Tough as Gemstones

The hardness of a gemstone is measured by the resistance it has to being scratched by another material, widely measured using the Mohs scale of hardness. The toughness of a gemstone is quite different but also important when considering using gemstones in jewellery.

The toughness of a gemstone is the material’s resistance to chipping, breaking or fracturing. The toughness of gemstones can refer to how brittle a material is – how it reacts to pressure and whether the material will shatter or absorb energy – some gemstones when hit with enough force will shatter and crumble, and some will chip. Few may be hardly affected by the impact.

The chance of a gemstone fracturing or chipping when knocked at a specific angle can depend on the gemstone’s structure. The crystal structure of a gemstone can determine the gemstone’s cleavage; the plane at which the material will naturally flake or fracture with impact at the right point, producing a clean flat surface. Many materials can have multiple cleavages – which means that the stone can chip or break at multiple angles – but not necessarily that it is weaker or more likely to break.

Crystal formed gemstones have lines of weakness or inclusions developed when the material is formed, which make the stone more fragile, and some stones of the same material can be more likely to fracture than others. Natural inclusions can weaken gemstones and emeralds are a good example. Emerald is relatively high on the mohs hardness scale, 7.5 – 8, but in terms of toughness, it is rated as poor to fair and can be chipped and fractured easily because it naturally contains multiple inclusions, so if the stone is knocked it is likely to break along any of the inclusions. Gemstones can often have these contradicting properties of hardness and toughness. Another example is Jade which is considered the toughest of gemstones because of its interlocking fiber crystal structure, but is only around 6.5 on the Mohs scale.

The cut of a stone can make it less likely to fracture. Gemstones are cut to reduce the chance of the stone chipping or breaking- although a very included stone will be more likely to break even if it is cut well. Some stones are fragile and have a low toughness rating, for example opal, which has a high water content which weakens the structure of the stone, moonstone and emeralds are not necessarily suggested for engagement rings but when used in jewellery like pendants and earrings, and when looked after, they could last a lifetime.

Sapphire and Ruby (corundum) is one of the most durable gemstones with a Mohs hardness of 8, an ‘excellent’ toughness rating and no cleavage. Diamonds are the hardest of all gemstones but their toughness rating is ‘good’. Corundum and diamond are therefore some of the most durable gemstones for everyday jewellery like engagement rings.

All of the gemstones between diamond and opal can be beautiful stones to use in jewellery, it’s just a case of designing the most suitable form of jewellery to make the stone wearable for a lifetime, take a look at our gemstone engagement rings to see all the colours and styles.

There is an old saying that, if you hit a diamond with a hammer, it will shatter into a dozen pieces. If you hit a piece of quartz, with a hammer it will split in two. Hit a piece of jade with a hammer and it will ring like a bell!