data_global _chemical_name_mineral 'Akermanite' loop_ _publ_author_name 'Yang H' 'Hazen R M' 'Downs R T' 'Finger L W' _journal_name_full 'Physics and Chemistry of Minerals' _journal_volume 24 _journal_year 1997 _journal_page_first 510 _journal_page_last 519 _publ_section_title ; Structural change associated with the incommensurate-normal phase transition in akermanite, Ca2MgSi2O7, at high pressure Sample: P = 0.80 GPa ; _database_code_amcsd 0008031 _chemical_formula_sum 'Ca2 Mg Si2 O7' _cell_length_a 7.8154 _cell_length_b 7.8154 _cell_length_c 4.9919 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 90 _cell_volume 304.908 _exptl_crystal_density_diffrn 2.969 _symmetry_space_group_name_H-M 'P -4 21 m' loop_ _space_group_symop_operation_xyz 'x,y,z' '1/2-y,1/2-x,z' 'y,-x,-z' '1/2-x,1/2+y,-z' '-x,-y,z' '1/2+y,1/2+x,z' '-y,x,-z' '1/2+x,1/2-y,-z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_U_iso_or_equiv Ca 0.33270 0.16730 0.50630 0.01938 Mg 0.00000 0.00000 0.00000 0.01203 Si 0.13980 0.36020 0.93540 0.01001 O1 0.50000 0.00000 0.18270 0.02280 O2 0.14030 0.35970 0.25610 0.02280 O3 0.08130 0.18520 0.78340 0.02280 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 0.02104 0.02104 0.01603 0.01083 0.00178 0.00178 Mg 0.00835 0.00835 0.01982 0.00000 0.00000 0.00000 Si 0.00990 0.00990 0.01035 0.00155 0.00099 0.00099 O1 0.02971 0.02971 0.00757 -0.01021 0.00000 0.00000 O2 0.02506 0.02506 0.01717 0.00681 -0.00277 -0.00277 O3 0.03528 0.01826 0.01401 -0.00650 0.00731 -0.00198