The structure described by Mg3Fe(SiO4)2 is Spinel-derived structured and crystallizes in the monoclinic P2_1/c space group. There are two 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(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-63°. In the second Mg site, Mg(2) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, corners with four equivalent Si(1)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-64°. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-64°. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Fe(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Mg(2)O6 octahedra, and  an edgeedge with one Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-61°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Mg(2), one Fe(1), and one Si(1) atom to form distorted corner-sharing OMg2FeSi trigonal pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(2), one Fe(1), and one Si(1) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(2), one Fe(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Mg(2), and one Si(1) atom. is represented by the CIF file [CIF]
data_Mg3Fe(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.381
_cell_length_b   4.848
_cell_length_c   7.751
_cell_angle_alpha   51.574
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   305.607
_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
  Mg  Mg0  1  0.500  0.000  0.500  1.0
  Mg  Mg1  1  0.000  0.000  0.000  1.0
  Mg  Mg2  1  0.778  0.260  0.249  1.0
  Mg  Mg3  1  0.278  0.740  0.251  1.0
  Mg  Mg4  1  0.222  0.740  0.751  1.0
  Mg  Mg5  1  0.722  0.260  0.749  1.0
  Fe  Fe6  1  0.500  0.500  0.000  1.0
  Fe  Fe7  1  0.000  0.500  0.500  1.0
  Si  Si8  1  0.595  0.823  0.251  1.0
  Si  Si9  1  0.095  0.177  0.249  1.0
  Si  Si10  1  0.405  0.177  0.749  1.0
  Si  Si11  1  0.905  0.823  0.751  1.0
  O  O12  1  0.593  0.482  0.253  1.0
  O  O13  1  0.093  0.518  0.247  1.0
  O  O14  1  0.407  0.518  0.747  1.0
  O  O15  1  0.907  0.482  0.753  1.0
  O  O16  1  0.948  0.040  0.246  1.0
  O  O17  1  0.448  0.960  0.254  1.0
  O  O18  1  0.052  0.960  0.754  1.0
  O  O19  1  0.552  0.040  0.746  1.0
  O  O20  1  0.666  0.180  0.035  1.0
  O  O21  1  0.166  0.820  0.465  1.0
  O  O22  1  0.337  0.244  0.533  1.0
  O  O23  1  0.837  0.756  0.967  1.0
  O  O24  1  0.334  0.820  0.965  1.0
  O  O25  1  0.834  0.180  0.535  1.0
  O  O26  1  0.663  0.756  0.467  1.0
  O  O27  1  0.163  0.244  0.033  1.0
[/CIF]
.
The structure described by Mg3Fe(SiO4)2 is Spinel-derived structured and crystallizes in the monoclinic P2_1/c space group. There are two 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(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-63°. In the second Mg site, Mg(2) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, corners with four equivalent Si(1)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-64°. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-64°. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Fe(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Mg(2)O6 octahedra, and  an edgeedge with one Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-61°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Mg(2), one Fe(1), and one Si(1) atom to form distorted corner-sharing OMg2FeSi trigonal pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(2), one Fe(1), and one Si(1) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(2), one Fe(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Mg(2), and one Si(1) atom. is represented by the CIF file [CIF]
data_Mg3Fe(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.381
_cell_length_b   4.848
_cell_length_c   7.751
_cell_angle_alpha   51.574
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   305.607
_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
  Mg  Mg0  1  0.500  0.000  0.500  1.0
  Mg  Mg1  1  0.000  0.000  0.000  1.0
  Mg  Mg2  1  0.778  0.260  0.249  1.0
  Mg  Mg3  1  0.278  0.740  0.251  1.0
  Mg  Mg4  1  0.222  0.740  0.751  1.0
  Mg  Mg5  1  0.722  0.260  0.749  1.0
  Fe  Fe6  1  0.500  0.500  0.000  1.0
  Fe  Fe7  1  0.000  0.500  0.500  1.0
  Si  Si8  1  0.595  0.823  0.251  1.0
  Si  Si9  1  0.095  0.177  0.249  1.0
  Si  Si10  1  0.405  0.177  0.749  1.0
  Si  Si11  1  0.905  0.823  0.751  1.0
  O  O12  1  0.593  0.482  0.253  1.0
  O  O13  1  0.093  0.518  0.247  1.0
  O  O14  1  0.407  0.518  0.747  1.0
  O  O15  1  0.907  0.482  0.753  1.0
  O  O16  1  0.948  0.040  0.246  1.0
  O  O17  1  0.448  0.960  0.254  1.0
  O  O18  1  0.052  0.960  0.754  1.0
  O  O19  1  0.552  0.040  0.746  1.0
  O  O20  1  0.666  0.180  0.035  1.0
  O  O21  1  0.166  0.820  0.465  1.0
  O  O22  1  0.337  0.244  0.533  1.0
  O  O23  1  0.837  0.756  0.967  1.0
  O  O24  1  0.334  0.820  0.965  1.0
  O  O25  1  0.834  0.180  0.535  1.0
  O  O26  1  0.663  0.756  0.467  1.0
  O  O27  1  0.163  0.244  0.033  1.0
[/CIF]
.