Developed by German mineralogist, Friedrich Mohs, in the 1800s, this scale is used by gemologists to classify a gem’s resistance or the difficulty or ease that one mineral can be scratched by another. The scale ranges from values of one to ten with one being the least resistant to scratching and ten being the hardest and most resistant.
In 1801, Mohs was hired by a wealthy banker to curate and identify his collection of minerals. At the time, minerals were largely classified by their chemical composition, but this approach wasn’t very consistent, and Mohs set out to find a more accurate method. Eventually he came up with a set of ten values of hardness that could be determined with a relatively straightforward, and now infamous, scratch test.
Diamonds score a ten on the Mohs scale and this durability is one of the reasons why they make an excellent choice for engagement rings that will be worn every day and be exposed to general wear and tear. The softest mineral on the scale is Talc at one – interestingly it is softer than pencil lead (1.5) and fingernails (2.5)!
While the scale is renowned for both its simplicity and accuracy, it does not always factor in other elements of gemstone structure. For example, emeralds have many inclusions within the stone which can weaken the structure and make them more susceptible to scratching and chipping. Another important thing to note is that the scale is not linear. In other words, a diamond is actually four times harder than a sapphire stone. Sapphire, which is next up on the scale from topaz, is only two times harder. The scale also doesn’t account for durability or stability.
Hardness vs. Durability vs. Stability
Hardness defines how well a stone resists scratches and abrasions. As mentioned earlier, this is an important consideration for the wearability particularly for rings and bracelets
Toughness or durability is the mineral’s resistance to chipping or breaking - said plainly, its resistance to blows. A diamond, for example, can’t be scratched by steel, but if you hit it with a hammer and it can shatter (who would ever do that?!)
Stability means how resistant the mineral is to things like heat, light, humidity, and chemicals. Even though diamonds are as hard as minerals come, extreme changes in temperature can fracture them. Another example is prolonged light exposure may cause discoloration to minerals like citrine, pearls, and amethyst.
What does this all mean for diamond and gemstone owners?
You should be aware of how your jewelry is worn and stored. As you learned from the Mohs Hardness Scale, with the exception of diamonds, gemstones can be scratched by other minerals. And even though diamonds can’t be scratched by other gemstones, they can scratch each other. This should be kept in mind when stacking wedding bands and engagement rings. Any friction between exposed stones and metal can lead to scratches and irreversible damage. Likewise, when storing jewelry, each piece should be separated to avoid friction.