The structure described by Ca2SiO5 crystallizes in the triclinic P1 space group. There are six inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(11), one O(4), one O(9), two equivalent O(5), and two equivalent O(7) atoms to form distorted CaO7 pentagonal bipyramids that share  a cornercorner with one Ca(4)O6 octahedra, corners with two equivalent Ca(5)O6 octahedra, corners with two equivalent Si(2)O5 trigonal bipyramids, edges with two equivalent Ca(6)O6 octahedra, and edges with two equivalent Ca(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 29-56°. In the second Ca site, Ca(2) is bonded to one O(10), one O(12), one O(3), two equivalent O(6), and two equivalent O(8) atoms to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Ca(6)O6 octahedra, corners with two equivalent Si(3)O4 tetrahedra, edges with two equivalent Ca(4)O6 octahedra, edges with two equivalent Ca(5)O6 octahedra, edges with two equivalent Ca(2)O7 pentagonal bipyramids, and  an edgeedge with one Si(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 62-63°. In the third Ca site, Ca(3) is bonded in a 6-coordinate geometry to one O(3), one O(7), two equivalent O(1), and two equivalent O(9) atoms. In the fourth Ca site, Ca(4) is bonded to one O(4), one O(8), two equivalent O(10), and two equivalent O(2) atoms to form CaO6 octahedra that share  a cornercorner with one Ca(1)O7 pentagonal bipyramid, corners with two equivalent Si(3)O4 tetrahedra, corners with two equivalent Si(1)O5 trigonal bipyramids, edges with two equivalent Ca(4)O6 octahedra, edges with two equivalent Ca(6)O6 octahedra, and edges with two equivalent Ca(2)O7 pentagonal bipyramids. In the fifth Ca site, Ca(5) is bonded to one O(1), one O(6), two equivalent O(11), and two equivalent O(3) atoms to form CaO6 octahedra that share corners with two equivalent Ca(1)O7 pentagonal bipyramids,  a cornercorner with one Si(3)O4 tetrahedra,  a cornercorner with one Si(2)O5 trigonal bipyramid, edges with two equivalent Ca(5)O6 octahedra, and edges with two equivalent Ca(2)O7 pentagonal bipyramids. In the sixth Ca site, Ca(6) is bonded to one O(2), one O(5), two equivalent O(12), and two equivalent O(4) atoms to form CaO6 octahedra that share corners with two equivalent Ca(2)O7 pentagonal bipyramids,  a cornercorner with one Si(3)O4 tetrahedra,  a cornercorner with one Si(2)O5 trigonal bipyramid, corners with two equivalent Si(1)O5 trigonal bipyramids, edges with two equivalent Ca(4)O6 octahedra, edges with two equivalent Ca(6)O6 octahedra, and edges with two equivalent Ca(1)O7 pentagonal bipyramids. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(10), one O(12), one O(13), and two equivalent O(15) atoms to form distorted SiO5 trigonal bipyramids that share corners with two equivalent Ca(4)O6 octahedra, corners with two equivalent Ca(6)O6 octahedra, corners with two equivalent Si(1)O5 trigonal bipyramids,  an edgeedge with one Ca(2)O7 pentagonal bipyramid, and edges with two equivalent Si(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 51-64°. In the second Si site, Si(2) is bonded to one O(1), one O(15), one O(5), and two equivalent O(13) atoms to form distorted SiO5 trigonal bipyramids that share  a cornercorner with one Ca(5)O6 octahedra,  a cornercorner with one Ca(6)O6 octahedra, corners with two equivalent Ca(1)O7 pentagonal bipyramids, corners with two equivalent Si(2)O5 trigonal bipyramids, and edges with two equivalent Si(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 61-70°. In the third Si site, Si(3) is bonded to one O(2), one O(6), and two equivalent O(14) atoms to form distorted SiO4 tetrahedra that share  a cornercorner with one Ca(5)O6 octahedra,  a cornercorner with one Ca(6)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra, corners with two equivalent Ca(2)O7 pentagonal bipyramids, and corners with two equivalent Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-69°. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded to one Ca(5), two equivalent Ca(3), and one Si(2) atom to form distorted corner-sharing OCa3Si tetrahedra. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ca(6), two equivalent Ca(4), and one Si(3) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Ca(2), one Ca(3), and two equivalent Ca(5) atoms. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(4), and two equivalent Ca(6) atoms to form distorted OCa4 trigonal pyramids that share corners with two equivalent O(12)Ca3Si tetrahedra, corners with two equivalent O(4)Ca4 trigonal pyramids, and  an edgeedge with one O(12)Ca3Si tetrahedra. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Ca(6), two equivalent Ca(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Ca(5), two equivalent Ca(2), and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(3) and two equivalent Ca(1) atoms. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Ca(4) and two equivalent Ca(2) atoms. In the ninth O site, O(9) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ca(3) atoms. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(4), and one Si(1) atom. In the eleventh O site, O(11) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ca(5) atoms. In the twelfth O site, O(12) is bonded to one Ca(2), two equivalent Ca(6), and one Si(1) atom to form distorted OCa3Si tetrahedra that share corners with two equivalent O(12)Ca3Si tetrahedra, corners with two equivalent O(4)Ca4 trigonal pyramids, and  an edgeedge with one O(4)Ca4 trigonal pyramid. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to one Si(1) and two equivalent Si(2) atoms. In the fourteenth O site, O(14) is bonded in a distorted bent 120 degrees geometry to two equivalent Si(3) atoms. In the fifteenth O site, O(15) is bonded in a distorted T-shaped geometry to one Si(2) and two equivalent Si(1) atoms. is represented by the CIF file [CIF]
data_Ca2SiO5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.503
_cell_length_b   8.703
_cell_length_c   11.345
_cell_angle_alpha   87.050
_cell_angle_beta   90.077
_cell_angle_gamma   78.522
_symmetry_Int_Tables_number   1
_cell_volume   338.437
_cell_formula_units_Z   3
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  0.897  0.186  0.443  1.0
  Ca  Ca1  1  0.079  0.812  0.956  1.0
  Ca  Ca2  1  0.208  0.569  0.596  1.0
  Ca  Ca3  1  0.767  0.441  0.077  1.0
  Ca  Ca4  1  0.544  0.901  0.699  1.0
  Ca  Ca5  1  0.444  0.098  0.186  1.0
  Si  Si6  1  0.115  0.750  0.220  1.0
  Si  Si7  1  0.582  0.818  0.403  1.0
  Si  Si8  1  0.343  0.182  0.892  1.0
  O  O9  1  0.623  0.738  0.539  1.0
  O  O10  1  0.351  0.274  0.012  1.0
  O  O11  1  0.128  0.725  0.764  1.0
  O  O12  1  0.866  0.254  0.235  1.0
  O  O13  1  0.486  0.010  0.391  1.0
  O  O14  1  0.491  0.994  0.895  1.0
  O  O15  1  0.301  0.378  0.455  1.0
  O  O16  1  0.663  0.644  0.899  1.0
  O  O17  1  0.800  0.384  0.583  1.0
  O  O18  1  0.183  0.610  0.126  1.0
  O  O19  1  0.971  0.049  0.626  1.0
  O  O20  1  0.031  0.920  0.144  1.0
  O  O21  1  0.102  0.777  0.375  1.0
  O  O22  1  0.889  0.228  0.835  1.0
  O  O23  1  0.621  0.738  0.261  1.0
[/CIF]
.
The structure described by Ca2SiO5 crystallizes in the triclinic P1 space group. There are six inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(11), one O(4), one O(9), two equivalent O(5), and two equivalent O(7) atoms to form distorted CaO7 pentagonal bipyramids that share  a cornercorner with one Ca(4)O6 octahedra, corners with two equivalent Ca(5)O6 octahedra, corners with two equivalent Si(2)O5 trigonal bipyramids, edges with two equivalent Ca(6)O6 octahedra, and edges with two equivalent Ca(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 29-56°. In the second Ca site, Ca(2) is bonded to one O(10), one O(12), one O(3), two equivalent O(6), and two equivalent O(8) atoms to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Ca(6)O6 octahedra, corners with two equivalent Si(3)O4 tetrahedra, edges with two equivalent Ca(4)O6 octahedra, edges with two equivalent Ca(5)O6 octahedra, edges with two equivalent Ca(2)O7 pentagonal bipyramids, and  an edgeedge with one Si(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 62-63°. In the third Ca site, Ca(3) is bonded in a 6-coordinate geometry to one O(3), one O(7), two equivalent O(1), and two equivalent O(9) atoms. In the fourth Ca site, Ca(4) is bonded to one O(4), one O(8), two equivalent O(10), and two equivalent O(2) atoms to form CaO6 octahedra that share  a cornercorner with one Ca(1)O7 pentagonal bipyramid, corners with two equivalent Si(3)O4 tetrahedra, corners with two equivalent Si(1)O5 trigonal bipyramids, edges with two equivalent Ca(4)O6 octahedra, edges with two equivalent Ca(6)O6 octahedra, and edges with two equivalent Ca(2)O7 pentagonal bipyramids. In the fifth Ca site, Ca(5) is bonded to one O(1), one O(6), two equivalent O(11), and two equivalent O(3) atoms to form CaO6 octahedra that share corners with two equivalent Ca(1)O7 pentagonal bipyramids,  a cornercorner with one Si(3)O4 tetrahedra,  a cornercorner with one Si(2)O5 trigonal bipyramid, edges with two equivalent Ca(5)O6 octahedra, and edges with two equivalent Ca(2)O7 pentagonal bipyramids. In the sixth Ca site, Ca(6) is bonded to one O(2), one O(5), two equivalent O(12), and two equivalent O(4) atoms to form CaO6 octahedra that share corners with two equivalent Ca(2)O7 pentagonal bipyramids,  a cornercorner with one Si(3)O4 tetrahedra,  a cornercorner with one Si(2)O5 trigonal bipyramid, corners with two equivalent Si(1)O5 trigonal bipyramids, edges with two equivalent Ca(4)O6 octahedra, edges with two equivalent Ca(6)O6 octahedra, and edges with two equivalent Ca(1)O7 pentagonal bipyramids. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(10), one O(12), one O(13), and two equivalent O(15) atoms to form distorted SiO5 trigonal bipyramids that share corners with two equivalent Ca(4)O6 octahedra, corners with two equivalent Ca(6)O6 octahedra, corners with two equivalent Si(1)O5 trigonal bipyramids,  an edgeedge with one Ca(2)O7 pentagonal bipyramid, and edges with two equivalent Si(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 51-64°. In the second Si site, Si(2) is bonded to one O(1), one O(15), one O(5), and two equivalent O(13) atoms to form distorted SiO5 trigonal bipyramids that share  a cornercorner with one Ca(5)O6 octahedra,  a cornercorner with one Ca(6)O6 octahedra, corners with two equivalent Ca(1)O7 pentagonal bipyramids, corners with two equivalent Si(2)O5 trigonal bipyramids, and edges with two equivalent Si(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 61-70°. In the third Si site, Si(3) is bonded to one O(2), one O(6), and two equivalent O(14) atoms to form distorted SiO4 tetrahedra that share  a cornercorner with one Ca(5)O6 octahedra,  a cornercorner with one Ca(6)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra, corners with two equivalent Ca(2)O7 pentagonal bipyramids, and corners with two equivalent Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-69°. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded to one Ca(5), two equivalent Ca(3), and one Si(2) atom to form distorted corner-sharing OCa3Si tetrahedra. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ca(6), two equivalent Ca(4), and one Si(3) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Ca(2), one Ca(3), and two equivalent Ca(5) atoms. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(4), and two equivalent Ca(6) atoms to form distorted OCa4 trigonal pyramids that share corners with two equivalent O(12)Ca3Si tetrahedra, corners with two equivalent O(4)Ca4 trigonal pyramids, and  an edgeedge with one O(12)Ca3Si tetrahedra. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Ca(6), two equivalent Ca(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Ca(5), two equivalent Ca(2), and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(3) and two equivalent Ca(1) atoms. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Ca(4) and two equivalent Ca(2) atoms. In the ninth O site, O(9) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ca(3) atoms. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(4), and one Si(1) atom. In the eleventh O site, O(11) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ca(5) atoms. In the twelfth O site, O(12) is bonded to one Ca(2), two equivalent Ca(6), and one Si(1) atom to form distorted OCa3Si tetrahedra that share corners with two equivalent O(12)Ca3Si tetrahedra, corners with two equivalent O(4)Ca4 trigonal pyramids, and  an edgeedge with one O(4)Ca4 trigonal pyramid. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to one Si(1) and two equivalent Si(2) atoms. In the fourteenth O site, O(14) is bonded in a distorted bent 120 degrees geometry to two equivalent Si(3) atoms. In the fifteenth O site, O(15) is bonded in a distorted T-shaped geometry to one Si(2) and two equivalent Si(1) atoms. is represented by the CIF file [CIF]
data_Ca2SiO5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.503
_cell_length_b   8.703
_cell_length_c   11.345
_cell_angle_alpha   87.050
_cell_angle_beta   90.077
_cell_angle_gamma   78.522
_symmetry_Int_Tables_number   1
_cell_volume   338.437
_cell_formula_units_Z   3
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  0.897  0.186  0.443  1.0
  Ca  Ca1  1  0.079  0.812  0.956  1.0
  Ca  Ca2  1  0.208  0.569  0.596  1.0
  Ca  Ca3  1  0.767  0.441  0.077  1.0
  Ca  Ca4  1  0.544  0.901  0.699  1.0
  Ca  Ca5  1  0.444  0.098  0.186  1.0
  Si  Si6  1  0.115  0.750  0.220  1.0
  Si  Si7  1  0.582  0.818  0.403  1.0
  Si  Si8  1  0.343  0.182  0.892  1.0
  O  O9  1  0.623  0.738  0.539  1.0
  O  O10  1  0.351  0.274  0.012  1.0
  O  O11  1  0.128  0.725  0.764  1.0
  O  O12  1  0.866  0.254  0.235  1.0
  O  O13  1  0.486  0.010  0.391  1.0
  O  O14  1  0.491  0.994  0.895  1.0
  O  O15  1  0.301  0.378  0.455  1.0
  O  O16  1  0.663  0.644  0.899  1.0
  O  O17  1  0.800  0.384  0.583  1.0
  O  O18  1  0.183  0.610  0.126  1.0
  O  O19  1  0.971  0.049  0.626  1.0
  O  O20  1  0.031  0.920  0.144  1.0
  O  O21  1  0.102  0.777  0.375  1.0
  O  O22  1  0.889  0.228  0.835  1.0
  O  O23  1  0.621  0.738  0.261  1.0
[/CIF]
.