The phenomenon you are referring to is called polymorphism. Polymorphism is the ability of a substance to exist in different crystal structures or forms while maintaining the same chemical composition. In the case of sodium chloride (NaCl), it can exhibit two common polymorphic forms: cubic (also known as the rock salt structure) and octahedral (also known as the cesium chloride structure). These different forms of sodium chloride result from variations in the arrangement of the sodium and chloride ions within the crystal lattice.