ИСТИНА

The comparative crystal chemical analysis of the studied silicates grumantite Na[Si2O4(OH)]xH2O, revdite Na16[Si4O6(OH)5]2[Si8O15(OH)6]x(OH)10x28H2O, megacyclite Na16K2[Si18O36(OH)18]x38H2O, intersilite (Na0.80K0.45)Na5Mn2+(Ti0.75Nb0.25)[Si10O24(OH)]x(O,OH)(OH)2x4H2O, astrophyllite K2Na{Fe7[Ti2(Si4O12)2O2F](OH)4} and minerals with close structural and chemical characteristics established structural similarity of grumantite and ussingite, megacyclite and egorovite, intersilite and palygorskite-group minerals, astrophyllite and astrophyllite-group minerals. Possible crystal chemical mechanisms of experimentally established during heating and the subsequent hydration of grumantite and kanemite transition are investigated. These mechanisms are connected with interruption of week Si-O-Si-bonds of framework and entry into the formed cavities of additional molecules of water. The batisite-like chain as well as the Na/Si-relation and the Si-O-radical formula are the general structural fragments for both minerals. The similar positions of Si-O-rings, Si-O-chains and Na-octahedral motives in the megacyclite and the egorovite structures as well as existence of potassium in the megacyclite structure, allows possible mechanisms of the structural transformation. The structure difference of the intersilite and the palygorskit-group minerals is the presence of an additional tetrahedron with polar orientation of apical vertexes in comparison of palygorskite-like structure. At the same time the heteropolyhedral framework constructed of modules TOT with large alkaline cations and water molecules in the channels is the specific feature of the intersilite as well as the palygorskite group mi nerals.