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 = ambient Note: y(F6) and z(F6) corrected ; _database_code_amcsd 0013481 _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 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 0.00030 0.50000 Na2 -0.00270 0.25000 0.75000 Mg 0.25000 0.00060 0.00000 Al 0.00000 0.25000 0.25000 F1 0.00000 0.00000 0.88630 F3 -0.00160 0.16480 0.47090 F5 0.18300 0.13590 0.18180 F6 0.31500 0.63880 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 0.01770 0.01920 0.05530 0.00000 -0.00450 0.00000 Na2 0.02190 0.03330 0.01490 0.00000 0.00000 0.00950 Mg 0.00740 0.00630 0.00710 0.00000 -0.00080 0.00000 Al 0.00780 0.00700 0.00750 0.00000 0.00000 -0.00180 F1 0.00780 0.01910 0.01270 -0.00290 0.00000 0.00000 F3 0.01840 0.01590 0.00950 0.00350 0.00040 0.00140 F5 0.01450 0.01280 0.01800 0.00980 0.00090 -0.00610 F6 0.01150 0.01350 0.01550 -0.00320 0.00250 -0.00830