The ability of a gemstone to remain intact, withstand force (pressure) and resist breaking or chipping is known as toughness. Determined by a substance's atomic and chemical structure, toughness can vary directly within a gemstone.
While both Moissanite and diamond are rated excellent in toughness, Moissanite has a different atomic structure than diamond which does not have a direction of cleavage (which sometimes is considered as a direction of structural weakness) like diamond. Simply said, Moissanite outranks diamond in overall toughness.