Mg2Fe3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Fe(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra, and edges with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. In the second Mg site, Mg(2) is bonded to one O(4) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and corners with nine equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-63°. Fe(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mg(1) and two equivalent Fe(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and two equivalent Fe(1) atoms to form distorted OMg2Fe2 tetrahedra that share corners with two equivalent O(2)Mg2Fe2 tetrahedra,  a cornercorner with one O(4)MgFe3 trigonal pyramid, edges with two equivalent O(2)Mg2Fe2 tetrahedra, and  an edgeedge with one O(4)MgFe3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded to one Mg(2) and three equivalent Fe(1) atoms to form a mixture of distorted corner and edge-sharing OMgFe3 trigonal pyramids.
Mg2Fe3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Fe(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra, and edges with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. All Mg(1)-O(1) bond lengths are 2.09 Å. All Mg(1)-O(2) bond lengths are 2.13 Å. In the second Mg site, Mg(2) is bonded to one O(4) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and corners with nine equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-63°. The Mg(2)-O(4) bond length is 2.00 Å. All Mg(2)-O(2) bond lengths are 1.97 Å. Fe(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. The Fe(1)-O(3) bond length is 1.99 Å. The Fe(1)-O(4) bond length is 2.05 Å. Both Fe(1)-O(1) bond lengths are 1.93 Å. Both Fe(1)-O(2) bond lengths are 2.00 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mg(1) and two equivalent Fe(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and two equivalent Fe(1) atoms to form distorted OMg2Fe2 tetrahedra that share corners with two equivalent O(2)Mg2Fe2 tetrahedra,  a cornercorner with one O(4)MgFe3 trigonal pyramid, edges with two equivalent O(2)Mg2Fe2 tetrahedra, and  an edgeedge with one O(4)MgFe3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded to one Mg(2) and three equivalent Fe(1) atoms to form a mixture of distorted corner and edge-sharing OMgFe3 trigonal pyramids.