The crystal structure described by Ca2Al2SiO8 crystallizes in the tetragonal I-42m space group. Ca(1) is bonded to one O(2), two equivalent O(3), and three equivalent O(1) atoms to form distorted CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Al(1)O4 tetrahedra, and edges with three equivalent Ca(1)O6 octahedra. Al(1) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form AlO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra, corners with two equivalent Al(1)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 67-69°. Si(1) is bonded to four equivalent O(3) atoms to form SiO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra and corners with four equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to three equivalent Ca(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Al(1) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Al2SiO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.719
_cell_length_b   7.719
_cell_length_c   7.719
_cell_angle_alpha   109.089
_cell_angle_beta   109.089
_cell_angle_gamma   110.238
_symmetry_Int_Tables_number   1
_cell_volume   354.059
_cell_formula_units_Z   2
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  0.695  0.695  0.695  1.0
  Ca  Ca1  1  1.000  1.000  0.305  1.0
  Ca  Ca2  1  0.305  0.000  0.000  1.0
  Ca  Ca3  1  0.000  0.305  0.000  1.0
  Al  Al4  1  0.752  0.500  0.252  1.0
  Al  Al5  1  0.500  0.248  0.748  1.0
  Al  Al6  1  0.500  0.752  0.252  1.0
  Al  Al7  1  0.248  0.500  0.748  1.0
  Si  Si8  1  0.250  0.750  0.500  1.0
  Si  Si9  1  0.750  0.250  0.500  1.0
  O  O10  1  0.203  0.203  0.195  1.0
  O  O11  1  0.007  0.007  0.805  1.0
  O  O12  1  0.797  0.993  0.000  1.0
  O  O13  1  0.993  0.797  0.000  1.0
  O  O14  1  0.429  0.429  0.706  1.0
  O  O15  1  0.431  0.724  0.445  1.0
  O  O16  1  0.724  0.431  0.445  1.0
  O  O17  1  0.723  0.723  0.294  1.0
  O  O18  1  0.279  0.986  0.555  1.0
  O  O19  1  0.986  0.279  0.555  1.0
  O  O20  1  0.571  0.277  0.000  1.0
  O  O21  1  0.569  0.014  0.293  1.0
  O  O22  1  0.276  0.721  0.707  1.0
  O  O23  1  0.277  0.571  0.000  1.0
  O  O24  1  0.721  0.276  0.707  1.0
  O  O25  1  0.014  0.569  0.293  1.0
[/CIF]
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The crystal structure described by Ca2Al2SiO8 crystallizes in the tetragonal I-42m space group. Ca(1) is bonded to one O(2), two equivalent O(3), and three equivalent O(1) atoms to form distorted CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Al(1)O4 tetrahedra, and edges with three equivalent Ca(1)O6 octahedra. Al(1) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form AlO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra, corners with two equivalent Al(1)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 67-69°. Si(1) is bonded to four equivalent O(3) atoms to form SiO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra and corners with four equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to three equivalent Ca(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Al(1) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Al2SiO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.719
_cell_length_b   7.719
_cell_length_c   7.719
_cell_angle_alpha   109.089
_cell_angle_beta   109.089
_cell_angle_gamma   110.238
_symmetry_Int_Tables_number   1
_cell_volume   354.059
_cell_formula_units_Z   2
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  0.695  0.695  0.695  1.0
  Ca  Ca1  1  1.000  1.000  0.305  1.0
  Ca  Ca2  1  0.305  0.000  0.000  1.0
  Ca  Ca3  1  0.000  0.305  0.000  1.0
  Al  Al4  1  0.752  0.500  0.252  1.0
  Al  Al5  1  0.500  0.248  0.748  1.0
  Al  Al6  1  0.500  0.752  0.252  1.0
  Al  Al7  1  0.248  0.500  0.748  1.0
  Si  Si8  1  0.250  0.750  0.500  1.0
  Si  Si9  1  0.750  0.250  0.500  1.0
  O  O10  1  0.203  0.203  0.195  1.0
  O  O11  1  0.007  0.007  0.805  1.0
  O  O12  1  0.797  0.993  0.000  1.0
  O  O13  1  0.993  0.797  0.000  1.0
  O  O14  1  0.429  0.429  0.706  1.0
  O  O15  1  0.431  0.724  0.445  1.0
  O  O16  1  0.724  0.431  0.445  1.0
  O  O17  1  0.723  0.723  0.294  1.0
  O  O18  1  0.279  0.986  0.555  1.0
  O  O19  1  0.986  0.279  0.555  1.0
  O  O20  1  0.571  0.277  0.000  1.0
  O  O21  1  0.569  0.014  0.293  1.0
  O  O22  1  0.276  0.721  0.707  1.0
  O  O23  1  0.277  0.571  0.000  1.0
  O  O24  1  0.721  0.276  0.707  1.0
  O  O25  1  0.014  0.569  0.293  1.0
[/CIF]
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