KNa2Tm[Si8O19] · 4H2O, a new layered silicate related to rhodezite-shlykovite-delhayelite-umbrianite-guenterblassite-hilleshaymite: Topology-symmetry analysis of the OD-family and structure prediction

• Published in: Crystallography reports 2014-07, Vol.59 (4), p.513-522
• Main Authors: Belokoneva, E. L., Topnikova, A. P., Dimitrova, O. V., Volkov, A. S.
• Format: Article
• Language: English
• Subjects: Crystallography and Scattering Methods; Physics; Physics and Astronomy; Structure of Inorganic Compounds
• ISSN: 1063-7745; 1562-689X
• DOI: 10.1134/S1063774514040051

Crystals of a new silicate KNa 2 Tm[Si 8 O 19 ] · 4H 2 O, space group P 12/ m 1 (the chemical formula was determined in the course of structure solution), are obtained under hydrothermal conditions. KNa 2 Tm[Si 8 O 19 ] · 4H 2 O is the first synthetic representative of the family, which contains the following well-known and recently discovered minerals: rhodezite, delhayelite (fivegite, hydrodelhayelite), mountainite, shlykovite (cryptofillite), and guenterblassite (umbrianite, hilleshaymite). A crystal chemical analysis within the extended OD theory revealed the similarity of the structures of the family, including the new simplest representative and the factors responsible for structural diversity, namely, different symmetry of sheets of octahedra connected with layers of tetrahedra, which are distinguished in all the structures, and different patterns of symmetry relation between the sheets. Hypothetic structures with a higher degree of disordering are deduced. Crystals with these structures can be found in nature or obtained synthetically.