Rock salt (NaCl) is ionic crystalline compound having Na+ and Cl- ions Coordination number for an ion is the number of oppositely charged ions around it. So, it is 6. NaCl has fccstructure, each sodium ion is surrounded by 6 chlorine ions. A perovskite is any material with the same type of crystal structure as calcium titanium oxide (CaTiO3), known as the perovskite structure. The ideal cubic structure has the B cation in 6-fold coordination, surrounded by an octahedron of anions, and the A cation in 12-fold cuboctahedral coordination.