The crystal structure described by CaAl12Si4O27 crystallizes in the trigonal P-3 space group. Ca(1) is bonded to six equivalent O(1) and six equivalent O(4) atoms to form CaO12 cuboctahedra that share corners with six equivalent Al(2)O6 octahedra, corners with six equivalent Si(2)O6 octahedra, edges with six equivalent Al(1)O6 octahedra, and faces with six equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(6), two equivalent O(3), and two equivalent O(4) atoms to form AlO6 octahedra that share  a cornercorner with one Al(1)O6 octahedra,  a cornercorner with one Si(2)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Ca(1)O12 cuboctahedra, and edges with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-57°. In the second Al site, Al(2) is bonded to one O(2), one O(4), one O(5), and three equivalent O(1) atoms to form AlO6 octahedra that share  a cornercorner with one Ca(1)O12 cuboctahedra, corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, edges with two equivalent Si(2)O6 octahedra, edges with three equivalent Al(2)O6 octahedra, and  a faceface with one Ca(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 18-57°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5) and three equivalent O(3) atoms to form SiO4 tetrahedra that share corners with three equivalent Al(2)O6 octahedra and corners with six equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-60°. In the second Si site, Si(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form SiO6 octahedra that share corners with three equivalent Ca(1)O12 cuboctahedra, corners with three equivalent Al(1)O6 octahedra, and edges with six equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are six inequivalent O sites. In the first O site, O(5) is bonded in a distorted tetrahedral geometry to three equivalent Al(2) and one Si(1) atom. In the second O site, O(6) is bonded in an octahedral geometry to six equivalent Al(1) atoms. In the third O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), three equivalent Al(2), and one Si(2) atom. In the fourth O site, O(2) is bonded in a trigonal planar geometry to one Al(1), one Al(2), and one Si(2) atom. In the fifth O site, O(3) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the sixth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Al(2), and two equivalent Al(1) atoms. is represented by the CIF card [CIF]
data_CaAl12Si4O27
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.309
_cell_length_b   7.309
_cell_length_c   8.698
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   402.371
_cell_formula_units_Z   1
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Ca  Ca0  1  0.000  0.000  0.000  1.0
  Al  Al1  1  0.950  0.743  0.353  1.0
  Al  Al2  1  0.453  0.367  0.865  1.0
  Al  Al3  1  0.207  0.950  0.647  1.0
  Al  Al4  1  0.367  0.914  0.135  1.0
  Al  Al5  1  0.547  0.633  0.135  1.0
  Al  Al6  1  0.743  0.793  0.647  1.0
  Al  Al7  1  0.086  0.453  0.135  1.0
  Al  Al8  1  0.914  0.547  0.865  1.0
  Al  Al9  1  0.257  0.207  0.353  1.0
  Al  Al10  1  0.633  0.086  0.865  1.0
  Al  Al11  1  0.793  0.050  0.353  1.0
  Al  Al12  1  0.050  0.257  0.647  1.0
  Si  Si13  1  0.667  0.333  0.554  1.0
  Si  Si14  1  0.333  0.667  0.446  1.0
  Si  Si15  1  0.333  0.667  0.859  1.0
  Si  Si16  1  0.667  0.333  0.141  1.0
  O  O17  1  0.457  0.155  0.001  1.0
  O  O18  1  0.302  0.457  0.999  1.0
  O  O19  1  0.612  0.104  0.238  1.0
  O  O20  1  0.845  0.302  0.001  1.0
  O  O21  1  0.579  0.834  0.492  1.0
  O  O22  1  0.104  0.492  0.762  1.0
  O  O23  1  0.166  0.745  0.492  1.0
  O  O24  1  0.255  0.421  0.492  1.0
  O  O25  1  0.834  0.255  0.508  1.0
  O  O26  1  0.421  0.166  0.508  1.0
  O  O27  1  0.225  0.180  0.759  1.0
  O  O28  1  0.745  0.579  0.508  1.0
  O  O29  1  0.955  0.775  0.759  1.0
  O  O30  1  0.820  0.045  0.759  1.0
  O  O31  1  0.180  0.955  0.241  1.0
  O  O32  1  0.492  0.388  0.238  1.0
  O  O33  1  0.543  0.845  0.999  1.0
  O  O34  1  0.775  0.820  0.241  1.0
  O  O35  1  0.698  0.543  0.001  1.0
  O  O36  1  0.508  0.612  0.762  1.0
  O  O37  1  0.388  0.896  0.762  1.0
  O  O38  1  0.896  0.508  0.238  1.0
  O  O39  1  0.333  0.667  0.249  1.0
  O  O40  1  0.667  0.333  0.751  1.0
  O  O41  1  0.155  0.698  0.999  1.0
  O  O42  1  0.045  0.225  0.241  1.0
  O  O43  1  0.000  0.000  0.500  1.0
[/CIF]
.
The crystal structure described by CaAl12Si4O27 crystallizes in the trigonal P-3 space group. Ca(1) is bonded to six equivalent O(1) and six equivalent O(4) atoms to form CaO12 cuboctahedra that share corners with six equivalent Al(2)O6 octahedra, corners with six equivalent Si(2)O6 octahedra, edges with six equivalent Al(1)O6 octahedra, and faces with six equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(6), two equivalent O(3), and two equivalent O(4) atoms to form AlO6 octahedra that share  a cornercorner with one Al(1)O6 octahedra,  a cornercorner with one Si(2)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Ca(1)O12 cuboctahedra, and edges with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-57°. In the second Al site, Al(2) is bonded to one O(2), one O(4), one O(5), and three equivalent O(1) atoms to form AlO6 octahedra that share  a cornercorner with one Ca(1)O12 cuboctahedra, corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, edges with two equivalent Si(2)O6 octahedra, edges with three equivalent Al(2)O6 octahedra, and  a faceface with one Ca(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 18-57°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5) and three equivalent O(3) atoms to form SiO4 tetrahedra that share corners with three equivalent Al(2)O6 octahedra and corners with six equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-60°. In the second Si site, Si(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form SiO6 octahedra that share corners with three equivalent Ca(1)O12 cuboctahedra, corners with three equivalent Al(1)O6 octahedra, and edges with six equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are six inequivalent O sites. In the first O site, O(5) is bonded in a distorted tetrahedral geometry to three equivalent Al(2) and one Si(1) atom. In the second O site, O(6) is bonded in an octahedral geometry to six equivalent Al(1) atoms. In the third O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), three equivalent Al(2), and one Si(2) atom. In the fourth O site, O(2) is bonded in a trigonal planar geometry to one Al(1), one Al(2), and one Si(2) atom. In the fifth O site, O(3) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the sixth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Al(2), and two equivalent Al(1) atoms. is represented by the CIF card [CIF]
data_CaAl12Si4O27
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.309
_cell_length_b   7.309
_cell_length_c   8.698
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   402.371
_cell_formula_units_Z   1
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Ca  Ca0  1  0.000  0.000  0.000  1.0
  Al  Al1  1  0.950  0.743  0.353  1.0
  Al  Al2  1  0.453  0.367  0.865  1.0
  Al  Al3  1  0.207  0.950  0.647  1.0
  Al  Al4  1  0.367  0.914  0.135  1.0
  Al  Al5  1  0.547  0.633  0.135  1.0
  Al  Al6  1  0.743  0.793  0.647  1.0
  Al  Al7  1  0.086  0.453  0.135  1.0
  Al  Al8  1  0.914  0.547  0.865  1.0
  Al  Al9  1  0.257  0.207  0.353  1.0
  Al  Al10  1  0.633  0.086  0.865  1.0
  Al  Al11  1  0.793  0.050  0.353  1.0
  Al  Al12  1  0.050  0.257  0.647  1.0
  Si  Si13  1  0.667  0.333  0.554  1.0
  Si  Si14  1  0.333  0.667  0.446  1.0
  Si  Si15  1  0.333  0.667  0.859  1.0
  Si  Si16  1  0.667  0.333  0.141  1.0
  O  O17  1  0.457  0.155  0.001  1.0
  O  O18  1  0.302  0.457  0.999  1.0
  O  O19  1  0.612  0.104  0.238  1.0
  O  O20  1  0.845  0.302  0.001  1.0
  O  O21  1  0.579  0.834  0.492  1.0
  O  O22  1  0.104  0.492  0.762  1.0
  O  O23  1  0.166  0.745  0.492  1.0
  O  O24  1  0.255  0.421  0.492  1.0
  O  O25  1  0.834  0.255  0.508  1.0
  O  O26  1  0.421  0.166  0.508  1.0
  O  O27  1  0.225  0.180  0.759  1.0
  O  O28  1  0.745  0.579  0.508  1.0
  O  O29  1  0.955  0.775  0.759  1.0
  O  O30  1  0.820  0.045  0.759  1.0
  O  O31  1  0.180  0.955  0.241  1.0
  O  O32  1  0.492  0.388  0.238  1.0
  O  O33  1  0.543  0.845  0.999  1.0
  O  O34  1  0.775  0.820  0.241  1.0
  O  O35  1  0.698  0.543  0.001  1.0
  O  O36  1  0.508  0.612  0.762  1.0
  O  O37  1  0.388  0.896  0.762  1.0
  O  O38  1  0.896  0.508  0.238  1.0
  O  O39  1  0.333  0.667  0.249  1.0
  O  O40  1  0.667  0.333  0.751  1.0
  O  O41  1  0.155  0.698  0.999  1.0
  O  O42  1  0.045  0.225  0.241  1.0
  O  O43  1  0.000  0.000  0.500  1.0
[/CIF]
.