data_global _chemical_name_mineral 'Phenakite' loop_ _publ_author_name 'Tsirelson V G' 'Sokolova Y V' 'Urusov V S' _journal_name_full 'Geochemistry International' _journal_volume 24 _journal_year 1987 _journal_page_first 101 _journal_page_last 110 _publ_section_title ; An X-ray diffraction study of the electron-density distribution and electrostatic potential in phenakite Be2SiO4 ; _database_code_amcsd 0020478 _chemical_compound_source 'natural crystal from unreported locality' _chemical_formula_sum 'Be2 Si O4' _cell_length_a 12.485 _cell_length_b 12.485 _cell_length_c 8.264 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 120 _cell_volume 1115.573 _exptl_crystal_density_diffrn 2.950 _symmetry_space_group_name_H-M 'R -3' loop_ _space_group_symop_operation_xyz 'x,y,z' '2/3+x,1/3+y,1/3+z' '1/3+x,2/3+y,2/3+z' 'y,-x+y,-z' '2/3+y,1/3-x+y,1/3-z' '1/3+y,2/3-x+y,2/3-z' '-x+y,-x,z' '2/3-x+y,1/3-x,1/3+z' '1/3-x+y,2/3-x,2/3+z' '-x,-y,-z' '2/3-x,1/3-y,1/3-z' '1/3-x,2/3-y,2/3-z' '-y,x-y,z' '2/3-y,1/3+x-y,1/3+z' '1/3-y,2/3+x-y,2/3+z' 'x-y,x,-z' '2/3+x-y,1/3+x,1/3-z' '1/3+x-y,2/3+x,2/3-z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z Be1 0.98290 0.19422 0.41568 Be2 0.98397 0.19423 0.08424 Si1 0.98394 0.19561 0.75004 O1 0.12104 0.20967 0.74972 O2 0.00007 0.33346 0.75016 O3 0.91341 0.12231 0.91475 O4 0.91235 0.12222 0.58504 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 Be1 0.00468 0.00462 0.00484 0.00148 0.00045 0.00009 Be2 0.00462 0.00557 0.00439 0.00284 0.00000 -0.00072 Si1 0.00237 0.00261 0.00221 0.00124 -0.00005 0.00018 O1 0.00456 0.00669 0.00301 0.00349 -0.00032 -0.00023 O2 0.00503 0.00355 0.00502 0.00243 -0.00063 0.00000 O3 0.00385 0.00326 0.00387 0.00047 0.00009 -0.00009 O4 0.00438 0.00397 0.00311 0.00095 -0.00023 -0.00036