Buzz
The Mohs hardness scale is a tool used to determine the relative hardness of minerals, gemstones, and even everyday items. It ranks 10 minerals based on their ability to scratch or be scratched. This test is commonly used by geologists and gemologists, and the minerals in the test are always the same. National Park ServiceMain Points
- Geologists and gemologists utilize the Mohs hardness scale to assess the "scratch resistance" of minerals and gemstones, ranking them according to their ability to either scratch or be scratched by other substances.
- To carry out the Mohs hardness test, simply drag one specimen across another and check if it leaves a scratch. This can easily be done with household items without any special equipment.
- Diamond is the hardest mineral on the Mohs scale and can scratch all other minerals, while all other minerals are capable of scratching talc, the softest mineral.
Diamonds are eternal. While we can't speak to their symbolic permanence, in geological terms, diamonds have certainly withstood the ages; they are among the hardest gemstones on the planet.
The incredible strength of diamonds was categorized using a scale established in the early 19th century: the Mohs hardness scale. With a ranking of No. 10, diamonds are among the hardest substances known to humankind.
History of the Mohs Scale
Created by German mineralogist Friedrich Mohs in 1812, the scale categorizes minerals by their hardness. Mohs drew inspiration from the methods used by botanists to classify plants and from Pliny the Elder, who, over a millennium ago, compared the hardness of diamond and quartz.
Building on Pliny's work, Mohs outlined 10 hardness values that allowed for the comparison of minerals based on their ability to scratch one another. The scale ranged from very soft (talc) to extremely hard (diamond). Prior to Mohs' scale, minerals were classified by their chemical composition, which lacked uniformity, as noted by the European Geosciences Union blog.
The Mohs Hardness Test
The Mohs hardness scale serves as the industry standard for geologists and gemologists when classifying minerals and gemstones. They use the Mohs hardness test to assess a material's ability to be scratched. For example, since diamond can scratch quartz, diamond is considered harder than quartz.
This test is quite simple to perform, whether in a lab or on your kitchen table. Begin with two specimens with smooth, unmarked surfaces. Secure one in place on the table. Take the sharp edge of the second specimen and drag it firmly across the surface of the first. If a scratch forms, the second specimen is harder. If no scratch appears, the second specimen is either softer or of equal hardness. In that case, switch the roles and test whether the first specimen can scratch the second.
Be sure that the mark you observe is indeed a scratch—a groove in the material—not just a residue left by a softer material used in the test.
Where Stuff Ranks
On the Mohs scale, which ranks 10 minerals, diamond tops the list at No. 10 as the hardest, while talc sits at No. 1 as the softest. Many substances can be placed on this scale, such as ruby, which ranks at 9, tanzanite, which falls between 6 and 7, and soapstone countertops that measure around a 3. Even more than just minerals and rocks can be assessed. For example, a fingernail, rated at 2.5, cannot scratch a diamond, nor can a steel nail, which rates at 6.5.
While diamond is the hardest material on the Mohs scale, there are six materials now known to be harder, including substances like wurtzite boron nitride and a pure lonsdaleite meteorite. However, the remaining four of these harder materials are not naturally occurring.
