Fe7(SiO3)8 crystallizes in the monoclinic C2/m space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(5) and two equivalent O(7) atoms. In the second Fe site, Fe(2) is bonded to two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(6) atoms to form FeO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(4)O6 octahedra. In the fourth Fe site, Fe(4) is bonded to two equivalent O(3), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(4)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one Fe(3)O6 octahedra,  a cornercorner with one Fe(4)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-60°. In the second Si site, Si(2) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(4)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-60°. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the second O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3) and two equivalent Fe(4) atoms. In the third O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fourth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(2), and one Si(2) atom. In the fifth O site, O(6) is bonded to one Fe(2), one Fe(3), one Fe(4), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OFe3Si trigonal pyramids. In the sixth O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Fe(4), and one Si(2) atom. In the seventh O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom.
Fe7(SiO3)8 crystallizes in the monoclinic C2/m space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(5) and two equivalent O(7) atoms. Both Fe(1)-O(5) bond lengths are 2.03 Å. Both Fe(1)-O(7) bond lengths are 2.17 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. Both Fe(2)-O(5) bond lengths are 2.09 Å. Both Fe(2)-O(6) bond lengths are 2.22 Å. Both Fe(2)-O(7) bond lengths are 2.18 Å. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(6) atoms to form FeO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(4)O6 octahedra. Both Fe(3)-O(3) bond lengths are 1.95 Å. All Fe(3)-O(6) bond lengths are 2.11 Å. In the fourth Fe site, Fe(4) is bonded to two equivalent O(3), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(4)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. Both Fe(4)-O(3) bond lengths are 2.01 Å. Both Fe(4)-O(6) bond lengths are 2.14 Å. Both Fe(4)-O(7) bond lengths are 2.22 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one Fe(3)O6 octahedra,  a cornercorner with one Fe(4)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-60°. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(2) bond length is 1.62 Å. The Si(1)-O(4) bond length is 1.64 Å. The Si(1)-O(6) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(4)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-60°. The Si(2)-O(1) bond length is 1.66 Å. The Si(2)-O(4) bond length is 1.65 Å. The Si(2)-O(5) bond length is 1.63 Å. The Si(2)-O(7) bond length is 1.65 Å. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the second O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3) and two equivalent Fe(4) atoms. In the third O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fourth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(2), and one Si(2) atom. In the fifth O site, O(6) is bonded to one Fe(2), one Fe(3), one Fe(4), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OFe3Si trigonal pyramids. In the sixth O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Fe(4), and one Si(2) atom. In the seventh O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom.