data_global
_chemical_name_mineral 'Melilite'
loop_
_publ_author_name
'Smith J V'
_journal_name_full 'American Mineralogist'
_journal_volume 38
_journal_year 1953
_journal_page_first 643
_journal_page_last 661
_publ_section_title
;
 Reexamination of the crystal structure of melilite
;
_database_code_amcsd 58
_chemical_formula_sum '(Ca1.7 Na.2 K.1) Si2 Mg.5 Al.4 O7'
_cell_length_a 7.789
_cell_length_b 7.789
_cell_length_c 5.018
_cell_angle_alpha 90.0
_cell_angle_beta 90.0
_cell_angle_gamma 90.0
_cell_volume 304.435
_exptl_crystal_density_diffrn  2.921
_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   0.3355  0.1645  0.5073  0.85
Na   0.3355  0.1645  0.5073  0.1
K   0.3355  0.1645  0.5073  0.05
Si   0.1396  0.3604  0.9412  1.0
Mg   0.0  0.0  0.0  0.5
Al   0.0  0.0  0.0  0.4
O1   0.5  0.0  0.1804  1.0
O2   0.145  0.355  0.2583  1.0
O3   0.082  0.182  0.7909  1.0