data_global _chemical_name_mineral 'Akermanite' loop_ _publ_author_name 'Warren B' _journal_name_full 'Zeitschrift fur Kristallographie' _journal_volume 74 _journal_year 1930 _journal_page_first 131 _journal_page_last 138 _publ_section_title ; The structure of melitite (Ca,Na)2(Mg,Al)(Si,Al)2O7 _cod_database_code 1010215 ; _database_code_amcsd 0017151 _chemical_formula_sum 'Ca2 Si2 Mg O7' _cell_length_a 7.73 _cell_length_b 7.73 _cell_length_c 5.01 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 90 _cell_volume 299.362 _exptl_crystal_density_diffrn 3.024 _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 Ca 0.33000 0.17000 -0.49000 Si 0.14000 0.36000 -0.05000 Mg 0.00000 0.00000 0.00000 O1 0.50000 0.00000 0.19000 O2 0.14000 0.36000 0.26000 O3 0.08000 0.18000 -0.19000