Mohs Hardness Scale, Explained

The Mohs scale of hardness is a qualitative scale ranging from 1 to 10 that describes the hardness of gemstones and minerals. It’s often used in geology but other industries such as milling, or fashion and apparel will refer to it frequently. When it comes to jewellery, the Mohs scale of hardness allows shoppers to know the wearability of certain pieces. Gemstones are assessed based on their ability to scratch other materials. 

Minerals are the purest form of solids found in nature. However, gemstones will generally have one or more substances within its compound structure. For example, beryl is a naturally occurring mineral structure that can produce several other gemstones like aquamarine or emeralds. Although the Mohs hardness scale was created for pure minerals, it’s often used for other compounds as well.  

Why It’s Important To Know a Stone’s Hardness

Ever wondered how diamonds got the reputation for being the hardest stone or why it’s the go-to stone for engagement rings? Diamonds are one of the hardest natural substances known, coming in at a 10 on the Mohs hardness scale. This makes them perfect for something like an engagement ring, which is worn daily. 

After purchasing a piece of jewellery, it’s important to consider how the materials will wear overtime. Certain gemstones will need additional care since they are so soft and wear easily. Things like sweat, body oils, sunscreen, and other cosmetic products can wear down materials faster than others. 

Also Read: How Sweat Affects Your Jewellery   

How To Find A Stone’s Hardness

To find out how hard a substance is on the Mohs scale of hardness, geologists take a reference mineral (substance A) and experiment scratching the unknown material (substance B). When testing a substance’s hardness, geologists monitor its scratch-resistance compared to the reference material. A third material (substance C) may be introduced to the experiment when determining an unknown material’s hardness. When making these comparisons, one of four things can happen: 

1.  If substance A can scratch substance B, then substance A is harder.
2.  If substance B can scratch substance A, then substance B is harder.
3. Substances that are of equal hardness create little to no scratching on either substance.
4. If substance A can be scratched by substance B but it cannot be scratched by substance C, then the hardness of the unknown substance is between these two items. 

For example, let’s say you wanted to know if ammolite was harder than labradorite. The labradorite (6.5 on the Mohs scale) would scratch the ammolite (3.5 on the Mohs scale) because it is harder. However, if you used BC Jade (6.5 on the Mohs scale) to scratch the labradorite, there would be little to no markings because they are relatively the same hardness.   

Popular Gemstones on the Mohs Scale

If you want a quick reference for how hard popular gemstones in jewellery are, check out our chart below.