Unlike crystals, the description of Luminous Stones does not explicitly state "hardness"; these stones seem to excel only in their powerful lethal force.
In fact, most of the magic related to Luminous Stones obtained in the Sain Dungeon consists of throwing Luminous Stones in varied shapes and forces to kill enemies.
But this indirectly proves that Luminous Stones are indeed strong in killing enemies; they are extremely "sharp."
As for crystals, their introduction already includes "hardness." While the number of magics related to crystals isn't large, each one exploits this trait to the fullest.
Originally, in Hades' early research, the fusion of these two different types of stones resulted in magic that combined both properties, but with weakened versions. Simply put, the Luminous Stone Crystals he created had neither the strong attack power of Luminous Stones nor the hardness of crystals, making them quite mediocre.
