data_global _chemical_name_mineral 'Akermanite' loop_ _publ_author_name 'Kusaka K' 'Ohmasa M' 'Hagiya K' 'Iishi K' 'Haga N' _journal_name_full 'Mineralogical Journal' _journal_volume 20 _journal_year 1998 _journal_page_first 47 _journal_page_last 58 _publ_section_title ; On variety of the Ca coordination in the incommensurate structure of synthetic iron-bearing akermanite, Ca2(Mg0.55,Fe0.45)Si2O7 Note: Sample is synthetic, this is the structure obtained by refining the incommensurate structure ; _database_code_amcsd 0014432 _chemical_formula_sum 'Ca2 (Mg.554 Fe.446) Si2 O7' _cell_length_a 7.8679 _cell_length_b 7.8679 _cell_length_c 5.0144 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 90 _cell_volume 310.411 _exptl_crystal_density_diffrn 3.067 _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_occupancy Ca 0.33070 0.16930 0.50610 1.00000 Mg 0.00000 0.00000 0.00000 0.55400 Fe 0.00000 0.00000 0.00000 0.44600 Si 0.13840 0.36160 0.93830 1.00000 O1 0.00000 0.50000 0.82500 1.00000 O2 0.13900 0.36100 0.25700 1.00000 O3 0.07950 0.18980 0.78910 1.00000 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 0.02007 0.02007 0.00892 0.01035 0.00160 -0.00160 Mg 0.00972 0.00972 0.01210 0.00000 0.00000 0.00000 Fe 0.00972 0.00972 0.01210 0.00000 0.00000 0.00000 Si 0.00847 0.00847 0.00624 0.00220 0.00040 -0.00040 O1 0.04171 0.04171 0.00637 0.03262 0.00000 0.00000 O2 0.03073 0.03073 0.00522 0.01662 -0.00100 0.00100 O3 0.03826 0.01192 0.01261 -0.00909 0.00660 -0.00160