Understanding the Mohs Scale and the Durability of Gemstones

Whenever you talk about the hardness of minerals and gemstones, you might have heard people from the industry measure the hardness on the Mohs Scale. The rating on the Mohs scale is actually one of the most important tests for the quality of mineral specimens and this comes in handy when you are looking to purchase jewelry.

For example, if you buy a ring that contains Gypsum, you might want to rethink that since this stone has a hardness rating of 2 on the Mohs Scale, which is low and subsequently it may often get scratched due to the continuous movement and friction to other materials when working with our hands. Deciding to wear it as an earring would be more practical. We are going to take a look at exactly what is the Mohs scale and some other qualities of gemstones which allow us to properly determine the durability of them.  

What Is The Mohs Scale?

The Mohs Scale or the Mohs Hardness Scale was created in the early 1800s by a man called Friedrich Mohs. He was considered to be one of the most renowned mineralogists at the time. He created this measure in order to find out and determine the comparative resistance that a mineral has to scratching.

The Mohs Hardness scale was revolutionary for the mineral and gemstone industry because right after the creation, people were able to use this scale to classify the durability of gemstones. However, if you are looking for a truly durable gemstone that can withstand the test of time, there is more to determining just durability besides the hardness on the Mohs Scale.

This scale is essentially based on a resistance factor that a mineral has to scratching. It is considered to be the only characteristic that is used to measure and determine the rank of the gemstones on the scale.

According to the findings of Friedrich Mohs and the Mohs Scale that he created, a gemstone can only be scratched by another gemstone that ranks higher. For instance, you cannot expect Topaz to be able to scratch Quartz because Topaz has a reading of ‘8’ and Quartz has a reading of seven. That means Quartz is softer than the Topaz. Similarly, you can expect Corundum to be able to scratch Topaz because Corundum registers at ‘9’ on the Mohs Hardness Scale.

It’s important to keep in mind that the Mohs Scale is not necessarily a linear one. This means that even though diamonds register at a reading of 10, they are not 10 times as hard as Talc, which registers as ‘1’. The Mohs Scale is only a measure of resistance that a stone has to surface scratching.

While the Scale is considered to be one of the most important factors in determining the durability of a gemstone, it is only a single aspect of it. The overall durability of a gemstone can be different from the surface resistance that it has since surface resistance is only one factor when testing durability. For instance, an emerald has a Mohs Scale rating of 8 but it does not wear as well as a Topaz which also rates as 8. This is because there are additional characteristics within the emerald stone that make its overall durability different.  

Other Factors that Determine Gemstone Durability

Rose Quartz Healing Gemstone
Rose Quartz Healing Gemstone

If the Mohs Scale is not enough to determine the overall durability of a gemstone, what are the characteristics of gemstones that make them totally durable?

Ther additional properties and characteristics to determining the durability or how well they respond to the test of time are: cleavage, molecular bonds, stability, treatments and enhancements among other things.

Let’s take a look at some of the most important determining factors for the durability of a gemstone.

Cleavage

The gemstone cleavage is its ability to break cleanly along a certain distinct line. This depends on the crystalline structure that the different kind of gemstones have. Gemstones can have either a perfect cleavage, a completely non-existent one or anywhere in between the two extremes.

Diamonds have perfect gemstone cleavage. It means that a diamond can be split into two pieces by striking it at the perfect spot even with a softer mineral. The cleavage is particularly important when it comes to the shaping and polishing of stones. Lack of knowledge about the cleavage of a gemstone can ruin even the hardest gemstones on the Mohs Scale.

Stability

The stability is based on how well the mineral can endure different conditions in the environment; such as pressure, chemicals, and temperatures. Some gemstones like the unheated amethyst can lose their natural color upon exposure to heat. Opals are minerals that are particularly susceptible to changes in temperature. They can even crack if there is a sudden temperature change. which indicates that they are not one of the most stable minerals.

A set of molecules

“DSC_2324b.jpg”by i(saw) e(saw) is licensed under CC BY-NC 2.0

Molecular Bonds

The crystalline structure or the molecular bonds of a gemstone are another important factor in determining overall durability. There are stones that have a high rating on the Mohs Hardness Scale but their overall durability happens to be low because their molecular structure is not that strong. Jade happens to have a 7.0 rating on the Mohs Scale but the overall durability of the mineral is much more than that because it has a strong molecular structure.

Treatments & Enhancements

Several gemstones go through different processes of treatment when they are being refined. The processes involved are usually done in order to improve either the color or the overall integrity of the stone, based on how it is needed. The most common form of enhancement to gemstones is heat treatment. It can be used to affect the color of some gemstones that are susceptible to heat. The different treatments can have their own impact on a minerals overall durability depending on the qualities of that particular stone.

Final Thoughts

It is important to be familiar with mineral durability if you have an interest in gemstones. Knowing this information will help you to find not only the most beautiful stones but the ones that will stand the test of time.

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