Toughness refers to how well a gemstone can withstand external mechanical stress, such as impacts from falling or hammering, without breaking, chipping and cracking. Toughness is not necessarily identical to hardness; a diamond is the hardest minerals in nature but not the toughest. Jadeite and nephrite may not be as hard as diamonds, but they can withstand hammering without breaking. This is because they have interweaving fiber bundle-like structures that give the minerals their toughness.