The crystal structure described by Mg3Ca crystallizes in the orthorhombic Imm2 space group. Ca(1) is bonded to two equivalent Ca(1), four equivalent Mg(1), and six equivalent Mg(2) atoms to form CaCa2Mg10 cuboctahedra that share corners with four equivalent Mg(1)Ca4Mg8 cuboctahedra, corners with fourteen equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with two equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with four equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Ca(1)Ca2Mg10 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Ca(1), two equivalent Mg(1), and six equivalent Mg(2) atoms to form distorted MgCa4Mg8 cuboctahedra that share corners with four equivalent Ca(1)Ca2Mg10 cuboctahedra, corners with fourteen equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with two equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with four equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Mg(1)Ca4Mg8 cuboctahedra, faces with six equivalent Ca(1)Ca2Mg10 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded to three equivalent Ca(1), three equivalent Mg(1), and six equivalent Mg(2) atoms to form distorted MgCa3Mg9 cuboctahedra that share corners with eighteen equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with six equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Mg(1)Ca4Mg8 cuboctahedra, faces with six equivalent Ca(1)Ca2Mg10 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with eight equivalent Mg(2)Ca3Mg9 cuboctahedra. is represented by the CIF card [CIF]
data_CaMg3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.462
_cell_length_b   6.462
_cell_length_c   6.462
_cell_angle_alpha   149.791
_cell_angle_beta   126.328
_cell_angle_gamma   62.831
_symmetry_Int_Tables_number   1
_cell_volume   108.360
_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  0.337  0.000  0.337  1.0
  Mg  Mg1  1  0.831  0.500  0.331  1.0
  Mg  Mg2  1  0.244  0.245  0.999  1.0
  Mg  Mg3  1  0.754  0.755  0.999  1.0
[/CIF]
.
The crystal structure described by Mg3Ca crystallizes in the orthorhombic Imm2 space group. Ca(1) is bonded to two equivalent Ca(1), four equivalent Mg(1), and six equivalent Mg(2) atoms to form CaCa2Mg10 cuboctahedra that share corners with four equivalent Mg(1)Ca4Mg8 cuboctahedra, corners with fourteen equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with two equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with four equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Ca(1)Ca2Mg10 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Ca(1), two equivalent Mg(1), and six equivalent Mg(2) atoms to form distorted MgCa4Mg8 cuboctahedra that share corners with four equivalent Ca(1)Ca2Mg10 cuboctahedra, corners with fourteen equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with two equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with four equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Mg(1)Ca4Mg8 cuboctahedra, faces with six equivalent Ca(1)Ca2Mg10 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded to three equivalent Ca(1), three equivalent Mg(1), and six equivalent Mg(2) atoms to form distorted MgCa3Mg9 cuboctahedra that share corners with eighteen equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Ca(1)Ca2Mg10 cuboctahedra, edges with six equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Mg(1)Ca4Mg8 cuboctahedra, faces with six equivalent Ca(1)Ca2Mg10 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with eight equivalent Mg(2)Ca3Mg9 cuboctahedra. is represented by the CIF card [CIF]
data_CaMg3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.462
_cell_length_b   6.462
_cell_length_c   6.462
_cell_angle_alpha   149.791
_cell_angle_beta   126.328
_cell_angle_gamma   62.831
_symmetry_Int_Tables_number   1
_cell_volume   108.360
_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  0.337  0.000  0.337  1.0
  Mg  Mg1  1  0.831  0.500  0.331  1.0
  Mg  Mg2  1  0.244  0.245  0.999  1.0
  Mg  Mg3  1  0.754  0.755  0.999  1.0
[/CIF]
.