Summary: Further data are presented on the properties of natural and synthetic members of this series. Cell constants have been determined for over 50 specimens across the composition range; the activation energy for a low-high transformation in an intermediate hyalophane has been evaluated as 101·5 ± 5·0 kcal/mole; additional single crystal studies have revealed complexities not previously reported.

Although there remain many detailed problems to be resolved, the present studies allow some suggestions concerning the nature of the relationships within the series. Problems of nomenclature and subsolidus relations are discussed together with some structural implications.