Mg3Fe4O7 is Caswellsilverite-like structured and crystallizes in the orthorhombic Imm2 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent 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 Mg(2)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra,  an edgeedge with one Mg(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and edges with five equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. In the second Mg site, Mg(2) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with eight equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, edges with three equivalent Fe(1)O6 octahedra, edges with four equivalent Mg(1)O6 octahedra, and edges with four equivalent Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-2°. In the second Fe site, Fe(2) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra,  an edgeedge with one Fe(1)O6 octahedra, edges with five equivalent Mg(1)O6 octahedra, and edges with six equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(2) and four equivalent Fe(1) atoms to form OMg2Fe4 octahedra that share corners with two equivalent O(1)Mg2Fe4 octahedra, corners with four equivalent O(2)Mg2Fe4 octahedra, edges with two equivalent O(1)Mg2Fe4 octahedra, edges with two equivalent O(2)Mg2Fe4 octahedra, and edges with eight equivalent O(4)Mg4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second O site, O(2) is bonded to two equivalent Mg(1), two equivalent Fe(1), and two equivalent Fe(2) atoms to form OMg2Fe4 octahedra that share corners with two equivalent O(1)Mg2Fe4 octahedra, corners with two equivalent O(2)Mg2Fe4 octahedra, corners with two equivalent O(3)Mg2Fe4 octahedra,  an edgeedge with one O(1)Mg2Fe4 octahedra, edges with two equivalent O(2)Mg2Fe4 octahedra, edges with four equivalent O(4)Mg4Fe2 octahedra, and edges with five equivalent O(3)Mg2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. In the third O site, O(3) is bonded to two equivalent Mg(1) and four equivalent Fe(2) atoms to form OMg2Fe4 octahedra that share corners with two equivalent O(2)Mg2Fe4 octahedra, corners with two equivalent O(3)Mg2Fe4 octahedra, corners with two equivalent O(4)Mg4Fe2 octahedra,  an edgeedge with one O(4)Mg4Fe2 octahedra, edges with five equivalent O(2)Mg2Fe4 octahedra, and edges with six equivalent O(3)Mg2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. In the fourth O site, O(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), and two equivalent Fe(1) atoms to form OMg4Fe2 octahedra that share corners with two equivalent O(3)Mg2Fe4 octahedra, corners with four equivalent O(4)Mg4Fe2 octahedra,  an edgeedge with one O(3)Mg2Fe4 octahedra, edges with three equivalent O(4)Mg4Fe2 octahedra, edges with four equivalent O(1)Mg2Fe4 octahedra, and edges with four equivalent O(2)Mg2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 0-1°.
Mg3Fe4O7 is Caswellsilverite-like structured and crystallizes in the orthorhombic Imm2 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent 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 Mg(2)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra,  an edgeedge with one Mg(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and edges with five equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. Both Mg(1)-O(2) bond lengths are 2.18 Å. There is one shorter (2.10 Å) and one longer (2.14 Å) Mg(1)-O(3) bond length. There is one shorter (2.14 Å) and one longer (2.15 Å) Mg(1)-O(4) bond length. In the second Mg site, Mg(2) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with eight equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. Both Mg(2)-O(1) bond lengths are 2.17 Å. There are two shorter (2.16 Å) and two longer (2.17 Å) Mg(2)-O(4) bond lengths. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, edges with three equivalent Fe(1)O6 octahedra, edges with four equivalent Mg(1)O6 octahedra, and edges with four equivalent Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-2°. There is one shorter (2.15 Å) and one longer (2.21 Å) Fe(1)-O(1) bond length. There is one shorter (2.14 Å) and one longer (2.22 Å) Fe(1)-O(2) bond length. Both Fe(1)-O(4) bond lengths are 2.17 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra,  an edgeedge with one Fe(1)O6 octahedra, edges with five equivalent Mg(1)O6 octahedra, and edges with six equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. There is one shorter (2.15 Å) and one longer (2.19 Å) Fe(2)-O(2) bond length. There are a spread of Fe(2)-O(3) bond distances ranging from 2.14-2.24 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(2) and four equivalent Fe(1) atoms to form OMg2Fe4 octahedra that share corners with two equivalent O(1)Mg2Fe4 octahedra, corners with four equivalent O(2)Mg2Fe4 octahedra, edges with two equivalent O(1)Mg2Fe4 octahedra, edges with two equivalent O(2)Mg2Fe4 octahedra, and edges with eight equivalent O(4)Mg4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second O site, O(2) is bonded to two equivalent Mg(1), two equivalent Fe(1), and two equivalent Fe(2) atoms to form OMg2Fe4 octahedra that share corners with two equivalent O(1)Mg2Fe4 octahedra, corners with two equivalent O(2)Mg2Fe4 octahedra, corners with two equivalent O(3)Mg2Fe4 octahedra,  an edgeedge with one O(1)Mg2Fe4 octahedra, edges with two equivalent O(2)Mg2Fe4 octahedra, edges with four equivalent O(4)Mg4Fe2 octahedra, and edges with five equivalent O(3)Mg2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. In the third O site, O(3) is bonded to two equivalent Mg(1) and four equivalent Fe(2) atoms to form OMg2Fe4 octahedra that share corners with two equivalent O(2)Mg2Fe4 octahedra, corners with two equivalent O(3)Mg2Fe4 octahedra, corners with two equivalent O(4)Mg4Fe2 octahedra,  an edgeedge with one O(4)Mg4Fe2 octahedra, edges with five equivalent O(2)Mg2Fe4 octahedra, and edges with six equivalent O(3)Mg2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. In the fourth O site, O(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), and two equivalent Fe(1) atoms to form OMg4Fe2 octahedra that share corners with two equivalent O(3)Mg2Fe4 octahedra, corners with four equivalent O(4)Mg4Fe2 octahedra,  an edgeedge with one O(3)Mg2Fe4 octahedra, edges with three equivalent O(4)Mg4Fe2 octahedra, edges with four equivalent O(1)Mg2Fe4 octahedra, and edges with four equivalent O(2)Mg2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 0-1°.