text: The crystal structure of ScS is closely related to that of sodium chloride, in that it is based on a cubic close packed array of anions. Whereas NaCl has all the octahedral interstices in the anion lattice occupied by cations, ScS has one third of them vacant. The vacancies are ordered, but in a very complicated pattern, leading to a large, orthorhombic unit cell belonging to the space group Fddd.