Mohs Hardness Scale Meaning
The discoverer of the Mohs Hardness Scale was a German geologist and mineralogist named Friedrich Mohs, which he did in the year 1812. This scale was so named after him.
Mohs Scale gives a rough estimate of the resistance/obstruction of a smooth surface to scratching/abrasion. Here, the calculation is done by using the Mohs Hardness Scale.
We study the concept of the Mohs Hardness Scale under the domain of Mineralogy. Mohs hardness of a mineral can be determined by knowing if its surface is scratched by a known or an undefined hardness.
This page discusses the Mohs hardness scale along with the scale for mineral hardness
In detail.
What is Mohs Scale?
Mohs Scale of Mineral Hardness helps us determine the type of hardness where the attribute “hardness” is a physical property in Mineralogy.
To assign a numerical value to this attribute, minerals are ranked according to the Mohs scale, Mohs scale is made out of 10 minerals that are doled out at arbitrary hardness values.
Now, let’s have a look at the name of the 10 minerals with their ranking on the Mohs scale of mineral hardness:
Mohs Scale of Mineral Hardness
The Mohs scale of mineral hardness is the ability of one natural sample of mineral to scratch another mineral visibly (in reality).
The samples of matter used by Mohs are 10 different minerals, it may include other materials to determine the approximate hardness of the mineral.
So, do you know what minerals are? If not, let’s understand:
Well! minerals are chemically natural pure solids. At the same time, rocks are made up of one or more minerals.
Rocks are the hardest known naturally occurring substances according to the Mohs scale. As a result, diamonds are at the top of the Mohs scale.
We can measure the hardness of a material against the Mohs scale by finding the hardest material that can scratch the given material or the softest material that can scratch the given material, and vice-versa.
For instance, if we scratch a material by apatite, not by fluorite, its hardness on the Mohs scale lies between 4 and 5.
So, Why Do We Study Scratching?
In all honesty, "Scratching" material for the purposes of the Mohs scale means creating non-elastic ocular (visible to the naked eye) dislocations.
Regularly, we find that minerals at a lower level on the Mohs scale make infinitesimal, inelastic disengagements on materials and they have a higher Mohs number. Additionally, they have an inocular (not noticeable to the unaided eye) impression.
While these microscopic dislocations are permanent (not just a powder that rubs off). However, sometimes these dislocations are detrimental to the structural integrity material’s hardness.
Also, they are not accounted as "scratches" for determining a Mohs scale numerical value.
What is the Mohs Scale?
The Mohs scale is an innate ordinal scale. The table below ranks the minerals on the basis of their hardness level (Hardness Scale) in descending order on the scale for Mineral hardness:
Point to Note: This table also contains other materials that round off the hardness values of some of the minerals.
Hardness Values of Some of the Minerals
Images of Minerals
Scale for Mineral Hardness
The above table indicates a raming in a scale. So, when a mineral is scratched by orthoclase, its value on the hardness scale lies between 5 and 6.
Also, we note that corundum (9th rank) is twice as hard as topaz (8th rank); however, diamond (at 10th rank) is four times as hard as corundum.
Mohs Hardness Scale Uses
In spite of its lack of precision, the Mohs scale is suitable for field geologists, who employ the scale to recognize minerals (approximately) using scratch kits. We commonly find the Mohs scale hardness of minerals in reference sheets.
Mohs hardness is a useful concept in milling. Here, it helps us determine the kind of mineral mill produces such that it will best reduce a given product whose hardness is known.
Likewise, the electronic makers utilize this scale for testing the strength of flat panel display components, like covering glass for LCDs and exemplification for OLEDs.
Additionally, the Mohs scale is being used to ascertain the hardness of smartphone screens.
Furthermore, you often find the Gorilla Glass glass for mobile phones on shopping websites, like Amazon or Flipkart.
The Specialty of a Gorilla Glass:
The modern smartphone displays use Gorilla Glass because it is so protective that scratches at level 6 with deeper grooves at level 7 on the Mohs hardness scale.
Do You Know?
Theophrastus in his composition On Stones, c. 300 BC alongside Pliny the Elder in his Naturalis Historia, c. AD 77 referenced the technique for looking at hardness by seeing which minerals can scratch others is of the extraordinary relic.
The Mohs scale is very helpful for the recognizable proof of minerals in the field yet is certifiably not an exact indicator of how well materials suffer in a mechanical setting - sturdiness.
FAQs on Mohs Hardness Scale
1. What is the Mohs Hardness Scale and what does it measure?
The Mohs Hardness Scale is a qualitative ordinal scale used in geography and geology to measure the relative scratch resistance of various minerals. Developed by German mineralogist Friedrich Mohs in 1812, it determines which minerals can visibly scratch others. A mineral is assigned a number from 1 to 10 based on its ability to scratch, or be scratched by, one of the ten standard minerals on the scale.
2. What are the 10 standard reference minerals on the Mohs Hardness Scale?
The ten standard minerals that define the Mohs Hardness Scale, ranked from softest to hardest, are:
1 - Talc
2 - Gypsum
3 - Calcite
4 - Fluorite
5 - Apatite
6 - Orthoclase Feldspar
7 - Quartz
8 - Topaz
9 - Corundum
10 - Diamond
3. How can you use everyday objects to estimate a mineral's hardness on the Mohs scale?
You can estimate a mineral's hardness in the field by using common objects with known hardness values. This is a practical application of the Mohs test. For example:
A fingernail has a hardness of about 2.5. It can scratch Talc and Gypsum.
A copper penny has a hardness of about 3.5. It can scratch Calcite but not Fluorite.
A steel nail or knife blade has a hardness of about 5.5. It can scratch Apatite but not Orthoclase Feldspar.
A piece of glass also has a hardness of around 5.5. If a mineral can scratch glass, its hardness is greater than 5.5.
4. Why is the Mohs scale considered an ordinal, not a linear, scale?
The Mohs scale is an ordinal scale because it only ranks minerals in order of their relative hardness; it does not represent a proportional or absolute increase in hardness. For example, the difference in absolute hardness between Corundum (9) and Diamond (10) is more than three times the difference between Corundum and all the other minerals from 1 to 8 combined. This non-linear relationship means an increase from 4 to 5 is not the same amount of hardness increase as from 9 to 10.
5. What are the primary limitations of using the Mohs hardness test for mineral identification?
While useful for quick field identification, the Mohs test has several key limitations:
It is not precise: The scale is relative and qualitative, not providing an absolute hardness value required for scientific or industrial purposes.
Can be misleading: The test may be inaccurate on minerals that are granular, impure, or have weathered surfaces, as it might just break grains apart rather than creating a true scratch.
Test is destructive: The scratch test can permanently damage or devalue a mineral specimen, which is a concern for rare or valuable samples.
Limited range: Many minerals fall between the standard numbers, requiring estimation (e.g., 6.5).
6. Why is understanding a mineral's hardness important in real-world applications like gemology?
Understanding a mineral's hardness is crucial for its practical use. In gemology, hardness directly relates to a gemstone's durability and suitability for jewellery. For instance, a diamond (hardness 10) is ideal for an engagement ring because it resists scratches from everyday exposure. A softer gem like Fluorite (hardness 4) would scratch easily and is therefore not recommended for daily wear. Hardness also helps distinguish real gems from imitations; for example, real Quartz (7) will scratch glass (5.5), while many glass imitations will not.
7. How does the Mohs scale compare to more precise hardness tests like the Vickers scale?
The Mohs scale and the Vickers scale measure hardness differently and serve distinct purposes. The Mohs scale is a simple, field-based relative scratch test useful for geologists to quickly identify minerals. In contrast, the Vickers hardness test is a quantitative, lab-based microhardness test. It uses a diamond indenter with a specific force to create a mark on the material. The size of this indentation is then measured to calculate an absolute hardness value, making it essential for engineering, metallurgy, and material science where precise, standardized data is critical.
