Mohs Scale: Understanding Gemstone Hardness
We have all heard that a diamond is the hardest gemstone. Diamonds are among the hardest naturally occurring materials in the world. If an unknown gemstone is easily scratched, it is very unlikely to be a diamond. Hardness is an attribute that sets diamonds apart from other gemstones, but how do we determine how hard a gemstone is? The answer is the Mohs Scale.
What is the Mohs Scale
The Mohs Scale was devised by Friedrich Mohs, a German geologist and mineralogist in 1812. How does it work? Friedrich Mohs chose 10 minerals and ranked each of them on their hardness from 1 to 10 – 1 being the softest and 10 the hardest. To find out the hardness of one gemstone over the other, a simple test is carried out. All one needs to do is create a scratch from one sharp edge of the gemstone on another gemstone’s flat surface.
Understanding the Mohs Scale
Friedrich Mohs in his test also mentioned a few common objects that are easily available to identify the hardness of all ten of the minerals, starting with the softest to the hardest:
Talc ranks 1st and gypsum ranks 2nd on the Mohs Scale. These two are the softest minerals and can be easily tested by scratching on them with your fingernail which has a Mohs hardness of 2.5.
Next on the scale would be calcite which ranks 3rd and the most common object to determine its hardness would be the most easily found copper penny which has a Mohs hardness of 3.5.
Fluorite ranks 4th and apatite ranks 5th being comparatively much harder than the above minerals. Their hardness can easily be determined by a sharp object available in every household - a knife with a Mohs Hardness of 5.5.
The next mineral on the Mohs Scale is orthoclase which has the 6th rank.
Gemstones on the Mohs Scale
If we keep going in order of softest to hardest, pearls get us started coming with a hardness of 4 on the Mohs Scale. Following pearls is turquoise at a hardness level of 5. Next up are amethysts, peridots, quartz and garnets all sharing a hardness level of 7. The common object that helps us determine their rank would be steel nails as they have a Mohs hardness of 7.5. Emeralds and topaz feature next with a hardness level of 8 preceeding rubies and sapphires at hardness level 9. Diamonds of course are the hardest with a ranking of 10. There is no other natural element on Earth that is harder than diamond. Therefore, you can see how the Mohs Scale is used to offer a helpful framework to identify gemstone hardness.
Why is the Mohs Scale important in Jewelry
The Mohs Scale lets us know that diamonds (10) are harder than sapphires and rubies (9) which are harder than topaz and emeralds (8) which are harder than amethysts, peridots, quartz and garnets (7) which are harder than turquoise and lapis lazuli (5) which are harder than pearls (4).
So you would want to be more careful when wearing gemstones with a lower hardness on the Mohs Scale to avoid scratches. You may decide to wear certain gemstones less frequently and choose gemstones with a higher hardness on the Mohs Scale for jewelry you wear regularly. When storing your jewelry, make sure to keep your pieces away from each other so your diamonds don’t scratch your other gemstones.