data_global _chemical_name_mineral 'Gypsum' loop_ _publ_author_name 'Pedersen B F' 'Semmingsen D' _journal_name_full 'Acta Crystallographica, Section B' _journal_volume 38 _journal_year 1982 _journal_page_first 1074 _journal_page_last 1077 _publ_section_title ; Neutron diffraction refinement of the structure of gypsum, CaSO4*2H2O ; _database_code_amcsd 0020895 _chemical_compound_source 'Hampshire, England' _chemical_formula_sum 'Ca S O6 H4' _cell_length_a 5.679 _cell_length_b 15.202 _cell_length_c 6.522 _cell_angle_alpha 90 _cell_angle_beta 118.43 _cell_angle_gamma 90 _cell_volume 495.153 _exptl_crystal_density_diffrn 2.310 _symmetry_space_group_name_H-M 'I 1 2/a 1' loop_ _space_group_symop_operation_xyz 'x,y,z' '1/2+x,1/2+y,1/2+z' '-x,y,1/2-z' '1/2-x,1/2+y,-z' '1/2+x,1/2-y,z' '+x,-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 Ca 0.50000 0.07967 0.25000 S 0.00000 0.07705 0.75000 O1 0.96320 0.13190 0.55047 O2 0.75822 0.02226 0.66709 OW 0.37960 0.18212 0.45881 H1 0.25112 0.16158 0.50372 H2 0.40458 0.24275 0.49217 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 Ca 0.02070 0.02580 0.01950 0.00000 0.00810 0.00000 S 0.01900 0.02040 0.01920 0.00000 0.00860 0.00000 O1 0.02620 0.02790 0.02430 -0.00110 0.01230 0.00440 O2 0.02220 0.02700 0.02540 -0.00460 0.00920 0.00080 OW 0.03910 0.02940 0.03910 0.00010 0.02530 -0.00380 H1 0.05990 0.04640 0.06320 -0.00120 0.04320 0.00180 H2 0.05960 0.03830 0.07140 -0.00390 0.03840 -0.00850