“…Comparison of the crystal structure of CaMg 2 (SO 4 ) 3 with that of the isoformular (both compounds have the general formula AB 2 (CX 4 ) 3 ) NaZr 2 (PO 4 ) 3 (Nasicon) reveals a topological relationship. The unit cell of the NaZr 2 (PO 4 ) 3 structure (Z = 6, R3c, a' ≈ 8.81, c' ≈ 22.75 Å) [14] is tripled with a' ≈ a and c' ≈ 3c in respect to the unit cell of CaMg 2 (SO 4 ) 3 (note that there is no direct group-subgroup relation between space groups R3c and P6 3 /m), and the Ca, Mg and S atoms are replaced by Na, Zr and P, respectively. (Fig.…”