The structure described by Ca6Si2O13 crystallizes in the trigonal P-3 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms to form CaO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles are 61°. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(5), two equivalent O(1), and two equivalent O(3) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with six equivalent Ca(1)O6 octahedra and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-53°. In the second Si site, Si(2) is bonded to one O(5) and three equivalent O(1) atoms to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. There are five inequivalent O sites. In the first O site, O(5) is bonded in a linear geometry to three equivalent Ca(2), one Si(1), and one Si(2) atom. In the second O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), two equivalent Ca(2), and one Si(2) atom. In the third O site, O(2) is bonded to one Ca(2), two equivalent Ca(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCa3Si trigonal pyramids. In the fourth O site, O(3) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ca(2) atoms. In the fifth O site, O(4) is bonded in a trigonal planar geometry to one Ca(2) and two equivalent Ca(1) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca6Si2O13
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.181
_cell_length_b   10.181
_cell_length_c   7.580
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   680.400
_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  0.666  0.621  0.622  1.0
  Ca  Ca1  1  0.955  0.334  0.622  1.0
  Ca  Ca2  1  0.379  0.045  0.622  1.0
  Ca  Ca3  1  0.334  0.379  0.378  1.0
  Ca  Ca4  1  0.045  0.666  0.378  1.0
  Ca  Ca5  1  0.621  0.955  0.378  1.0
  Ca  Ca6  1  0.335  0.382  0.870  1.0
  Ca  Ca7  1  0.047  0.665  0.870  1.0
  Ca  Ca8  1  0.618  0.953  0.870  1.0
  Ca  Ca9  1  0.382  0.047  0.130  1.0
  Ca  Ca10  1  0.665  0.618  0.130  1.0
  Ca  Ca11  1  0.953  0.335  0.130  1.0
  Si  Si12  1  0.333  0.667  0.656  1.0
  Si  Si13  1  0.667  0.333  0.344  1.0
  Si  Si14  1  0.333  0.667  0.094  1.0
  Si  Si15  1  0.667  0.333  0.906  1.0
  O  O16  1  0.412  0.565  0.147  1.0
  O  O17  1  0.153  0.588  0.147  1.0
  O  O18  1  0.435  0.847  0.147  1.0
  O  O19  1  0.586  0.433  0.397  1.0
  O  O20  1  0.847  0.414  0.397  1.0
  O  O21  1  0.567  0.153  0.397  1.0
  O  O22  1  0.414  0.567  0.603  1.0
  O  O23  1  0.153  0.586  0.603  1.0
  O  O24  1  0.433  0.847  0.603  1.0
  O  O25  1  0.236  0.917  0.881  1.0
  O  O26  1  0.682  0.764  0.881  1.0
  O  O27  1  0.083  0.318  0.881  1.0
  O  O28  1  0.229  0.928  0.369  1.0
  O  O29  1  0.699  0.771  0.369  1.0
  O  O30  1  0.072  0.301  0.369  1.0
  O  O31  1  0.318  0.236  0.119  1.0
  O  O32  1  0.917  0.682  0.119  1.0
  O  O33  1  0.764  0.083  0.119  1.0
  O  O34  1  0.333  0.667  0.875  1.0
  O  O35  1  0.667  0.333  0.125  1.0
  O  O36  1  0.301  0.229  0.631  1.0
  O  O37  1  0.928  0.699  0.631  1.0
  O  O38  1  0.771  0.072  0.631  1.0
  O  O39  1  0.588  0.435  0.853  1.0
  O  O40  1  0.847  0.412  0.853  1.0
  O  O41  1  0.565  0.153  0.853  1.0
[/CIF]
.
The structure described by Ca6Si2O13 crystallizes in the trigonal P-3 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms to form CaO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles are 61°. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(5), two equivalent O(1), and two equivalent O(3) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with six equivalent Ca(1)O6 octahedra and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-53°. In the second Si site, Si(2) is bonded to one O(5) and three equivalent O(1) atoms to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. There are five inequivalent O sites. In the first O site, O(5) is bonded in a linear geometry to three equivalent Ca(2), one Si(1), and one Si(2) atom. In the second O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), two equivalent Ca(2), and one Si(2) atom. In the third O site, O(2) is bonded to one Ca(2), two equivalent Ca(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCa3Si trigonal pyramids. In the fourth O site, O(3) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ca(2) atoms. In the fifth O site, O(4) is bonded in a trigonal planar geometry to one Ca(2) and two equivalent Ca(1) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca6Si2O13
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.181
_cell_length_b   10.181
_cell_length_c   7.580
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   680.400
_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  0.666  0.621  0.622  1.0
  Ca  Ca1  1  0.955  0.334  0.622  1.0
  Ca  Ca2  1  0.379  0.045  0.622  1.0
  Ca  Ca3  1  0.334  0.379  0.378  1.0
  Ca  Ca4  1  0.045  0.666  0.378  1.0
  Ca  Ca5  1  0.621  0.955  0.378  1.0
  Ca  Ca6  1  0.335  0.382  0.870  1.0
  Ca  Ca7  1  0.047  0.665  0.870  1.0
  Ca  Ca8  1  0.618  0.953  0.870  1.0
  Ca  Ca9  1  0.382  0.047  0.130  1.0
  Ca  Ca10  1  0.665  0.618  0.130  1.0
  Ca  Ca11  1  0.953  0.335  0.130  1.0
  Si  Si12  1  0.333  0.667  0.656  1.0
  Si  Si13  1  0.667  0.333  0.344  1.0
  Si  Si14  1  0.333  0.667  0.094  1.0
  Si  Si15  1  0.667  0.333  0.906  1.0
  O  O16  1  0.412  0.565  0.147  1.0
  O  O17  1  0.153  0.588  0.147  1.0
  O  O18  1  0.435  0.847  0.147  1.0
  O  O19  1  0.586  0.433  0.397  1.0
  O  O20  1  0.847  0.414  0.397  1.0
  O  O21  1  0.567  0.153  0.397  1.0
  O  O22  1  0.414  0.567  0.603  1.0
  O  O23  1  0.153  0.586  0.603  1.0
  O  O24  1  0.433  0.847  0.603  1.0
  O  O25  1  0.236  0.917  0.881  1.0
  O  O26  1  0.682  0.764  0.881  1.0
  O  O27  1  0.083  0.318  0.881  1.0
  O  O28  1  0.229  0.928  0.369  1.0
  O  O29  1  0.699  0.771  0.369  1.0
  O  O30  1  0.072  0.301  0.369  1.0
  O  O31  1  0.318  0.236  0.119  1.0
  O  O32  1  0.917  0.682  0.119  1.0
  O  O33  1  0.764  0.083  0.119  1.0
  O  O34  1  0.333  0.667  0.875  1.0
  O  O35  1  0.667  0.333  0.125  1.0
  O  O36  1  0.301  0.229  0.631  1.0
  O  O37  1  0.928  0.699  0.631  1.0
  O  O38  1  0.771  0.072  0.631  1.0
  O  O39  1  0.588  0.435  0.853  1.0
  O  O40  1  0.847  0.412  0.853  1.0
  O  O41  1  0.565  0.153  0.853  1.0
[/CIF]
.