You sometimes hear jewellers mention something called the Mohs scale in reference to the hardness of a gemstone. Hardness is one of the measures that contributes to overall durability in a piece of jewellery and it helps to understand how well your jewellery will wear over time.
The Mohs scale was created by German minerologist Freiderich Mohs in the early 19th century. The scale indicates a mineral’s resistance to scratching (going forward I’ll refer to gemstones rather than minerals, as this is an article about jewellery) . The the lowest number on the scale indicates a gemstone that can be scratched by any other gemstone. The highest number indicates a gemstone that can scratch all others. Essentially a gemstone can scratch any other gemstone with a lower number than itself on the scale and likewise can be scratched by any gemstone with a higher number on the scale. So for instance if you have a Topaz and an Amethyst, you can scratch the amethyst with the topaz, but not the other way around.
Hardness therefore contributes a lot towards overall wearability of a piece of gemstone jewellery. However it is not the only thing to consider. There is also the concept of tenacity. Tenacity refers to how well a gemstone reacts to impacts. So for example, a Diamond is a 10 on the Mohs scale so virtually unscratchable, however if you hit it with a hammer it might shatter. Now most of you aren’t going around hitting your gemstones with a hammer but you may occasionally knock your jewellery against a surface that is harder than the gemstone which could in turn chip it. Diamonds are susceptible to chipping if they sustain hard knocks especially around the girdle (the fine edge of the gemstone)
This brings us to the next consideration and this is wearability. Wearability is more about you and how you wear your jewellery. So for instance if you have an opal ring, consider how you are wearing it. Is it set in a ring? Earrings? Pendant etc? An Opal is a very soft stone, softer in fact than dust which contains minerals such as quartz (7 on the Mohs). So even simple actions like putting your hands into your pockets or handbag may scratch the gemstone and over time the gemstone will become dull. Thus the wearability of opal is relatively poor. Ideally wear your opals only occasionally when set in rings and/or make sure they are set in protective settings such a bezels. Earrings and pendants are a much better choice as they are seldom subjected to rubbing in the same way as rings or bracelets.
One last consideration is cleavage. No, not that kind! The kind found in gemstones. These are planes along which a gemstone can be “cut” to form facets. Think about cleavage similar to the grain in wood. If you want to split wood, you split is along the grain as it will peel apart quit easily. But if you try to split it against the grain, it’s very difficult (the origin of “going against the grain”!). Technically, cleavage is the result of weak atomic bonds in the structure of the gemstone. So for instance, a topaz is an 8 on the mohs but it has perfect cleavage and is easily split which is reat for facetting. But you should never clean your topaz in an ultrasonic cleaner as the high vibrations may cause it to spit along its cleavage.
It’s worth a note, that pure, unalloyed gold and silver are roughly 2.5 – 3 on the Mohs which is why they are almost always alloyed to other harder metals to make them stronger for wear in jewellery.
There you have it! A little knowledge can help you care for your jewellery to ensure it lasts a lifetime. The Mohs scale helps you understand how scratch resistant your gemstone jewellery is.
Any questions? Drop them into the comments below! Thank for reading!