From structure topology to chemical composition. XI. Titanium silicates: crystal structures of innelite-1T and innelite-2M from the Inagli massif, Yakutia, Russia, and the crystal chemistry of innelite.

The crystal structures of two polytypes of innelite, ideally Ba4Ti2Na2M2+Ti(Si2O7)2[(SO4)(PO4)]O2[O(OH)] where M2+ = Mn, Fe2+, Mg, Ca: innelite-1T, a 5.4234(9), b 7.131(1), c 14.785(3) Å, ? 98.442(4), ? 94.579(3), ? 90.009(4)°, V 563.7(3) Å3, space group PFormula, Dcalc. = 4.028 g/cm3, Z = 1; and innelite-2M, a 5.4206(8), b 7.125(1), c 29.314(4) Å, ? 94.698(3)°, V 1128.3(2) Å3, space group P2/c, Dcalc. = 4.024 g/cm3, Z = 2, from the Inagli massif, Yakutia, Russia, have been refined to R values of 8.99 and 7.60%, respectively. Electron-microprobe analysis gave the empirical formula for innelite as (Ba3.94Sr0.06)?4.00(Na2.16FormulaFormulaMg0.15Ca0.10?0.04)?3(Ti2.97Nb0.02Al0.02)?3.01Si4.01(S1.02P0.81?0.17)?2H1.84O25.79F0.21 which is equivalent to (Ba3.94Sr0.06)?4.00(Ti1.97Nb0.02Al0.02)?2.01(Na2.16FormulaFormulaMg0.15Ca0.10?0.04)?3Ti(Si4.01O14)[(SO4)1.02(PO4)0.81(OH)0.51H2O0.17]O2[(OH0.99F0.21)?1.20O0.80], calculated on the basis of 26 (O + F) anions, with H2O calculated from structure refinement. The crystal structure of innelite is a combination of a TS (titanium silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral) and exhibits linkage and stereochemistry typical for Ti-disilicate minerals of Group III (Ti = 3 a.p.f.u.): two H sheets connect to the O sheet such that two (Si2O7) groups link to the trans edges of a Ti octahedron of the O sheet. The I block contains T sites, statistically occupied by S and P, and Ba atoms. In the structures of innelite-1T and innelite-2M, TS blocks are related by an inversion centre and a cy glide plane, respectively. HRTEM images show a coherent intergrowth of the two polytypes, together with an as-yet unidentified ~10 Å phase.