What is the Mohs scale?

The Mohs scale and the hardness of stones

The Mohs scale measures the hardness of precious and semi-precious stones. It is, therefore, a hardness scale. But how exactly does it work? In this article, we'll explain everything so you can determine which stone is the hardest. You'll even be able to measure the hardness of diamonds!

What do you need to know about the Mohs scale?

Hardness is a property of materials such as gemstones. Most encyclopedias define it as a material's resistance to permanent penetration under static or dynamic load, after several tests. Generally, good hardness means a gemstone is resistant to scratches, wear, and abrasion—a very important characteristic in jewelry making. There is a close correlation between a material's hardness and its resistance.

The Mosh scale has remained a widely used technique for measuring the hardness of stones worldwide for over 200 years, primarily because it is practical, economical, and above all, easy to understand. Early hardness tests were based on the behavior of minerals according to their ability to scratch a softer mineral.

To do this, a scale called the Mohs scale was defined, with values ranging from 1 (very soft) to 10 (very hard), where 1 represented talc and 10 diamond. Some geologists use common objects for Mohs hardness testing 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.

Is there a material harder than diamond or softer than talc?

Diamond is not the hardest material. However, materials harder than diamond are extremely rare. Boron nitride, for example, can be harder than diamond. As for talc, it is unlikely you will find a softer mineral. Furthermore, some metals can be softer, such as rubidium.

How to identify a stone using the Mohs scale?

The Mohs hardness test determines the relative hardness of any mineral, using a scale. This allows you to determine which minerals can be scratched with a standard mineral on the scale; this is how the type of stone is distinguished. For example, according to the Mohs scale, calcite is harder than plaster. In other words, calcite can scratch plaster. Similarly, quartz is harder than calcite. Therefore, it can scratch plaster.

And finally, diamond can scratch all the minerals beneath it because it is the hardest mineral. Standard materials that can be used to determine a mineral's hardness are:

the nail (approximate hardness of 2)
the copper piece (hardness of 3)
a piece of glass (hardness of 5.5)
a steel nail (hardness of 6.5 to 7)

Mohs scale chart

Hardness	Examples
2	Nail
3	Copper piece
5,5	Piece of glass
6.5 to 7	Steel nail

Thanks to this system, you can measure the hardness of the stones in your jewelry and therefore identify them more easily. If you are looking for luxury watches set with genuine precious stones, be sure to check out the Chanel J12 Diamond.

What is the hardness of stones and how is it measured?

The hardness of a stone is its resistance to being scratched by another stone. To measure this hardness, you must place a sharp point of a stone of known hardness on the surface of another mineral of unknown hardness and try to scratch it. Consider the following information when measuring the hardness of a stone:

If stone A scratches stone B, then stone A is harder than stone B
If stone A does not scratch stone B, then stone B is harder than stone A
If the two stones have the same hardness, they will be ineffective at scratching each other, or they will only produce very small scratches on the materials or metals.

Mohs test procedure

First, find a smooth or clean face or surface of the mineral (whose hardness is unknown). Hold the mineral of unknown hardness in one hand, securing it to a surface (such as a table). Hold a stone of known hardness in your other hand. Then, try to scratch the stone of unknown hardness with the stone of known hardness.

Next, examine the surface of the mineral and answer the question: "Did the test produce any scratches?" Note whether a groove or a depression has formed on the surface. Repeat the test to confirm your results.

Uses and applications

The Mohs hardness test is used to measure the relative hardness of minerals, metals, stones, precious stones, and semi-precious stones. This scale is important for geologists as they use it to identify stones based on their hardness. Jewelers also use this scale to determine the hardness of gemstones. The technique allows for the identification of precious stones such as diamonds. For your jewelry, if you prefer to have this test performed by experienced jewelers, you can visit our jewelry workshop in Mulhouse.

FAQ

How to use the Mohs scale?

On the Mohs scale, stones are compared to each other by ranking them from 1 to 10 according to their ability to scratch each other. This is how their hardness is measured.