data_global _chemical_name_mineral 'Weberite' loop_ _publ_author_name 'Knop O' 'Cameron T S' 'Jochem K' _journal_name_full 'Journal of Solid State Chemistry' _journal_volume 43 _journal_year 1982 _journal_page_first 213 _journal_page_last 221 _publ_section_title ; What is the true space group of weberite? Sample: I2mb refinement, T = 133 K Note: z(F6) corrected ; _database_code_amcsd 0013484 _chemical_compound_source 'Ivigtut, Greenland' _chemical_formula_sum 'Na2 Mg Al F7' _cell_length_a 7.051 _cell_length_b 9.968 _cell_length_c 7.285 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 90 _cell_volume 512.022 _exptl_crystal_density_diffrn 2.987 _symmetry_space_group_name_H-M 'I 2 m b' loop_ _space_group_symop_operation_xyz 'x,y,z' '1/2+x,1/2+y,1/2+z' 'x,1/2+y,1/2-z' '1/2+x,+y,-z' 'x,-y,z' '1/2+x,1/2-y,1/2+z' 'x,1/2-y,1/2-z' '1/2+x,-y,-z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z Na1 0.25360 0.00000 0.49580 Na2 0.00000 0.25000 0.75000 Mg 0.25200 0.00000 0.99920 Al 0.00140 0.25000 0.25000 F1 0.00130 0.00000 0.88620 F3 0.00230 0.16440 0.47130 F5 0.18750 0.13820 0.18220 F6 0.31850 0.13670 0.82090 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 0.01210 0.01220 0.04320 0.00000 -0.00330 0.00000 Na2 0.01420 0.02530 0.01230 0.00000 0.00000 0.00700 Mg 0.00520 0.00470 0.00780 0.00000 0.00050 0.00000 Al 0.00530 0.00520 0.00780 0.00000 0.00000 -0.00120 F1 0.00540 0.01400 0.01180 0.00000 0.00130 0.00000 F3 0.01270 0.01110 0.01000 -0.00120 -0.00100 0.00000 F5 0.00870 0.00880 0.01340 0.00020 -0.00010 -0.00300 F6 0.00950 0.00950 0.01540 0.00410 0.00300 -0.00450