The crystal structure described by BaAl2Si2O8 crystallizes in the monoclinic P2_1/c space group. Ba(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with three equivalent Si(1)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with three equivalent Al(2)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with three equivalent Al(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Al(1), and one Si(2) atom. In the second O site, O(5) is bonded in a 2-coordinate geometry to one Ba(1), one Al(2), and one Si(1) atom. In the third O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Si(2) atom. In the fourth O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(2), and one Si(1) atom. In the fifth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Si(2) atom. In the sixth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one Si(1) atom. In the seventh O site, O(2) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(2) atom. In the eighth O site, O(3) is bonded in a 3-coordinate geometry to one Ba(1), one Al(2), and one Si(1) atom. is represented by the CIF card [CIF]
data_BaAl2(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.581
_cell_length_b   9.070
_cell_length_c   9.599
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.191
_symmetry_Int_Tables_number   1
_cell_volume   747.102
_cell_formula_units_Z   4
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
  Ba  Ba0  1  0.251  0.398  0.089  1.0
  Ba  Ba1  1  0.749  0.102  0.589  1.0
  Ba  Ba2  1  0.749  0.602  0.911  1.0
  Ba  Ba3  1  0.251  0.898  0.411  1.0
  Al  Al4  1  0.931  0.725  0.578  1.0
  Al  Al5  1  0.069  0.775  0.078  1.0
  Al  Al6  1  0.069  0.275  0.422  1.0
  Al  Al7  1  0.931  0.225  0.922  1.0
  Al  Al8  1  0.572  0.564  0.307  1.0
  Al  Al9  1  0.428  0.936  0.807  1.0
  Al  Al10  1  0.428  0.436  0.693  1.0
  Al  Al11  1  0.572  0.064  0.193  1.0
  Si  Si12  1  0.563  0.732  0.583  1.0
  Si  Si13  1  0.437  0.768  0.083  1.0
  Si  Si14  1  0.437  0.268  0.417  1.0
  Si  Si15  1  0.563  0.232  0.917  1.0
  Si  Si16  1  0.941  0.569  0.301  1.0
  Si  Si17  1  0.059  0.931  0.801  1.0
  Si  Si18  1  0.059  0.431  0.699  1.0
  Si  Si19  1  0.941  0.069  0.199  1.0
  O  O20  1  0.741  0.793  0.588  1.0
  O  O21  1  0.259  0.707  0.088  1.0
  O  O22  1  0.259  0.207  0.412  1.0
  O  O23  1  0.741  0.293  0.912  1.0
  O  O24  1  0.765  0.521  0.335  1.0
  O  O25  1  0.235  0.979  0.835  1.0
  O  O26  1  0.235  0.479  0.665  1.0
  O  O27  1  0.765  0.021  0.165  1.0
  O  O28  1  0.450  0.409  0.315  1.0
  O  O29  1  0.550  0.091  0.815  1.0
  O  O30  1  0.550  0.591  0.685  1.0
  O  O31  1  0.450  0.909  0.185  1.0
  O  O32  1  0.059  0.430  0.316  1.0
  O  O33  1  0.941  0.070  0.816  1.0
  O  O34  1  0.941  0.570  0.684  1.0
  O  O35  1  0.059  0.930  0.184  1.0
  O  O36  1  0.545  0.631  0.137  1.0
  O  O37  1  0.455  0.869  0.637  1.0
  O  O38  1  0.455  0.369  0.863  1.0
  O  O39  1  0.545  0.131  0.363  1.0
  O  O40  1  1.000  0.196  0.090  1.0
  O  O41  1  0.000  0.304  0.590  1.0
  O  O42  1  0.000  0.804  0.910  1.0
  O  O43  1  1.000  0.696  0.410  1.0
  O  O44  1  0.504  0.194  0.073  1.0
  O  O45  1  0.496  0.306  0.573  1.0
  O  O46  1  0.496  0.806  0.927  1.0
  O  O47  1  0.504  0.694  0.427  1.0
  O  O48  1  0.956  0.128  0.359  1.0
  O  O49  1  0.044  0.372  0.859  1.0
  O  O50  1  0.044  0.872  0.641  1.0
  O  O51  1  0.956  0.628  0.141  1.0
[/CIF]
.
The crystal structure described by BaAl2Si2O8 crystallizes in the monoclinic P2_1/c space group. Ba(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with three equivalent Si(1)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with three equivalent Al(2)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with three equivalent Al(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Al(1), and one Si(2) atom. In the second O site, O(5) is bonded in a 2-coordinate geometry to one Ba(1), one Al(2), and one Si(1) atom. In the third O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Si(2) atom. In the fourth O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(2), and one Si(1) atom. In the fifth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Si(2) atom. In the sixth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one Si(1) atom. In the seventh O site, O(2) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(2) atom. In the eighth O site, O(3) is bonded in a 3-coordinate geometry to one Ba(1), one Al(2), and one Si(1) atom. is represented by the CIF card [CIF]
data_BaAl2(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.581
_cell_length_b   9.070
_cell_length_c   9.599
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.191
_symmetry_Int_Tables_number   1
_cell_volume   747.102
_cell_formula_units_Z   4
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
  Ba  Ba0  1  0.251  0.398  0.089  1.0
  Ba  Ba1  1  0.749  0.102  0.589  1.0
  Ba  Ba2  1  0.749  0.602  0.911  1.0
  Ba  Ba3  1  0.251  0.898  0.411  1.0
  Al  Al4  1  0.931  0.725  0.578  1.0
  Al  Al5  1  0.069  0.775  0.078  1.0
  Al  Al6  1  0.069  0.275  0.422  1.0
  Al  Al7  1  0.931  0.225  0.922  1.0
  Al  Al8  1  0.572  0.564  0.307  1.0
  Al  Al9  1  0.428  0.936  0.807  1.0
  Al  Al10  1  0.428  0.436  0.693  1.0
  Al  Al11  1  0.572  0.064  0.193  1.0
  Si  Si12  1  0.563  0.732  0.583  1.0
  Si  Si13  1  0.437  0.768  0.083  1.0
  Si  Si14  1  0.437  0.268  0.417  1.0
  Si  Si15  1  0.563  0.232  0.917  1.0
  Si  Si16  1  0.941  0.569  0.301  1.0
  Si  Si17  1  0.059  0.931  0.801  1.0
  Si  Si18  1  0.059  0.431  0.699  1.0
  Si  Si19  1  0.941  0.069  0.199  1.0
  O  O20  1  0.741  0.793  0.588  1.0
  O  O21  1  0.259  0.707  0.088  1.0
  O  O22  1  0.259  0.207  0.412  1.0
  O  O23  1  0.741  0.293  0.912  1.0
  O  O24  1  0.765  0.521  0.335  1.0
  O  O25  1  0.235  0.979  0.835  1.0
  O  O26  1  0.235  0.479  0.665  1.0
  O  O27  1  0.765  0.021  0.165  1.0
  O  O28  1  0.450  0.409  0.315  1.0
  O  O29  1  0.550  0.091  0.815  1.0
  O  O30  1  0.550  0.591  0.685  1.0
  O  O31  1  0.450  0.909  0.185  1.0
  O  O32  1  0.059  0.430  0.316  1.0
  O  O33  1  0.941  0.070  0.816  1.0
  O  O34  1  0.941  0.570  0.684  1.0
  O  O35  1  0.059  0.930  0.184  1.0
  O  O36  1  0.545  0.631  0.137  1.0
  O  O37  1  0.455  0.869  0.637  1.0
  O  O38  1  0.455  0.369  0.863  1.0
  O  O39  1  0.545  0.131  0.363  1.0
  O  O40  1  1.000  0.196  0.090  1.0
  O  O41  1  0.000  0.304  0.590  1.0
  O  O42  1  0.000  0.804  0.910  1.0
  O  O43  1  1.000  0.696  0.410  1.0
  O  O44  1  0.504  0.194  0.073  1.0
  O  O45  1  0.496  0.306  0.573  1.0
  O  O46  1  0.496  0.806  0.927  1.0
  O  O47  1  0.504  0.694  0.427  1.0
  O  O48  1  0.956  0.128  0.359  1.0
  O  O49  1  0.044  0.372  0.859  1.0
  O  O50  1  0.044  0.872  0.641  1.0
  O  O51  1  0.956  0.628  0.141  1.0
[/CIF]
.