The material described by MgSi2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(1), one Si(2), two equivalent Si(3), and two equivalent Si(4) atoms to form distorted MgSi6 octahedra that share  a cornercorner with one Si(4)Mg3Si3 octahedra, corners with two equivalent Si(8)Mg3Si3 octahedra, and edges with two equivalent Mg(1)Si6 octahedra. The corner-sharing octahedral tilt angles range from 23-116°. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(2), one Si(5), one Si(6), one Si(8), and two equivalent Si(7) atoms. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to one Si(1), one Si(3), one Si(4), and two equivalent Si(2) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(3), one Si(5), one Si(7), two equivalent Si(6), and two equivalent Si(8) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(3), one Si(4), and two equivalent Si(8) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(3), one Si(6), and two equivalent Si(7) atoms. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to one Mg(3), one Mg(4), two equivalent Mg(1), one Si(7), and two equivalent Si(6) atoms. In the fourth Si site, Si(4) is bonded to one Mg(3), two equivalent Mg(1), one Si(1), and two equivalent Si(5) atoms to form distorted SiMg3Si3 octahedra that share  a cornercorner with one Mg(1)Si6 octahedra, corners with four equivalent Si(8)Mg3Si3 octahedra, and edges with two equivalent Si(4)Mg3Si3 octahedra. The corner-sharing octahedral tilt angles range from 62-116°. In the fifth Si site, Si(5) is bonded in a 5-coordinate geometry to one Mg(2), one Mg(4), one Si(8), and two equivalent Si(4) atoms. In the sixth Si site, Si(6) is bonded in a 6-coordinate geometry to one Mg(2), two equivalent Mg(4), one Si(2), and two equivalent Si(3) atoms. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(4), two equivalent Mg(2), one Si(3), and two equivalent Si(2) atoms. In the eighth Si site, Si(8) is bonded to one Mg(2), two equivalent Mg(4), one Si(5), and two equivalent Si(1) atoms to form distorted SiMg3Si3 octahedra that share corners with two equivalent Mg(1)Si6 octahedra, corners with four equivalent Si(4)Mg3Si3 octahedra, and edges with two equivalent Si(8)Mg3Si3 octahedra. The corner-sharing octahedral tilt angles range from 23-81°. is represented by the CIF card [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.763
_cell_length_b   6.284
_cell_length_c   10.374
_cell_angle_alpha   102.502
_cell_angle_beta   93.765
_cell_angle_gamma   90.050
_symmetry_Int_Tables_number   1
_cell_volume   238.935
_cell_formula_units_Z   4
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
  Mg  Mg0  1  0.566  0.687  0.011  1.0
  Mg  Mg1  1  0.616  0.532  0.496  1.0
  Mg  Mg2  1  0.045  0.219  0.000  1.0
  Mg  Mg3  1  0.109  0.997  0.489  1.0
  Si  Si4  1  0.150  0.860  0.811  1.0
  Si  Si5  1  0.572  0.394  0.201  1.0
  Si  Si6  1  0.086  0.897  0.202  1.0
  Si  Si7  1  0.040  0.481  0.814  1.0
  Si  Si8  1  0.514  0.315  0.690  1.0
  Si  Si9  1  0.603  0.095  0.301  1.0
  Si  Si10  1  0.089  0.592  0.300  1.0
  Si  Si11  1  0.625  0.932  0.685  1.0
[/CIF]
.
The material described by MgSi2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(1), one Si(2), two equivalent Si(3), and two equivalent Si(4) atoms to form distorted MgSi6 octahedra that share  a cornercorner with one Si(4)Mg3Si3 octahedra, corners with two equivalent Si(8)Mg3Si3 octahedra, and edges with two equivalent Mg(1)Si6 octahedra. The corner-sharing octahedral tilt angles range from 23-116°. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(2), one Si(5), one Si(6), one Si(8), and two equivalent Si(7) atoms. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to one Si(1), one Si(3), one Si(4), and two equivalent Si(2) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(3), one Si(5), one Si(7), two equivalent Si(6), and two equivalent Si(8) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(3), one Si(4), and two equivalent Si(8) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(3), one Si(6), and two equivalent Si(7) atoms. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to one Mg(3), one Mg(4), two equivalent Mg(1), one Si(7), and two equivalent Si(6) atoms. In the fourth Si site, Si(4) is bonded to one Mg(3), two equivalent Mg(1), one Si(1), and two equivalent Si(5) atoms to form distorted SiMg3Si3 octahedra that share  a cornercorner with one Mg(1)Si6 octahedra, corners with four equivalent Si(8)Mg3Si3 octahedra, and edges with two equivalent Si(4)Mg3Si3 octahedra. The corner-sharing octahedral tilt angles range from 62-116°. In the fifth Si site, Si(5) is bonded in a 5-coordinate geometry to one Mg(2), one Mg(4), one Si(8), and two equivalent Si(4) atoms. In the sixth Si site, Si(6) is bonded in a 6-coordinate geometry to one Mg(2), two equivalent Mg(4), one Si(2), and two equivalent Si(3) atoms. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(4), two equivalent Mg(2), one Si(3), and two equivalent Si(2) atoms. In the eighth Si site, Si(8) is bonded to one Mg(2), two equivalent Mg(4), one Si(5), and two equivalent Si(1) atoms to form distorted SiMg3Si3 octahedra that share corners with two equivalent Mg(1)Si6 octahedra, corners with four equivalent Si(4)Mg3Si3 octahedra, and edges with two equivalent Si(8)Mg3Si3 octahedra. The corner-sharing octahedral tilt angles range from 23-81°. is represented by the CIF card [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.763
_cell_length_b   6.284
_cell_length_c   10.374
_cell_angle_alpha   102.502
_cell_angle_beta   93.765
_cell_angle_gamma   90.050
_symmetry_Int_Tables_number   1
_cell_volume   238.935
_cell_formula_units_Z   4
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
  Mg  Mg0  1  0.566  0.687  0.011  1.0
  Mg  Mg1  1  0.616  0.532  0.496  1.0
  Mg  Mg2  1  0.045  0.219  0.000  1.0
  Mg  Mg3  1  0.109  0.997  0.489  1.0
  Si  Si4  1  0.150  0.860  0.811  1.0
  Si  Si5  1  0.572  0.394  0.201  1.0
  Si  Si6  1  0.086  0.897  0.202  1.0
  Si  Si7  1  0.040  0.481  0.814  1.0
  Si  Si8  1  0.514  0.315  0.690  1.0
  Si  Si9  1  0.603  0.095  0.301  1.0
  Si  Si10  1  0.089  0.592  0.300  1.0
  Si  Si11  1  0.625  0.932  0.685  1.0
[/CIF]
.