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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.

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A Sterling Silver bracelet set with tough Tanzanite.