One of the terms associated with gemstones is toughness. Usually when gemstones are defined as durable, they include two distinct traits, hardness and toughness. A mineral’s hardness is its ability to resist scratches or abrasions. A mineral’s toughness is its ability to resist being fractured.
Toughness is extremely important to many jewelry wearers because if the gemstone is purchased to be worn on a daily basis, it may become damaged either by impact or by it being chipped. A tough mineral will resist fractures.
Usually diamonds are very hard, but they can certainly chip and fracture in normal day to day wear and tear. Usually the cleavage has partly to do with how tough a gemstone is. For instance, if a crystal is formed in a certain way, it can make it prone to chipping or fracturing. Another way a gemstone can either be more prone to chipping or fracturing is by how it is cut. For instance, a diamond having lots of facets may be more prone to chipping, while a diamond that is cut with less facets may be less prone.
It is also important to note that jewelry pieces can make a gemstone more prone to damage. If you like a gemstone that is not very tough such as Opal, you might want to consider wearing it in a much more secure manner, for instance, as a charm instead of a ring. Just because a gemstone is less tough, shouldn’t stop you from wearing it, just use more caution.