The compound described by Ca2Mg5(SiO3)8 is Esseneite-like structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with two equivalent Mg(3)O6 octahedra. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra, and edges with two equivalent Mg(1)O6 octahedra. In the third Mg site, Mg(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 58-61°. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-57°. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Mg(1), one Mg(2), and one Si(2) atom. In the second O site, O(3) is bonded in a trigonal non-coplanar geometry to one Mg(3) and two equivalent Mg(1) atoms. In the third O site, O(4) is bonded in a distorted T-shaped geometry to one Ca(1), one Mg(2), and one Si(2) atom. In the fourth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the fifth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(7) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the seventh O site, O(1) is bonded to one Mg(1), one Mg(2), one Mg(3), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OMg3Si trigonal pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Mg5(SiO3)8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.462
_cell_length_b   10.462
_cell_length_c   5.335
_cell_angle_alpha   83.098
_cell_angle_beta   83.098
_cell_angle_gamma   122.923
_symmetry_Int_Tables_number   1
_cell_volume   474.444
_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
  Ca  Ca0  1  0.721  0.279  0.500  1.0
  Ca  Ca1  1  0.279  0.721  0.500  1.0
  Mg  Mg2  1  0.906  0.094  0.500  1.0
  Mg  Mg3  1  0.094  0.906  0.500  1.0
  Mg  Mg4  1  0.822  0.178  0.000  1.0
  Mg  Mg5  1  0.178  0.822  0.000  1.0
  Mg  Mg6  1  0.000  0.000  0.000  1.0
  Si  Si7  1  0.195  0.363  0.707  1.0
  Si  Si8  1  0.363  0.195  0.707  1.0
  Si  Si9  1  0.805  0.637  0.293  1.0
  Si  Si10  1  0.637  0.805  0.293  1.0
  Si  Si11  1  0.118  0.459  0.198  1.0
  Si  Si12  1  0.459  0.118  0.198  1.0
  Si  Si13  1  0.882  0.541  0.802  1.0
  Si  Si14  1  0.541  0.882  0.802  1.0
  O  O15  1  0.024  0.199  0.789  1.0
  O  O16  1  0.199  0.024  0.789  1.0
  O  O17  1  0.976  0.801  0.211  1.0
  O  O18  1  0.801  0.976  0.211  1.0
  O  O19  1  0.947  0.292  0.276  1.0
  O  O20  1  0.292  0.947  0.276  1.0
  O  O21  1  0.053  0.708  0.724  1.0
  O  O22  1  0.708  0.053  0.724  1.0
  O  O23  1  0.085  0.085  0.319  1.0
  O  O24  1  0.915  0.915  0.681  1.0
  O  O25  1  0.121  0.614  0.206  1.0
  O  O26  1  0.614  0.121  0.206  1.0
  O  O27  1  0.879  0.386  0.794  1.0
  O  O28  1  0.386  0.879  0.794  1.0
  O  O29  1  0.213  0.478  0.906  1.0
  O  O30  1  0.478  0.213  0.906  1.0
  O  O31  1  0.787  0.522  0.094  1.0
  O  O32  1  0.522  0.787  0.094  1.0
  O  O33  1  0.222  0.462  0.418  1.0
  O  O34  1  0.462  0.222  0.418  1.0
  O  O35  1  0.778  0.538  0.582  1.0
  O  O36  1  0.538  0.778  0.582  1.0
  O  O37  1  0.334  0.334  0.705  1.0
  O  O38  1  0.666  0.666  0.295  1.0
[/CIF]
.
The compound described by Ca2Mg5(SiO3)8 is Esseneite-like structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with two equivalent Mg(3)O6 octahedra. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra, and edges with two equivalent Mg(1)O6 octahedra. In the third Mg site, Mg(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 58-61°. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-57°. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Mg(1), one Mg(2), and one Si(2) atom. In the second O site, O(3) is bonded in a trigonal non-coplanar geometry to one Mg(3) and two equivalent Mg(1) atoms. In the third O site, O(4) is bonded in a distorted T-shaped geometry to one Ca(1), one Mg(2), and one Si(2) atom. In the fourth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the fifth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(7) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the seventh O site, O(1) is bonded to one Mg(1), one Mg(2), one Mg(3), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OMg3Si trigonal pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Mg5(SiO3)8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.462
_cell_length_b   10.462
_cell_length_c   5.335
_cell_angle_alpha   83.098
_cell_angle_beta   83.098
_cell_angle_gamma   122.923
_symmetry_Int_Tables_number   1
_cell_volume   474.444
_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
  Ca  Ca0  1  0.721  0.279  0.500  1.0
  Ca  Ca1  1  0.279  0.721  0.500  1.0
  Mg  Mg2  1  0.906  0.094  0.500  1.0
  Mg  Mg3  1  0.094  0.906  0.500  1.0
  Mg  Mg4  1  0.822  0.178  0.000  1.0
  Mg  Mg5  1  0.178  0.822  0.000  1.0
  Mg  Mg6  1  0.000  0.000  0.000  1.0
  Si  Si7  1  0.195  0.363  0.707  1.0
  Si  Si8  1  0.363  0.195  0.707  1.0
  Si  Si9  1  0.805  0.637  0.293  1.0
  Si  Si10  1  0.637  0.805  0.293  1.0
  Si  Si11  1  0.118  0.459  0.198  1.0
  Si  Si12  1  0.459  0.118  0.198  1.0
  Si  Si13  1  0.882  0.541  0.802  1.0
  Si  Si14  1  0.541  0.882  0.802  1.0
  O  O15  1  0.024  0.199  0.789  1.0
  O  O16  1  0.199  0.024  0.789  1.0
  O  O17  1  0.976  0.801  0.211  1.0
  O  O18  1  0.801  0.976  0.211  1.0
  O  O19  1  0.947  0.292  0.276  1.0
  O  O20  1  0.292  0.947  0.276  1.0
  O  O21  1  0.053  0.708  0.724  1.0
  O  O22  1  0.708  0.053  0.724  1.0
  O  O23  1  0.085  0.085  0.319  1.0
  O  O24  1  0.915  0.915  0.681  1.0
  O  O25  1  0.121  0.614  0.206  1.0
  O  O26  1  0.614  0.121  0.206  1.0
  O  O27  1  0.879  0.386  0.794  1.0
  O  O28  1  0.386  0.879  0.794  1.0
  O  O29  1  0.213  0.478  0.906  1.0
  O  O30  1  0.478  0.213  0.906  1.0
  O  O31  1  0.787  0.522  0.094  1.0
  O  O32  1  0.522  0.787  0.094  1.0
  O  O33  1  0.222  0.462  0.418  1.0
  O  O34  1  0.462  0.222  0.418  1.0
  O  O35  1  0.778  0.538  0.582  1.0
  O  O36  1  0.538  0.778  0.582  1.0
  O  O37  1  0.334  0.334  0.705  1.0
  O  O38  1  0.666  0.666  0.295  1.0
[/CIF]
.