The compound described by Ca2Al2(SiO4)3 crystallizes in the monoclinic P2/c space group. Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(4), one O(5), one O(6), and two equivalent O(3) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to two equivalent O(2) and two equivalent O(4) atoms to form AlO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra,  a cornercorner with one Al(2)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-51°. In the second Si site, Si(2) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Al(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to two equivalent Ca(1) and one Al(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. In the sixth O site, O(6) 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_Ca2Al2(SiO4)3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.705
_cell_length_b   5.517
_cell_length_c   19.389
_cell_angle_alpha   74.591
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   485.144
_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  0.009  0.404  0.601  1.0
  Ca  Ca1  1  0.009  0.596  0.899  1.0
  Ca  Ca2  1  0.991  0.596  0.399  1.0
  Ca  Ca3  1  0.991  0.404  0.101  1.0
  Al  Al4  1  0.000  0.000  0.500  1.0
  Al  Al5  1  0.000  0.000  0.000  1.0
  Al  Al6  1  0.194  0.500  0.750  1.0
  Al  Al7  1  0.806  0.500  0.250  1.0
  Si  Si8  1  0.499  0.874  0.619  1.0
  Si  Si9  1  0.499  0.126  0.881  1.0
  Si  Si10  1  0.501  0.126  0.381  1.0
  Si  Si11  1  0.501  0.874  0.119  1.0
  Si  Si12  1  0.808  0.000  0.750  1.0
  Si  Si13  1  0.192  0.000  0.250  1.0
  O  O14  1  0.622  0.030  0.677  1.0
  O  O15  1  0.362  0.608  0.667  1.0
  O  O16  1  0.622  0.970  0.823  1.0
  O  O17  1  0.362  0.392  0.833  1.0
  O  O18  1  0.378  0.970  0.323  1.0
  O  O19  1  0.638  0.392  0.333  1.0
  O  O20  1  0.378  0.030  0.177  1.0
  O  O21  1  0.638  0.608  0.167  1.0
  O  O22  1  0.826  0.309  0.501  1.0
  O  O23  1  0.174  0.691  0.499  1.0
  O  O24  1  0.826  0.691  0.999  1.0
  O  O25  1  0.174  0.309  0.001  1.0
  O  O26  1  0.994  0.257  0.731  1.0
  O  O27  1  0.994  0.743  0.769  1.0
  O  O28  1  0.006  0.743  0.269  1.0
  O  O29  1  0.006  0.257  0.231  1.0
  O  O30  1  0.256  0.059  0.573  1.0
  O  O31  1  0.765  0.804  0.575  1.0
  O  O32  1  0.256  0.941  0.927  1.0
  O  O33  1  0.765  0.196  0.925  1.0
  O  O34  1  0.744  0.941  0.427  1.0
  O  O35  1  0.235  0.196  0.425  1.0
  O  O36  1  0.744  0.059  0.073  1.0
  O  O37  1  0.235  0.804  0.075  1.0
[/CIF]
.
The compound described by Ca2Al2(SiO4)3 crystallizes in the monoclinic P2/c space group. Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(4), one O(5), one O(6), and two equivalent O(3) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to two equivalent O(2) and two equivalent O(4) atoms to form AlO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra,  a cornercorner with one Al(2)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-51°. In the second Si site, Si(2) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Al(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to two equivalent Ca(1) and one Al(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. In the sixth O site, O(6) 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_Ca2Al2(SiO4)3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.705
_cell_length_b   5.517
_cell_length_c   19.389
_cell_angle_alpha   74.591
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   485.144
_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  0.009  0.404  0.601  1.0
  Ca  Ca1  1  0.009  0.596  0.899  1.0
  Ca  Ca2  1  0.991  0.596  0.399  1.0
  Ca  Ca3  1  0.991  0.404  0.101  1.0
  Al  Al4  1  0.000  0.000  0.500  1.0
  Al  Al5  1  0.000  0.000  0.000  1.0
  Al  Al6  1  0.194  0.500  0.750  1.0
  Al  Al7  1  0.806  0.500  0.250  1.0
  Si  Si8  1  0.499  0.874  0.619  1.0
  Si  Si9  1  0.499  0.126  0.881  1.0
  Si  Si10  1  0.501  0.126  0.381  1.0
  Si  Si11  1  0.501  0.874  0.119  1.0
  Si  Si12  1  0.808  0.000  0.750  1.0
  Si  Si13  1  0.192  0.000  0.250  1.0
  O  O14  1  0.622  0.030  0.677  1.0
  O  O15  1  0.362  0.608  0.667  1.0
  O  O16  1  0.622  0.970  0.823  1.0
  O  O17  1  0.362  0.392  0.833  1.0
  O  O18  1  0.378  0.970  0.323  1.0
  O  O19  1  0.638  0.392  0.333  1.0
  O  O20  1  0.378  0.030  0.177  1.0
  O  O21  1  0.638  0.608  0.167  1.0
  O  O22  1  0.826  0.309  0.501  1.0
  O  O23  1  0.174  0.691  0.499  1.0
  O  O24  1  0.826  0.691  0.999  1.0
  O  O25  1  0.174  0.309  0.001  1.0
  O  O26  1  0.994  0.257  0.731  1.0
  O  O27  1  0.994  0.743  0.769  1.0
  O  O28  1  0.006  0.743  0.269  1.0
  O  O29  1  0.006  0.257  0.231  1.0
  O  O30  1  0.256  0.059  0.573  1.0
  O  O31  1  0.765  0.804  0.575  1.0
  O  O32  1  0.256  0.941  0.927  1.0
  O  O33  1  0.765  0.196  0.925  1.0
  O  O34  1  0.744  0.941  0.427  1.0
  O  O35  1  0.235  0.196  0.425  1.0
  O  O36  1  0.744  0.059  0.073  1.0
  O  O37  1  0.235  0.804  0.075  1.0
[/CIF]
.