MODELLING OF THE SELF-ORGANIZATION PROCESSES IN SILICATE CRYSTAL FORMING SYSTEMS. G.D. Iljushin and L.N. Demianets, Institute of Crystallography, RAS, Moscow, Russia
The model of kinetic phase transition of a disorder-order type were suggested for the crystallization in silicate-containing systems under hydrothermal conditions. The crystal-forming system from SiO4-tetrahedra and MOn-polyhedra (n=4 for Al, n=5 for Ti, n=6 for Zr) was choosen as a model system.
The elements of the theory of non-closed packings consisting of octahedra M06 and tetrahedra SiO4 were developed (only one common apex was permitted for the connection of tetrahedron and octahedron, the number of tetrahedra was equal to the number of octahedra). The variants of the formation of MT chains and MT-layers with different topology and symmetry were found.
On the base of the theoretical ideas on the silicate formation, the algoritm of matrix assembling of the known crystal structures of zirconosilicates, titanosilicates and aluminosilicates was determined. The analysis of the symmetry data for silicates was carried out using the author's method of crystal strucrural intersections of space groups of symmetry. This method provides a possibility to identify the channels of structure evolution depending on growth conditions. In the framework of the model, the mechanism of the Si-radical formation from isolated SiO4- tetrahedra (chains, rings, layers, framework) is described.