The material structure described by Ca2AlSi2O7 crystallizes in the tetragonal P-42_1m space group. Ca(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent O(3), and four equivalent O(2) atoms. Al(1) is bonded to four equivalent O(2) atoms to form AlO4 tetrahedra that share corners with four equivalent Si(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Al(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ca(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(1), and one Si(1) atom. In the third O site, O(3) is bonded to three equivalent Ca(1) and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCa3Si tetrahedra. is represented by the CIF file [CIF]
data_Ca2AlSi2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.787
_cell_length_b   7.787
_cell_length_c   5.089
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   308.610
_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  0.164  0.336  0.514  1.0
  Ca  Ca1  1  0.836  0.664  0.514  1.0
  Ca  Ca2  1  0.664  0.164  0.486  1.0
  Ca  Ca3  1  0.336  0.836  0.486  1.0
  Al  Al4  1  0.000  0.000  0.000  1.0
  Al  Al5  1  0.500  0.500  0.000  1.0
  Si  Si6  1  0.642  0.858  0.962  1.0
  Si  Si7  1  0.358  0.142  0.962  1.0
  Si  Si8  1  0.142  0.642  0.038  1.0
  Si  Si9  1  0.858  0.358  0.038  1.0
  O  O10  1  0.000  0.500  0.173  1.0
  O  O11  1  0.500  0.000  0.827  1.0
  O  O12  1  0.083  0.824  0.192  1.0
  O  O13  1  0.917  0.176  0.192  1.0
  O  O14  1  0.176  0.083  0.808  1.0
  O  O15  1  0.417  0.324  0.808  1.0
  O  O16  1  0.824  0.917  0.808  1.0
  O  O17  1  0.583  0.676  0.808  1.0
  O  O18  1  0.324  0.583  0.192  1.0
  O  O19  1  0.676  0.417  0.192  1.0
  O  O20  1  0.636  0.864  0.281  1.0
  O  O21  1  0.364  0.136  0.281  1.0
  O  O22  1  0.136  0.636  0.719  1.0
  O  O23  1  0.864  0.364  0.719  1.0
[/CIF]
.
The material structure described by Ca2AlSi2O7 crystallizes in the tetragonal P-42_1m space group. Ca(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent O(3), and four equivalent O(2) atoms. Al(1) is bonded to four equivalent O(2) atoms to form AlO4 tetrahedra that share corners with four equivalent Si(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Al(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ca(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(1), and one Si(1) atom. In the third O site, O(3) is bonded to three equivalent Ca(1) and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCa3Si tetrahedra. is represented by the CIF file [CIF]
data_Ca2AlSi2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.787
_cell_length_b   7.787
_cell_length_c   5.089
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   308.610
_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  0.164  0.336  0.514  1.0
  Ca  Ca1  1  0.836  0.664  0.514  1.0
  Ca  Ca2  1  0.664  0.164  0.486  1.0
  Ca  Ca3  1  0.336  0.836  0.486  1.0
  Al  Al4  1  0.000  0.000  0.000  1.0
  Al  Al5  1  0.500  0.500  0.000  1.0
  Si  Si6  1  0.642  0.858  0.962  1.0
  Si  Si7  1  0.358  0.142  0.962  1.0
  Si  Si8  1  0.142  0.642  0.038  1.0
  Si  Si9  1  0.858  0.358  0.038  1.0
  O  O10  1  0.000  0.500  0.173  1.0
  O  O11  1  0.500  0.000  0.827  1.0
  O  O12  1  0.083  0.824  0.192  1.0
  O  O13  1  0.917  0.176  0.192  1.0
  O  O14  1  0.176  0.083  0.808  1.0
  O  O15  1  0.417  0.324  0.808  1.0
  O  O16  1  0.824  0.917  0.808  1.0
  O  O17  1  0.583  0.676  0.808  1.0
  O  O18  1  0.324  0.583  0.192  1.0
  O  O19  1  0.676  0.417  0.192  1.0
  O  O20  1  0.636  0.864  0.281  1.0
  O  O21  1  0.364  0.136  0.281  1.0
  O  O22  1  0.136  0.636  0.719  1.0
  O  O23  1  0.864  0.364  0.719  1.0
[/CIF]
.