The material described by K2Ca2Si8O23 crystallizes in the monoclinic C2 space group. K(1) is bonded in a 6-coordinate geometry to one O(11), one O(12), one O(3), one O(4), one O(5), and one O(9) atom. Ca(1) is bonded to one O(12), one O(7), two equivalent O(4), and two equivalent O(8) atoms to form distorted CaO6 octahedra that share  a cornercorner with one Si(3)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra, and edges with two equivalent Ca(1)O6 octahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(10), one O(2), and one O(6) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-58°. In the third Si site, Si(3) is bonded to one O(2), one O(5), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 44°. In the fourth Si site, Si(4) is bonded to one O(10), one O(3), one O(8), and one O(9) atom to form SiO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-54°. There are twelve inequivalent O sites. In the first O site, O(6) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ca(1) and one Si(3) atom. In the third O site, O(8) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one Si(4) atom. In the fourth O site, O(9) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(3), and one Si(4) atom. In the fifth O site, O(10) is bonded in a distorted bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the sixth O site, O(11) is bonded in a bent 150 degrees geometry to one K(1) and one O(11) atom. In the seventh O site, O(12) is bonded in an L-shaped geometry to one K(1) and one Ca(1) atom. In the eighth O site, O(1) is bonded in a linear geometry to two equivalent Si(1) atoms. In the ninth O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the tenth O site, O(3) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(4) atom. In the eleventh O site, O(4) is bonded in a 3-coordinate geometry to one K(1), two equivalent Ca(1), and one Si(2) atom. In the twelfth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(3) atom. is represented by the CIF file [CIF]
data_K2Ca2Si8O23
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.559
_cell_length_b   7.143
_cell_length_c   12.770
_cell_angle_alpha   106.242
_cell_angle_beta   97.684
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   568.826
_cell_formula_units_Z   1
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
  K  K0  1  0.279  0.138  0.263  1.0
  K  K1  1  0.721  0.875  0.737  1.0
  Ca  Ca2  1  0.961  0.258  0.518  1.0
  Ca  Ca3  1  0.039  0.740  0.482  1.0
  Si  Si4  1  0.005  0.435  0.869  1.0
  Si  Si5  1  0.995  0.566  0.131  1.0
  Si  Si6  1  0.221  0.084  0.733  1.0
  Si  Si7  1  0.779  0.352  0.267  1.0
  Si  Si8  1  0.575  0.353  0.706  1.0
  Si  Si9  1  0.425  0.647  0.294  1.0
  Si  Si10  1  0.222  0.652  0.736  1.0
  Si  Si11  1  0.778  0.916  0.264  1.0
  O  O12  1  0.000  0.501  0.000  1.0
  O  O13  1  0.774  0.376  0.803  1.0
  O  O14  1  0.226  0.573  0.197  1.0
  O  O15  1  0.278  0.888  0.772  1.0
  O  O16  1  0.722  0.116  0.228  1.0
  O  O17  1  0.051  0.039  0.625  1.0
  O  O18  1  0.949  0.414  0.375  1.0
  O  O19  1  0.445  0.163  0.715  1.0
  O  O20  1  0.555  0.449  0.285  1.0
  O  O21  1  0.146  0.244  0.840  1.0
  O  O22  1  0.854  0.404  0.160  1.0
  O  O23  1  0.651  0.323  0.588  1.0
  O  O24  1  0.349  0.735  0.412  1.0
  O  O25  1  0.084  0.576  0.619  1.0
  O  O26  1  0.916  0.957  0.381  1.0
  O  O27  1  0.449  0.554  0.745  1.0
  O  O28  1  0.551  0.809  0.255  1.0
  O  O29  1  0.099  0.619  0.835  1.0
  O  O30  1  0.901  0.783  0.165  1.0
  O  O31  1  0.423  0.921  0.024  1.0
  O  O32  1  0.577  0.898  0.976  1.0
  O  O33  1  0.351  0.238  0.489  1.0
  O  O34  1  0.649  0.749  0.511  1.0
[/CIF]
.
The material described by K2Ca2Si8O23 crystallizes in the monoclinic C2 space group. K(1) is bonded in a 6-coordinate geometry to one O(11), one O(12), one O(3), one O(4), one O(5), and one O(9) atom. Ca(1) is bonded to one O(12), one O(7), two equivalent O(4), and two equivalent O(8) atoms to form distorted CaO6 octahedra that share  a cornercorner with one Si(3)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra, and edges with two equivalent Ca(1)O6 octahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(10), one O(2), and one O(6) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-58°. In the third Si site, Si(3) is bonded to one O(2), one O(5), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 44°. In the fourth Si site, Si(4) is bonded to one O(10), one O(3), one O(8), and one O(9) atom to form SiO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-54°. There are twelve inequivalent O sites. In the first O site, O(6) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ca(1) and one Si(3) atom. In the third O site, O(8) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one Si(4) atom. In the fourth O site, O(9) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(3), and one Si(4) atom. In the fifth O site, O(10) is bonded in a distorted bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the sixth O site, O(11) is bonded in a bent 150 degrees geometry to one K(1) and one O(11) atom. In the seventh O site, O(12) is bonded in an L-shaped geometry to one K(1) and one Ca(1) atom. In the eighth O site, O(1) is bonded in a linear geometry to two equivalent Si(1) atoms. In the ninth O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the tenth O site, O(3) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(4) atom. In the eleventh O site, O(4) is bonded in a 3-coordinate geometry to one K(1), two equivalent Ca(1), and one Si(2) atom. In the twelfth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(3) atom. is represented by the CIF file [CIF]
data_K2Ca2Si8O23
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.559
_cell_length_b   7.143
_cell_length_c   12.770
_cell_angle_alpha   106.242
_cell_angle_beta   97.684
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   568.826
_cell_formula_units_Z   1
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
  K  K0  1  0.279  0.138  0.263  1.0
  K  K1  1  0.721  0.875  0.737  1.0
  Ca  Ca2  1  0.961  0.258  0.518  1.0
  Ca  Ca3  1  0.039  0.740  0.482  1.0
  Si  Si4  1  0.005  0.435  0.869  1.0
  Si  Si5  1  0.995  0.566  0.131  1.0
  Si  Si6  1  0.221  0.084  0.733  1.0
  Si  Si7  1  0.779  0.352  0.267  1.0
  Si  Si8  1  0.575  0.353  0.706  1.0
  Si  Si9  1  0.425  0.647  0.294  1.0
  Si  Si10  1  0.222  0.652  0.736  1.0
  Si  Si11  1  0.778  0.916  0.264  1.0
  O  O12  1  0.000  0.501  0.000  1.0
  O  O13  1  0.774  0.376  0.803  1.0
  O  O14  1  0.226  0.573  0.197  1.0
  O  O15  1  0.278  0.888  0.772  1.0
  O  O16  1  0.722  0.116  0.228  1.0
  O  O17  1  0.051  0.039  0.625  1.0
  O  O18  1  0.949  0.414  0.375  1.0
  O  O19  1  0.445  0.163  0.715  1.0
  O  O20  1  0.555  0.449  0.285  1.0
  O  O21  1  0.146  0.244  0.840  1.0
  O  O22  1  0.854  0.404  0.160  1.0
  O  O23  1  0.651  0.323  0.588  1.0
  O  O24  1  0.349  0.735  0.412  1.0
  O  O25  1  0.084  0.576  0.619  1.0
  O  O26  1  0.916  0.957  0.381  1.0
  O  O27  1  0.449  0.554  0.745  1.0
  O  O28  1  0.551  0.809  0.255  1.0
  O  O29  1  0.099  0.619  0.835  1.0
  O  O30  1  0.901  0.783  0.165  1.0
  O  O31  1  0.423  0.921  0.024  1.0
  O  O32  1  0.577  0.898  0.976  1.0
  O  O33  1  0.351  0.238  0.489  1.0
  O  O34  1  0.649  0.749  0.511  1.0
[/CIF]
.