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: I2_12_12_1 refinement, T = 133 K Note: y(F6) and z(F6) corrected ; _database_code_amcsd 0013482 _chemical_compound_source 'Ivigtut, Greenland' _chemical_formula_sum 'Na2 Mg Al F7' _cell_length_a 7.050 _cell_length_b 9.979 _cell_length_c 7.297 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 90 _cell_volume 513.358 _exptl_crystal_density_diffrn 2.979 _symmetry_space_group_name_H-M 'I 21 21 21' 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' '1/2+x,-y,-z' '+x,1/2-y,1/2-z' '1/2-x,1/2-y,1/2+z' '-x,-y,+z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z Na1 0.25000 0.00010 0.50000 Na2 -0.00040 0.25000 0.75000 Mg 0.25000 0.00030 0.00000 Al -0.00110 0.25000 0.25000 F1 0.00000 0.00000 0.88610 F3 -0.00010 0.16440 0.47130 F5 0.18380 0.13620 0.18180 F6 0.31480 0.63850 0.67910 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 0.01190 0.01220 0.04400 0.00000 -0.00290 0.00000 Na2 0.01480 0.02510 0.01200 0.00000 0.00000 0.00690 Mg 0.00480 0.00480 0.00760 0.00000 0.00050 0.00000 Al 0.00560 0.00500 0.00760 0.00000 0.00000 -0.00100 F1 0.00620 0.01430 0.01160 0.00000 0.00000 0.00000 F3 0.01230 0.01090 0.01020 0.00000 -0.00200 0.00030 F5 0.00830 0.01040 0.01660 -0.00120 -0.00010 -0.00330 F6 0.01030 0.00850 0.01180 0.00530 0.00320 -0.00380