There are three properies to durability:
Cleaving is the splitting of a diamond crystal parallel to one of its triangular, octahedral planes. While not the perfect example, compare wood, which has a single grain typically split by an axe with ease. A natural diamond crystal can only be cleaved parallel to one of the triangular octahedral faces.
As you can see from the pictures above, if you accidentally hit your diamond along the outer edge, it could be along a cleavage plane and thus be more prone to chipping. If you're a person who does a lot of hard work with your hands, you may want to consider a bezel setting or a lower setting for your diamond. Talk to your jeweler for what might work better for you; everyone can enjoy a little sparkle without the worry of chipping.
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