data_global _amcsd_formula_title 'Na8Si[Si6O18]' loop_ _publ_author_name 'Fleet M E' _journal_name_full 'American Mineralogist' _journal_volume 83 _journal_year 1998 _journal_page_first 618 _journal_page_last 624 _publ_section_title ; Sodium heptasilicate: A high-pressure silicate with six-membered rings of tetrahedra interconnected by SiO6 octahedra: (Na8Si[Si6O18]) ; _database_code_amcsd 0002009 _chemical_formula_sum 'Na8 Si7 O18' _cell_length_a 7.180 _cell_length_b 7.180 _cell_length_c 7.180 _cell_angle_alpha 87.26 _cell_angle_beta 87.26 _cell_angle_gamma 87.26 _cell_volume 368.916 _exptl_crystal_density_diffrn 3.009 _symmetry_space_group_name_H-M 'R -3' loop_ _space_group_symop_operation_xyz 'x,y,z' '-z,-x,-y' 'y,z,x' '-x,-y,-z' 'z,x,y' '-y,-z,-x' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z Na1 0.23630 0.23630 0.23630 Na2 0.00000 0.50000 0.50000 Na3 0.50000 0.00000 0.00000 Si1 0.00000 0.00000 0.00000 Si2 0.27190 0.73960 0.27150 O1 0.21290 0.54510 0.21280 O2 0.16900 0.91810 0.16920 O3 0.23460 0.76530 0.49950 loop_ _atom_site_aniso_label _atom_site_aniso_U_11 _atom_site_aniso_U_22 _atom_site_aniso_U_33 _atom_site_aniso_U_12 _atom_site_aniso_U_13 _atom_site_aniso_U_23 Na1 0.01609 0.01609 0.01609 0.00000 0.00000 0.00000 Na2 0.02280 0.01760 0.02001 -0.00253 -0.00317 0.00215 Na3 0.01406 0.01469 0.02799 0.00076 -0.00190 -0.00127 Si1 0.01140 0.01140 0.01140 0.00000 0.00000 0.00000 Si2 0.01203 0.01317 0.01292 -0.00063 -0.00025 -0.00051 O1 0.02305 0.01722 0.02115 -0.00203 -0.00684 -0.00139 O2 0.01722 0.01684 0.01355 0.00013 -0.00279 0.00063 O3 0.02179 0.02064 0.01368 0.00253 0.00076 -0.00051