Moh's Hardness Scale
There are two methods for measuring the hardness of materials: scratch hardness and static load indentation hardness. Scratch hardness, also known as Mohs hardness, is a relative hardness and is quite rough.
It uses ten natural minerals as standards. The hardness order does not represent the absolute size of the hardness of a given mineral, but it indicates that a mineral of a higher order of hardness can scratch a mineral of a lower order of hardness. The hardness of other minerals is determined by comparison with these standard minerals.
The Mohs unit of hardness is kilogram-force per square centimeter (kgf/cm²), denoted as (Pa). It is a standard for expressing the hardness of a mineral, first proposed in 1824 by the German mineralogist Frederich Mohs. Hardness is represented by the depth of the scratch made on the surface of the mineral tested by the pyramid-shaped diamond needle scratch method.
The hardness scale is as follows: talc 1 (softest), gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase (also known as feldspar or periclase) 6, quartz 7, topaz 8, corundum 9, diamond 10 ( harder) . Mohs hardness is also used to express the hardness of other solid materials.
| Level | Minerals | Equivalent to |
| 1 | Baby powder | None |
| two | Plaster | Fingernail |
| 3 | Calcite | copper coin |
| 4 | Fluorite | iron nail |
| 5 | Apatite | Glass |
| 6 | Orthoclase | Switchblade |
| 7 | Quartz | File |
| 8 | Topaz | Sandpaper |
| 9 | Corundum | None |
| 10 | Diamond | None |
For a more specific method: one would scratch the mineral to be tested against the standard hardness on the Mohs hardness scale to determine the hardness of the mineral being tested.
For example, if a mineral can scratch calcite and be scratched by fluorite, then the hardness of that mineral is between 3 and 4. Alternatively, one can use a fingernail (hardness 2-2.5), a coin (hardness 3, 5) or a small knife (hardness 5.5) to scratch the mineral to broadly determine its hardness.
| Representative Mineral Names | Common uses | Hardness Scale |
| Talc, Graphite | Talc is the softest known mineral, commonly used in the form of talcum powder. | 1 |
| Skin, Natural Arsenic | 1.5 | |
| Plaster | Industrial Materials | two |
| Ice Cube | 2~3 | |
| Nails, Amber, Ivory | 2.5 | |
| Gold, silver, aluminum | 2.5~3 | |
| Calcite, Copper, Pearls | Calcite can be used as a sculpture material and industrial raw material. | 3 |
| Shells, coins | 3.5 | |
| Fluorite (also known as fluorite) | Sculpture, Metallurgy, Building Materials | 4 |
| Platinum | Rare Metals | 4~4.5 |
| Iron | 4~5 | |
| Phosphorite | Phosphorus is an important component of biological cells; It is used as a raw material in the production of feed, fertilizers and chemicals. | 5 |
| Glass, Stainless Steel | 5.5 | |
| Orthoclase, Tanzanite, Pure Titanium | 6 | |
| Teeth (outer layer of the crown) | The main component is hydroxyapatite. | 6~7 |
| Soft Jade – Hetian Jade from Xinjiang | 6~6.5 | |
| Pyrite | It is used as a raw material for the production of sulfuric acid; gold refining; and can also be used for medicinal purposes. | 6.5 |
| Hard Jade – Burmese Jadeite and Jade | 6.5~7 | |
| Quartz Glass, Amethyst | 7 | |
| Electric Stone, Zircon | 7.5 | |
| Quartz | According to the ancient hardness scale, quartz is classified as 7. | 8 |
| Peridot | 8.5 | |
| Topaz, chrome, tungsten steel | On the ancient hardness scale, topaz is rated an 8. | 9 |
| Moissanite | Synthetic gemstones are 2.5 times brighter than diamonds and cost 1/10 the price. | 9.5 |
| Grenade | 10 | |
| Melted Zirconia | 11 | |
| Corundum | Corundum is rated 9 on the old hardness scale. Natural gemstones such as rubies and sapphires are now considered types of corundum, as are the hardness of synthetic sapphire crystals. | 12 |
| Silicon Carbide | 13 | |
| Boron Carbide | 14 | |
| Diamond | Diamonds are rated 10 on the ancient hardness scale, making them the hardest natural gemstone on the planet. | 15 |
What is Mohs hardness?
Mohs Hardness is a standard that indicates the hardness of minerals, first proposed in 1824 by the German mineralogist Friedrich Mohs. This pattern is established by using a pyramid-shaped diamond drill bit to scratch the surface of a mineral, with the depth of the scratch indicating the hardness.
The hardness of a mineral refers to its ability to resist certain external mechanical forces, such as scratching, indentation or grinding. In mineralogy, the hardness often referred to is Mohs hardness, which is scratch hardness compared to the Mohs hardness scale.
The Mohs hardness scale is based on ten minerals of different hardness, divided into ten levels from low to high: 1. Talc; 2. Plaster; 3. Calcite; 4. Fluorite; 5. Apatite; 6. Orthoclase; 7. Quartz; 8. Topaz; 9. Corundum; 10. Diamond.
In use, standard minerals are scratched against minerals of unknown hardness. If the mineral can be scratched by apatite but not fluorite, its hardness will be determined between 4 and 5.
This method was established and named by the German professor of mineralogy Friedrich Mohs (1773-1839). However, accurately measuring mineral hardness still requires a microhardness tester or hardness tester. Mineral hardness is also one of the physical properties of minerals. Minerals with high hardness have been widely used in industrial technology.
Diamonds, corundum and other minerals are not only used in industry, but also become precious stones. As precious stones, they generally have high hardness.
For example, the hardness of opal is 5.5-6.5, of quartz is 6.5-7, of sphalerite is 7.5-8. Tsavorite is 8.5, and the hardness of sapphires and rubies is 9, second only to diamonds. People choose high-hardness minerals as gemstones, probably because they are wear-resistant, symbolizing their timeless value!
According to needs, people have also developed a gemstone hardness scale to identify the mineral hardness of gemstones, from the softest to the hardest minerals: talc, gypsum, calcite, fluorite, apatite, zircon, corundum, silicon carbide , boron carbide, diamond, etc.
When there is no standard hardness mineral, the simplest way to measure hardness is with your fingernail or a small knife. The hardness of a fingernail is 2.5, of a copper coin is 3, and of glass and a small knife are both 5. Those above 6 are almost all gemstone-like minerals.
