The material described by CaAl2Si2O8 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(10), one O(12), one O(14), one O(9), and two equivalent O(2) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(13), one O(15), one O(3), one O(5), one O(7), and two equivalent O(16) atoms. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(4), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(5), one O(6), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. In the third Al site, Al(3) is bonded to one O(11), one O(15), one O(16), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. In the fourth Al site, Al(4) is bonded to one O(10), one O(12), one O(13), and one O(14) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(12), one O(2), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(15), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(3)O4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(13), one O(14), one O(16), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(4)O4 tetrahedra. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Ca(2), one Al(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ca(2), one Al(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Al(2) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(2), one Al(3), and one Si(2) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Al(1) and one Si(4) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(3) atom. In the tenth O site, O(10) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(4), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 120 degrees geometry to one Al(3) and one Si(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(4), and one Si(1) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Ca(2), one Al(4), and one Si(4) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Ca(1), one Al(4), and one Si(4) atom. In the fifteenth O site, O(15) is bonded in a distorted trigonal planar geometry to one Ca(2), one Al(3), and one Si(3) atom. In the sixteenth O site, O(16) is bonded in a 4-coordinate geometry to two equivalent Ca(2), one Al(3), and one Si(4) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaAl2(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.761
_cell_length_b   9.444
_cell_length_c   8.132
_cell_angle_alpha   82.176
_cell_angle_beta   84.944
_cell_angle_gamma   89.714
_symmetry_Int_Tables_number   1
_cell_volume   663.957
_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
  Ca  Ca0  1  0.076  0.002  0.230  1.0
  Ca  Ca1  1  0.418  0.423  0.312  1.0
  Ca  Ca2  1  0.582  0.577  0.688  1.0
  Ca  Ca3  1  0.924  0.998  0.770  1.0
  Al  Al4  1  0.440  0.189  0.001  1.0
  Al  Al5  1  0.067  0.690  0.120  1.0
  Al  Al6  1  0.772  0.453  0.388  1.0
  Al  Al7  1  0.278  0.055  0.522  1.0
  Al  Al8  1  0.722  0.945  0.478  1.0
  Al  Al9  1  0.228  0.547  0.612  1.0
  Al  Al10  1  0.933  0.310  0.880  1.0
  Al  Al11  1  0.560  0.811  0.999  1.0
  Si  Si12  1  0.739  0.054  0.097  1.0
  Si  Si13  1  0.754  0.546  0.023  1.0
  Si  Si14  1  0.054  0.294  0.498  1.0
  Si  Si15  1  0.430  0.794  0.393  1.0
  Si  Si16  1  0.570  0.206  0.607  1.0
  Si  Si17  1  0.946  0.706  0.502  1.0
  Si  Si18  1  0.246  0.454  0.977  1.0
  Si  Si19  1  0.261  0.946  0.903  1.0
  O  O20  1  0.285  0.067  0.024  1.0
  O  O21  1  0.889  0.141  0.999  1.0
  O  O22  1  0.368  0.346  0.068  1.0
  O  O23  1  0.585  0.141  0.128  1.0
  O  O24  1  0.219  0.571  0.106  1.0
  O  O25  1  0.905  0.628  0.054  1.0
  O  O26  1  0.675  0.478  0.207  1.0
  O  O27  1  0.490  0.787  0.204  1.0
  O  O28  1  0.034  0.747  0.317  1.0
  O  O29  1  0.123  0.147  0.433  1.0
  O  O30  1  0.941  0.362  0.366  1.0
  O  O31  1  0.801  0.989  0.273  1.0
  O  O32  1  0.435  0.169  0.494  1.0
  O  O33  1  0.294  0.910  0.409  1.0
  O  O34  1  0.200  0.398  0.510  1.0
  O  O35  1  0.380  0.629  0.474  1.0
  O  O36  1  0.620  0.371  0.526  1.0
  O  O37  1  0.800  0.602  0.490  1.0
  O  O38  1  0.706  0.090  0.591  1.0
  O  O39  1  0.565  0.831  0.506  1.0
  O  O40  1  0.199  0.011  0.727  1.0
  O  O41  1  0.059  0.638  0.634  1.0
  O  O42  1  0.877  0.853  0.567  1.0
  O  O43  1  0.966  0.253  0.683  1.0
  O  O44  1  0.510  0.213  0.796  1.0
  O  O45  1  0.325  0.522  0.793  1.0
  O  O46  1  0.095  0.372  0.946  1.0
  O  O47  1  0.781  0.429  0.894  1.0
  O  O48  1  0.415  0.859  0.872  1.0
  O  O49  1  0.632  0.654  0.932  1.0
  O  O50  1  0.111  0.859  0.001  1.0
  O  O51  1  0.715  0.933  0.976  1.0
[/CIF]
.
The material described by CaAl2Si2O8 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(10), one O(12), one O(14), one O(9), and two equivalent O(2) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(13), one O(15), one O(3), one O(5), one O(7), and two equivalent O(16) atoms. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(4), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(5), one O(6), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. In the third Al site, Al(3) is bonded to one O(11), one O(15), one O(16), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. In the fourth Al site, Al(4) is bonded to one O(10), one O(12), one O(13), and one O(14) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(12), one O(2), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(15), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(3)O4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(13), one O(14), one O(16), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(4)O4 tetrahedra. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Ca(2), one Al(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ca(2), one Al(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Al(2) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(2), one Al(3), and one Si(2) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Al(1) and one Si(4) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(3) atom. In the tenth O site, O(10) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(4), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 120 degrees geometry to one Al(3) and one Si(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(4), and one Si(1) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Ca(2), one Al(4), and one Si(4) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Ca(1), one Al(4), and one Si(4) atom. In the fifteenth O site, O(15) is bonded in a distorted trigonal planar geometry to one Ca(2), one Al(3), and one Si(3) atom. In the sixteenth O site, O(16) is bonded in a 4-coordinate geometry to two equivalent Ca(2), one Al(3), and one Si(4) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaAl2(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.761
_cell_length_b   9.444
_cell_length_c   8.132
_cell_angle_alpha   82.176
_cell_angle_beta   84.944
_cell_angle_gamma   89.714
_symmetry_Int_Tables_number   1
_cell_volume   663.957
_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
  Ca  Ca0  1  0.076  0.002  0.230  1.0
  Ca  Ca1  1  0.418  0.423  0.312  1.0
  Ca  Ca2  1  0.582  0.577  0.688  1.0
  Ca  Ca3  1  0.924  0.998  0.770  1.0
  Al  Al4  1  0.440  0.189  0.001  1.0
  Al  Al5  1  0.067  0.690  0.120  1.0
  Al  Al6  1  0.772  0.453  0.388  1.0
  Al  Al7  1  0.278  0.055  0.522  1.0
  Al  Al8  1  0.722  0.945  0.478  1.0
  Al  Al9  1  0.228  0.547  0.612  1.0
  Al  Al10  1  0.933  0.310  0.880  1.0
  Al  Al11  1  0.560  0.811  0.999  1.0
  Si  Si12  1  0.739  0.054  0.097  1.0
  Si  Si13  1  0.754  0.546  0.023  1.0
  Si  Si14  1  0.054  0.294  0.498  1.0
  Si  Si15  1  0.430  0.794  0.393  1.0
  Si  Si16  1  0.570  0.206  0.607  1.0
  Si  Si17  1  0.946  0.706  0.502  1.0
  Si  Si18  1  0.246  0.454  0.977  1.0
  Si  Si19  1  0.261  0.946  0.903  1.0
  O  O20  1  0.285  0.067  0.024  1.0
  O  O21  1  0.889  0.141  0.999  1.0
  O  O22  1  0.368  0.346  0.068  1.0
  O  O23  1  0.585  0.141  0.128  1.0
  O  O24  1  0.219  0.571  0.106  1.0
  O  O25  1  0.905  0.628  0.054  1.0
  O  O26  1  0.675  0.478  0.207  1.0
  O  O27  1  0.490  0.787  0.204  1.0
  O  O28  1  0.034  0.747  0.317  1.0
  O  O29  1  0.123  0.147  0.433  1.0
  O  O30  1  0.941  0.362  0.366  1.0
  O  O31  1  0.801  0.989  0.273  1.0
  O  O32  1  0.435  0.169  0.494  1.0
  O  O33  1  0.294  0.910  0.409  1.0
  O  O34  1  0.200  0.398  0.510  1.0
  O  O35  1  0.380  0.629  0.474  1.0
  O  O36  1  0.620  0.371  0.526  1.0
  O  O37  1  0.800  0.602  0.490  1.0
  O  O38  1  0.706  0.090  0.591  1.0
  O  O39  1  0.565  0.831  0.506  1.0
  O  O40  1  0.199  0.011  0.727  1.0
  O  O41  1  0.059  0.638  0.634  1.0
  O  O42  1  0.877  0.853  0.567  1.0
  O  O43  1  0.966  0.253  0.683  1.0
  O  O44  1  0.510  0.213  0.796  1.0
  O  O45  1  0.325  0.522  0.793  1.0
  O  O46  1  0.095  0.372  0.946  1.0
  O  O47  1  0.781  0.429  0.894  1.0
  O  O48  1  0.415  0.859  0.872  1.0
  O  O49  1  0.632  0.654  0.932  1.0
  O  O50  1  0.111  0.859  0.001  1.0
  O  O51  1  0.715  0.933  0.976  1.0
[/CIF]
.