A term often used when discussing the durability of gemstones is ‘toughness’. Not to be confused with hardness (which relates to the surface ability of the gem to withstand scratches - see Mohs scale), the toughness of a gem has more to do with its ability to withstand hard impact and its resistance to fracturing. The toughness of a gem is just as important as its hardness, and knowledgeable Lapidarists will always consider the gem’s toughness when deciding what type of cut to apply. The less tough a gem, the more likely it is to have truncated corners and to be step cut rather than brilliant cut. Jewellers also have to be aware of which gemstones need to be better protected when setting them in jewellery.
To understand toughness better, think about Diamonds: they are the hardest mineral known to man, yet they are not the toughest, meaning they are just as prone to chipping and fracturing as several other gemstones.
