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
Q1: What are the Disadvantages of the Mohs Test?
Ans: Certainly, in the determination procedure, it is necessary to ensure that a scratch is made in reality or it is just a “chalk” mark that will rub off.
Additionally, when the species being tested is fine-grained, friable, or pulverulent, we say that the test may just extricate grains without testing singular mineral surfaces.
Subsequently, certain surfaces or total structures may thwart or forestall a genuine hardness determination.
Even so, the Mohs test, a well-known test for the identification of minerals in the field fails.
The failure is its inaccurate measure in the hardness of industrial materials such as steel or ceramics.
In contrast, for these materials, a more precise measure is to be discovered in the Vickers hardness or Knoop hardness.
Q2: Is Mohs Scale Linear?
Ans: No. The Mohs scale is not linear.
As a matter of fact, in this scale, each increment of one in the scale does not indicate a proportional increase in hardness in the first place.
For instance, the progression from calcite to fluorite is from 3 to 4 on the Mohs scale. This increase reflects a 25 % increase in hardness of approximately.
However, the progression from corundum to diamond, on the other hand, is from 9 to 10 on the Mohs scale.
In all honesty, the increment from calcite to fluorite and then again from corundum to diamond reflects a hardness increase of more than 300 percent, which is an inconsistent rise.
Q3: List the Tests for Mineral Hardness.
Ans: Besides Mohs Test, we have the following tests for measuring hardness:
Shore Hardness Test: The two following categories are:
Shore A - This test deals with soft polymers and elastomers, e.g. rubber.
Shore D - This test deals with hard polymers, like thermoplastics.
Brinell Hardness Test
This test is a standardized test applied especially to metals. It is defined by the standard ASTM E10. Also, it uses force ranging between 500 kgf and 3000 kgf.
Rockwell Hardness Test
A well-known test for measuring hardness in todays’ world. It is defined in the terms of ASTM E18.
Vickers Hardness Test
An advanced version of the Mohs Scale hardness test, also known as microhardness. It can measure the hardness at micro levels, defined in ASTM E384.
Knoop Hardness Test
Analogous to the Vickers test, the Knoop hardness test measures at a microscopic level and uses a force load of 1 kgf or less.
