The material structure described by Ca2Al4Si4O17 crystallizes in the monoclinic C2/c space group. Ca(1) is bonded in a 6-coordinate geometry to one O(3), one O(5), one O(6), one O(9), and two equivalent O(7) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(4), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three 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(3), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(4), 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 and corners with three equivalent Al(2)O4 tetrahedra. There are nine inequivalent O sites. In the first O site, O(7) is bonded to two equivalent Ca(1), one Al(2), and one Si(2) atom to form distorted edge-sharing OCa2AlSi trigonal pyramids. In the second O site, O(8) is bonded in a bent 120 degrees geometry to two equivalent Si(1) atoms. In the third O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one Al(1) atom. In the fourth O site, O(1) is bonded in a linear geometry to one Al(1) and one Si(1) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to 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(2), and one Si(2) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(1) atom. In the eighth O site, O(4) is bonded in a linear geometry to one Al(1) and one Si(2) atom. In the ninth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Al(2), and one Si(2) atom. is represented by the CIF file [CIF]
data_Ca2Al4Si4O17
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.584
_cell_length_b   9.402
_cell_length_c   11.525
_cell_angle_alpha   114.073
_cell_angle_beta   99.256
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   835.922
_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  0.558  0.483  0.331  1.0
  Ca  Ca1  1  0.942  0.152  0.669  1.0
  Ca  Ca2  1  0.442  0.517  0.669  1.0
  Ca  Ca3  1  0.058  0.848  0.331  1.0
  Al  Al4  1  0.145  0.782  0.811  1.0
  Al  Al5  1  0.355  0.971  0.189  1.0
  Al  Al6  1  0.855  0.218  0.189  1.0
  Al  Al7  1  0.645  0.029  0.811  1.0
  Al  Al8  1  0.789  0.485  0.593  1.0
  Al  Al9  1  0.711  0.892  0.407  1.0
  Al  Al10  1  0.211  0.515  0.407  1.0
  Al  Al11  1  0.289  0.108  0.593  1.0
  Si  Si12  1  0.809  0.742  0.875  1.0
  Si  Si13  1  0.691  0.867  0.125  1.0
  Si  Si14  1  0.191  0.258  0.125  1.0
  Si  Si15  1  0.309  0.133  0.875  1.0
  Si  Si16  1  0.950  0.707  0.515  1.0
  Si  Si17  1  0.550  0.191  0.485  1.0
  Si  Si18  1  0.050  0.293  0.485  1.0
  Si  Si19  1  0.450  0.809  0.515  1.0
  O  O20  1  0.739  0.896  0.862  1.0
  O  O21  1  0.761  0.034  0.138  1.0
  O  O22  1  0.261  0.104  0.138  1.0
  O  O23  1  0.239  0.966  0.862  1.0
  O  O24  1  0.999  0.745  0.886  1.0
  O  O25  1  0.501  0.859  0.114  1.0
  O  O26  1  0.001  0.255  0.114  1.0
  O  O27  1  0.499  0.141  0.886  1.0
  O  O28  1  0.725  0.585  0.742  1.0
  O  O29  1  0.775  0.843  0.258  1.0
  O  O30  1  0.275  0.415  0.258  1.0
  O  O31  1  0.225  0.157  0.742  1.0
  O  O32  1  0.557  0.913  0.651  1.0
  O  O33  1  0.943  0.262  0.349  1.0
  O  O34  1  0.443  0.087  0.349  1.0
  O  O35  1  0.057  0.738  0.651  1.0
  O  O36  1  0.949  0.370  0.604  1.0
  O  O37  1  0.551  0.765  0.396  1.0
  O  O38  1  0.051  0.630  0.396  1.0
  O  O39  1  0.449  0.235  0.604  1.0
  O  O40  1  0.797  0.587  0.494  1.0
  O  O41  1  0.703  0.093  0.506  1.0
  O  O42  1  0.203  0.413  0.506  1.0
  O  O43  1  0.297  0.907  0.494  1.0
  O  O44  1  0.890  0.868  0.502  1.0
  O  O45  1  0.610  0.366  0.498  1.0
  O  O46  1  0.110  0.132  0.498  1.0
  O  O47  1  0.390  0.634  0.502  1.0
  O  O48  1  0.750  0.729  0.000  1.0
  O  O49  1  0.250  0.271  0.000  1.0
  O  O50  1  0.689  0.329  0.181  1.0
  O  O51  1  0.811  0.148  0.819  1.0
  O  O52  1  0.311  0.671  0.819  1.0
  O  O53  1  0.189  0.852  0.181  1.0
[/CIF]
.
The material structure described by Ca2Al4Si4O17 crystallizes in the monoclinic C2/c space group. Ca(1) is bonded in a 6-coordinate geometry to one O(3), one O(5), one O(6), one O(9), and two equivalent O(7) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(4), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three 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(3), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(4), 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 and corners with three equivalent Al(2)O4 tetrahedra. There are nine inequivalent O sites. In the first O site, O(7) is bonded to two equivalent Ca(1), one Al(2), and one Si(2) atom to form distorted edge-sharing OCa2AlSi trigonal pyramids. In the second O site, O(8) is bonded in a bent 120 degrees geometry to two equivalent Si(1) atoms. In the third O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one Al(1) atom. In the fourth O site, O(1) is bonded in a linear geometry to one Al(1) and one Si(1) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to 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(2), and one Si(2) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(1) atom. In the eighth O site, O(4) is bonded in a linear geometry to one Al(1) and one Si(2) atom. In the ninth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Al(2), and one Si(2) atom. is represented by the CIF file [CIF]
data_Ca2Al4Si4O17
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.584
_cell_length_b   9.402
_cell_length_c   11.525
_cell_angle_alpha   114.073
_cell_angle_beta   99.256
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   835.922
_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  0.558  0.483  0.331  1.0
  Ca  Ca1  1  0.942  0.152  0.669  1.0
  Ca  Ca2  1  0.442  0.517  0.669  1.0
  Ca  Ca3  1  0.058  0.848  0.331  1.0
  Al  Al4  1  0.145  0.782  0.811  1.0
  Al  Al5  1  0.355  0.971  0.189  1.0
  Al  Al6  1  0.855  0.218  0.189  1.0
  Al  Al7  1  0.645  0.029  0.811  1.0
  Al  Al8  1  0.789  0.485  0.593  1.0
  Al  Al9  1  0.711  0.892  0.407  1.0
  Al  Al10  1  0.211  0.515  0.407  1.0
  Al  Al11  1  0.289  0.108  0.593  1.0
  Si  Si12  1  0.809  0.742  0.875  1.0
  Si  Si13  1  0.691  0.867  0.125  1.0
  Si  Si14  1  0.191  0.258  0.125  1.0
  Si  Si15  1  0.309  0.133  0.875  1.0
  Si  Si16  1  0.950  0.707  0.515  1.0
  Si  Si17  1  0.550  0.191  0.485  1.0
  Si  Si18  1  0.050  0.293  0.485  1.0
  Si  Si19  1  0.450  0.809  0.515  1.0
  O  O20  1  0.739  0.896  0.862  1.0
  O  O21  1  0.761  0.034  0.138  1.0
  O  O22  1  0.261  0.104  0.138  1.0
  O  O23  1  0.239  0.966  0.862  1.0
  O  O24  1  0.999  0.745  0.886  1.0
  O  O25  1  0.501  0.859  0.114  1.0
  O  O26  1  0.001  0.255  0.114  1.0
  O  O27  1  0.499  0.141  0.886  1.0
  O  O28  1  0.725  0.585  0.742  1.0
  O  O29  1  0.775  0.843  0.258  1.0
  O  O30  1  0.275  0.415  0.258  1.0
  O  O31  1  0.225  0.157  0.742  1.0
  O  O32  1  0.557  0.913  0.651  1.0
  O  O33  1  0.943  0.262  0.349  1.0
  O  O34  1  0.443  0.087  0.349  1.0
  O  O35  1  0.057  0.738  0.651  1.0
  O  O36  1  0.949  0.370  0.604  1.0
  O  O37  1  0.551  0.765  0.396  1.0
  O  O38  1  0.051  0.630  0.396  1.0
  O  O39  1  0.449  0.235  0.604  1.0
  O  O40  1  0.797  0.587  0.494  1.0
  O  O41  1  0.703  0.093  0.506  1.0
  O  O42  1  0.203  0.413  0.506  1.0
  O  O43  1  0.297  0.907  0.494  1.0
  O  O44  1  0.890  0.868  0.502  1.0
  O  O45  1  0.610  0.366  0.498  1.0
  O  O46  1  0.110  0.132  0.498  1.0
  O  O47  1  0.390  0.634  0.502  1.0
  O  O48  1  0.750  0.729  0.000  1.0
  O  O49  1  0.250  0.271  0.000  1.0
  O  O50  1  0.689  0.329  0.181  1.0
  O  O51  1  0.811  0.148  0.819  1.0
  O  O52  1  0.311  0.671  0.819  1.0
  O  O53  1  0.189  0.852  0.181  1.0
[/CIF]
.