CaMg 2 (SO 4 ) 3 , sulfates, solid-/gas-phase reactions, structure elucidation, X-ray diffraction. PACS 61.10.Nz, 61.66.Fn Crystals of the double sulfate CaMg 2 (SO 4 ) 3 have been obtained by solid-state reactions of stoichiometric amounts of anhydrous CaSO 4 and MgSO 4 in sealed and evacuated silica tubes with chlorine gas as mineraliser. The crystal structure was determined from single crystal X-ray diffractometer data [P6 3 /m, Z = 2, a = 8.3072(4), c = 7.3057(8) ร
, R[F 2 > 2ฯ(F 2 )] = 0.0317, wR(F 2 all) = 0.0785, 476 structure factors, 33 variable parameters] and consists of distorted [CaO 6 ] octahedra (3 symmetry), [MgO 6 ] octahedra (3 symmetry) and SO 4 tetrahedra (m symmetry) as single building units. The structure is made up of 1 โ [CaO 6/2 ] chains of face-sharing [CaO 6 ] octahedra that extend parallel to [001], alternating with columns of face-sharing [MgO 3/1 O 3/2 ] 2 dimers. Both types of chains are linked via corner-sharing with SO 4 tetrahedra into a threedimensional framework structure. Although the compound crystallizes in a new structure type, it is topologically related to the NaZr 2 (PO 4 ) 3 (Nasicon) structure, and a comparative discussion between both structural arrangements is given.