When selecting gemstones for jewellery it is very important to understand the difference between gemstone hardness and gemstone toughness. Both of these factors contribute to a stones durability, but the effects of each property can have huge consequences on gemstones.
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Firstly, gemstone hardness. Many people have heard of the MOHS scale. It is a mineral scale of gemstone hardness that starts at 1 being the softest and 10 the hardest. It was discovered by scratching one mineral with another and seeing what could scratch what.
Diamond is by far the hardest gemstone. Diamond can only be scratched by another Diamond. The MOHS scale above shows where different minerals sit in relation to each other. When looking at the chart, keep in mind that any gemstone to the left of another gemstone can scratch it. For example, Corundum (9) can scratch Topaz (8), Quartz (7) ect but Quartz cannot scratch Corundum.
The most important number on this scale is Quartz (7). The atmosphere contains minute particles of Quartz and Feldspar that float around and settle on surfaces such as out precious jewellery. When creating jewellery that is going to be wore every day, it is important to remember that this dust will settle on your stones and can scratch the gemstones if proper care is not taken when cleaning.
As a general rule, it is preferred to use gemstones with a MOHS of 7 or higher to avoid this scratching issue. If you have a Topaz ring, even if Quartz and Feldspar settle on the ring, it will not be able to scratch it because Topaz is harder than both Quartz and Feldspar.
Mineral Hardness In Everyday LifeIn everyday life there are items around you that use the hardness of minerals. One of the best examples is in mobile phone screens. These screens are often called glass, but they are not. Colorless Synthetic Sapphire is used for the screen because it is the second hardest mineral behind Diamond. Synthetic Sapphire is also very easy to manufacture. It is made of Aluminium Oxide and is created by pouring two powders into a furnace to create a boule.
The next issue is gemstone toughness. Toughness is very important because it is the ability of a gemstone to withstand mechanical shock. that is accidentally bumping it against something. In this case, Diamond is not the toughest gemstone, in fact it can be very brittle. Jadeite Jade is by far the toughest gemstone. It is extremely hard to break and can worn for many years without a crack appearing.
A very important factor that affects toughness is cleavage. Cleavage is a weakness at the atomic level within the gemstone that can cause it to easily break. Diamonds have cleavage, as does Kunzite and Tanzanite. Think about cleavage like splitting wood. it is very hard to split wood going at and angle to the grain, but if you split it down the center, it is a weak area and splits apart easily.
The Cullinin Diamond was cleavage to break it into a smaller more manageable piece of rough. I would not like to do this job:
These are just 2 of the very important factors that can affect gemstone durability in jewellery. It is important to always remember the magic number 7 (Quartz) and if the gem you are working with falls below this on the hardness scale then be sure to take extra precautions.