The Mohs scale orders ten types of minerals based on their hardness, where the first mineral (talc) is the one with the lowest hardness and the last mineral (diamond) is the one with the highest hardness.
The Mohs scale has remained a widely used technique throughout the world for more than 200 years, mainly because it is easy to do, it is inexpensive, and above all, it is easy to understand.
Mohs scale
In total there are ten minerals ordered from lowest to highest hardness, you can click on the name of each mineral to learn more about its properties and characteristics.
| Mohs hardness scale (minerals) | Mohs hardness |
|---|---|
| Talcum powder | 1 |
| Gypsum | 2 |
| Calcite | 3 |
| Fluorite | 4 |
| Apatite | 5 |
| Orthoclase | 6 |
| Quartz | 7 |
| Topaz | 8 |
| Corundum | 9 |
| Diamond | 10 |
Hardness and Mohs scale of some common objects
Some geologists and people use common objects for Mohs hardness tests in the field.
A fingernail, a copper coin, a nail, a piece of glass, a blade, a steel file, and a piece of quartz are common objects suggested in some geology textbooks.
| Mohs hardness of some common objects | Hardness |
|---|---|
| Fingernail | 2 to 3 |
| Copper strip | 3 |
| iron nail | 4 to 5 |
| Glass cup | 4 to 7 |
| Knife’s blade | 5 to 6.5 |
| steel file | 5 to 6.5 |
| Steel nail | 5 to 7 |
| Quartz | 7 |
The table above lists the range of hardnesses we found in suggested common items for field hardness testing, without doing an exhaustive search.
Is there any material harder than diamond or softer than talc on the Mohs scale?
You may not know that diamond is not the hardest known substance, however materials that are harder than diamond are quite rare.
Some of the materials that can be harder than diamond are wurtzite boron nitride and losndaleite.
Regarding talc, it is unlikely that you will find a softer mineral.
However, some metals have been found to be softer.
Some materials softer than talc are: cesium, rubidium, lithium, sodium and potassium.
How to identify a mineral with the Mohs scale?
The test of the Mohs hardness determines the relative hardness of any mineral, taking into account the scale, it is established which mineral of the scale can be scratched with a standard mineral of the scale, it is thus that the type of mineral is distinguished.
For example, according to the scale, calcite is harder than gypsum and could scratch this mineral.
Also, quartz is harder than calcite, therefore quartz could easily scratch calcite.
And finally, the diamond can scratch all the minerals below it because it is the hardest mineral.
Standard materials that can be used to determine the hardness of the mineral are: a fingernail (approximate hardness of 2), a copper coin (hardness of 3), a piece of glass (hardness of 5.5), a steel nail ( hardness from 6.5 to 7)
What is mineral hardness and how is it measured?
The hardness of minerals corresponds to the resistance offered by the face or external surface of the mineral with unknown hardness, to being scratched by another mineral or material with known hardness.
The hardness of minerals is controlled by the weakest bonds in their internal structure.
The hardness test is known as the Mohs scale, and it is one of the tests most used by geologists to distinguish minerals.
“Hardness” is the resistance of a material to being scratched by another material of known hardness.
Hardness is measured by placing a sharp point of a known material on the unmarked surface of another mineral and trying to scratch the surface.
You must take into account the following considerations to estimate the hardness of the two samples:
- If Sample A can scratch Sample B, Sample A is harder than Sample B.
- If Sample A does not scratch Sample B, then Sample B is harder than Sample A.
- If the two samples are equal in hardness, then they will be relatively ineffective at scratching each other. Minor scratches may occur, or it may be difficult to determine if a scratch has occurred.
- If Sample B can be scratched by Sample B but Sample C cannot scratch it, then the hardness of Sample A is between the hardness of Sample B and Sample C.
Mohs test procedure
- First, you have to look for a face or surface of the mineral (of unknown hardness), which is smooth or clean.
- With one hand, you must hold the mineral that has unknown hardness, the mineral must be fixed, so it is recommended to use a support (a table).
- With the other hand you must hold a mineral or material that has standard hardness
- You should try to scratch the mineral of unknown hardness with the mineral of standard hardness.
- He then proceeds to examine the surface of the mineral and answers: Did the test produce any scratches? It must be noted that a groove or hole has formed on the surface.
- Run the test a second time to confirm your results.
Uses and applications
The Mohs hardness test is used almost exclusively to identify the relative hardness of various types of minerals.
This scale is very important for geology students and also for geological engineers as they use it to identify minerals in the field according to their hardness.
Subsequently, laboratory tests are carried out to determine the exact hardness of the mineral and the type of mineral.
In industry, other hardness tests are performed to determine a material’s suitability for a specific industrial process or end-use application, but the Mohs scale is an initial approximation of a material’s ideal hardness.