Symmetry and structural relationships among ABW-type materials

The symmetry relationships among zeolite-type ABW compounds are described i n terms of the reductions of symmetry from the highest possible topological symmetry in space group Imam to eight possible subgroups. This family of c ompounds, also known as Icmm-type compounds. covers a wide range of chemica l compositions. The distortion modes inducing the lowering of symmetry are described based on rotation and ordering processes. Atomic site relationshi ps with their evolution from the aristotype are given for the recently desc ribed monoclinic P112(1)/n structures with an ABW-type framework.