
Below is an extended table of the hardness of different substances on the Mohs scale:
|
Substance or mineral |
Mohs hardness |
|
Pyrophyllite, molybdenite |
1-2 |
|
Bauxite, coal |
1-3 |
|
Limonite |
1-5 |
|
Ice, sugar, gallium, strontium, indium, tin, barium, thallium, lead, graphite |
1.5 |
|
Gypsum, calcium |
1.5-2 |
|
Sulfur |
1.5-2.5 |
|
Sylvit, glauconite, cadmium, selenium |
2 |
|
Rock salt, cinnabar, chlorite, bismuth, amber |
2-2.5 |
|
Muscovite |
2-3 |
|
Silver, gold, galena, copper, biotite, mica |
2.5-3 |
|
Aluminum, limestone, calcite, boric acid, nitrophoska |
3 |
|
Aragonite, witherite, anhydrite |
3-3.5 |
|
Pearl, brass, arsenic |
3-4 |
|
Serpentine |
3-5 |
|
Sphalerite, rhodochrosite, malachite, dolomite, cuprite, chalcopyrite, azurite, barite |
3.5-4 |
|
Siderite, pyrrhotite, dolomite |
3.5-4.5 |
|
Fluorite, phosphor bronze |
4 |
|
Marble |
4-5 |
|
Tooth enamel, asbestos, apatite, manganese, zirconium, palladium, obsidian |
5 |
|
Titanite, monazite, glass |
5-5.5 |
|
Jade, uraninite, ilmenite, enstatite, porcelain stoneware (polished) |
5-6 |
|
Magnetite |
5-6.5 |
|
Nepheline, augite, arsenopyrite, actinolite, bustamite, cobaltite |
5.5-6 |
|
Rhodonite, diopside, opal, red ironstone |
5.5-6.5 |
|
Titanium, germanium, niobium, rhodium, uranium |
6 |
|
Rutile, pyrite, prehnite, plagioclase, orthoclase, amazonite, andesine, anorthoclase, benitoite, gelvin, iridium |
6-6.5 |
|
Silicon |
6.5 |
|
Jasper |
6.5-7 |
|
Agate, zoisite, epidote, cassiterite, pyrolusite |
6-7 |
|
Marcasite |
6-7.5 |
|
Granite, tanzanite, spodumene, olivine, jadeite, axinite, chrysoprase, jadeite |
6.5-7 |
|
Sillimanite, Garnet |
6.5-7.5 |
|
Quartz, quartz glass, stone pebbles, amethyst, aventurine, forsterite, osmium, silicone, rhenium, vanadium, chrome |
7 |
|
Tourmaline, cordierite, almandine, boracite, cordierite, danburite |
7-7.5 |
|
Zircon, andalusite, euclase, hambergite, sapphirine |
7.5 |
|
Emerald, hardened steel, tungsten, spinel, beryl, beryllium, aquamarine, red beryl, ganite, painite |
7.5-8 |
|
Topaz, Cubic Zirconia |
8 |
|
Chrysoberyl, alexandrite, holtite |
8.5 |
|
Porcelain stoneware (unpolished) |
8.5 |
|
Corundum, ruby, sapphire, alundum, chrome |
9 |
|
Moissanite, Boron |
9.5 |
|
Pobedit (tungsten carbide + carbon + cobalt) |
9.5-9.6 |
|
Carborundum (some grinding discs) |
9-10 |
|
Diamond, carbonado |
10 |
*Pobedit is highlighted on purpose, as most of the "good" wood and metal cutters are made from Pobedit.
The difference between the Mohs scale and other methods of measuring hardness
How does the Mohs scale (and technology) differ from other methods of measuring the hardness of various materials?
Despite the lack of accuracy of the Mohs scale, it is relevant for field geologists (and was originally intended for them), who use it for rough identification of minerals. Samples for research can be easily found in nature (with the exception of diamond). That is, this scale is aimed at determining the hardness of materials in a comparative way with low accuracy. But despite this, the Mohs scale has become widespread and has gained a foothold not only among researchers, but also in everyday use.
Brinell Scale
The Brinell hardness measurement method is one of the oldest methods, here the hardness is determined by the diameter of the imprint left by a metal ball pressed into the surface. This requires equipment that, with a measured force, will allow you to press a hardness tester (ball) into the material, and then, using a microscope or a magnifying glass, measure the diameter of the imprint left. Denoted HB, where H - Hardness (hardness, English), B - Brinell (Brinell, English)
Rockwell scale
The Rockwell hardness measurement method is the most common of the methods of the early 20th century, hardness is determined by the relative depth of indentation of a metal ball or diamond cone into the surface of the material being tested. It is designated HR, where H is Hardness (hardness, English), R is Rockwell (Rockwell, English), and the 3rd letter indicates the type of scale, for example. HRA, HRB, HRC, etc. The technique itself is very similar to the Brinell method.
Vickers Scale
The Vickers hardness measurement method has the widest scale in terms of coverage. Hardness is determined by the area of the imprint left by a tetrahedral diamond pyramid pressed into the surface. Denoted HV, where H - Hardness (hardness, English), V - Vickers (Vickers, English). The measurement technique is similar to the previous two.
Shor Scale
The Shore hardness method is rarely used; in this method, the hardness of the material is determined by the height of the rebound of the striker from the surface. It is designated HS, where H is Hardness (hardness, English), S is Shore (Shore, English), and the 3rd letter indicates the type of scale, for example. HSD
Lib Scale
The Lieb hardness measurement method is somewhat reminiscent of the Shor method, and (as they say, I don’t even think about it at all ...) is the most common method in the world. The hardness in this method is defined as the ratio of the speeds before and after the rebound of the striker from the surface. It is denoted by HL, where H is Hardness (hardness, English), L is Leeb (Lib, English), and the 3rd letter is the designation of the sensor type, for example. HLD, HLC, etc.
The hardness of the steel (or tools) is usually listed in the description or specifications.
In future articles, other scales and measurement methods will be described in detail.