data_global
_chemical_name_mineral 'Naumannite'
loop_
_publ_author_name
'Wiegers G A'
_journal_name_full 'American Mineralogist'
_journal_volume 56 
_journal_year 1971
_journal_page_first 1882
_journal_page_last 1888
_publ_section_title
;
 The crystal structure of the low-temperature form of silver selenide
;
_database_code_amcsd 0000262
_chemical_formula_sum 'Ag2 Se'
_cell_length_a 4.333
_cell_length_b 7.062
_cell_length_c 7.764
_cell_angle_alpha 90
_cell_angle_beta 90
_cell_angle_gamma 90
_cell_volume 237.576
_exptl_crystal_density_diffrn      8.239
_symmetry_space_group_name_H-M 'P 21 21 21'
loop_
_space_group_symop_operation_xyz
  'x,y,z'
  '1/2-x,1/2+y,1/2-z'
  '1/2+x,-y,-z'
  '-x,1/2-y,1/2+z'
loop_
_atom_site_label
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
Ag1   0.10700   0.36900   0.45600   0.00950
Ag2   0.72800   0.02900   0.36100   0.00950
Se   0.35800   0.23500   0.14900   0.00950