The crystal structure and chemical composition of pollucite

The structure of pollucite from Rumford, Maine has been determined and refined. The space group is Ia 3 d with cell edge a = 13.69 Å. The structure was investigated using 213 independent reflection intensities measured on a single crystal diffractometer. Pollucite has the analcime framework with the cesium atoms occupying the large voids in the framework, as initially suggested by N áray -S zabó . The water molecules occupy the large voids of this same set which are not occupied by the cesium atoms. The sodium atoms are located in equipoint 24 c , at ¼ ⅛ 0, in the positions between the water molecules. The water molecules and the sodium atoms occupy the same positions as they do in analcime, but they occur only in randomly distributed clusters of atoms whose outer members are restricted to water molecules. The final structure was refined by least squares to an R value of 0.050 for all reflections. The chemical composition of pollucite can be expressed by a general formula similar to: Cs x Na y Al x+y Si 48− x − y · O 96 (16− x ) H 2 O, in which 2 y ⩾ 16 − x ⩾ y .