Many believe a diamond is the most durable gem since it is the hardest, a 10 on Moh’s scale, however there’s more to durability than hardness. For example diamond and topaz are both hard but exhibit perfect cleavage, meaning they can easily split by a single blow. Corundum gemstones aren’t as hard as diamond, but have no cleavage, making them more durable, even if they’re not as hard as diamond. Feeling a little confused? Let’s learn what makes a gemstone durable.
What Does Gemstone Hardness & Toughness Mean?
Hardness defines how well a gemstone resists scratches and abrasions which is an important consideration for wearability. Moh’s Hardness is a scale used to measure the scratch resistance of some readily available stones, not to be confused with the toughness of them. A diamond is the hardest natural material in the world, but it’s also very brittle. There’s an old saying among gemologists: if you hit a diamond with a hammer it’ll shatter into a dozen pieces, hit a piece of quartz and it’ll split in two, hit a piece of jade and it’ll ring like a bell! How is this possible?!
Hardness depends on the bonds that hold the atoms together within a crystal structure. This bonding is evident in the ease with which the layers of atoms at a surface can be separated by applying pressure with a sample of another material. If the second material is harder than the first, it’ll leave a furrow or scratch that represents the breaking of millions of atomic bonds on a microscopic scale. Therefore the hardness of a mineral is specifically its “scratch-ability” so every mineral can be ranked based on the others minerals it can scratch.
Toughness is a mineral’s resistance to breaking and chipping, which is often measured as its tenacity or resistance to blows. For example a diamond can’t be scratched by steel, but a blow by a hammer can shatter one. Toughness is rated from poor, fair, good, excellent to exceptional. Although diamond is the hardest natural substance on earth, it’s rated ‘good’ for toughness; corundum (ruby, sapphire) however are the most durable stones measuring 8 on Moh’s Scale but considered ‘excellent’ for toughness.
Cleavage has to do with how strongly the molecules of a gemstone bind to each other, much like wood grain (you can easily split a piece of wood along the grain, but going across the grain is much more difficult). Diamonds have perfect cleavage meaning they can easily split along cleavage planes, it also means they can chip or shatter with wear. On the other hand, quartz is less hard than diamond but can take a lot of banging about without damage.
How to Choose Wearable Gemstone Jewelry
The stability of a mineral refers to its resistance to chemicals, heat, light, temperature and humidity. Despite how hard a diamond is, extreme temperature changes can fracture it. Opals may crack in low humidity, while prolonged light exposure can discolor citrine, amethyst, and topaz as well as pearls and other organic gems. This is why gemstones should always be stored properly and separately to avoid damage and to be mindful of what we may be exposing our jewelry to on a daily basis (showering, using hair spray or perfume, household cleaners, etc).
Assuming you don’t bash your jewelry with a hammer, scratching is the most frequent hazard- how many times do you put your hands inside pockets, purses, glove compartments, desk drawers, etc everyday and what does your jewelry brush against? An opal with a hardness of 6 will be rapidly covered with fine scratches and lose its polish if worn everyday as a ring stone, but a ruby with a hardness of 9 will remain bright and lustrous because it’s harder than most of the abrasive particles that contribute to wear.
A 7 or higher on Moh’s scale usually indicates a gem is hard enough for normal jewelry use, but this is a guideline not a rule. Jewelry settings are another factor for gemstone wearability. Rings probably receive more abuse than any other form of jewelry, so if you were considering a stone with a poor wearability grade you could use the stone for a different piece of jewelry like a necklace or earrings, or surround it in a protective setting.
If you’re wondering which stones are best for everyday wear such as an engagement ring, sapphire, ruby and diamond are some wonderful choices, just remember that hardness alone isn’t a measure of a stone’s wearability. If you have questions or want help designing the perfect piece of jewelry to match your lifestyle give us a call at 303-385-8449 or click here to schedule a consultation.