A crystallographic analysis of hexagonal poudretteite (KNa2B3Si12O30, symmetry P6/mcc) and cubic pollucite (CsAlSi2O6, Ia(Formula presented.)d) has revealed characteristic features of two versions of energetically stable atomic configurations, which are abundant among natural and synthesized inorganic compounds. These are structures with a minimum number of parameters (not fixed by the symmetry of basis-atom coordinates) and minimum volumes V* of independent parts of unit cells. The structures of silicates with a large number of tetrahedral cations exhibit a symmetry of glide planes and screw axes, which provides both stability and close packing of topologically connected fragments (templates) of these structures.
- CRYSTALLOGRAPHIC ANALYSIS