Fe8SiO12 crystallizes in the monoclinic P2_1/m space group. There are seven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(8) atoms to form FeO6 octahedra that share corners with two equivalent Fe(3)O4 tetrahedra, corners with two equivalent Fe(4)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(5)O6 octahedra, and edges with two equivalent Fe(7)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(2), one O(3), one O(5), one O(9), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one Fe(4)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Fe(3)O4 tetrahedra,  an edgeedge with one Fe(5)O6 octahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(6)O6 octahedra, and edges with three equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles are 15°. In the third Fe site, Fe(3) is bonded to one O(5), one O(9), and two equivalent O(1) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-59°. In the fourth Fe site, Fe(4) is bonded to one O(4), one O(7), and two equivalent O(2) atoms to form FeO4 tetrahedra that share  a cornercorner with one Fe(5)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(7)O6 octahedra, corners with three equivalent Fe(6)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-68°. In the fifth Fe site, Fe(5) is bonded to one O(4), one O(5), two equivalent O(1), and two equivalent O(3) atoms to form FeO6 octahedra that share  a cornercorner with one Fe(4)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Fe(3)O4 tetrahedra,  an edgeedge with one Fe(6)O6 octahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(2)O6 octahedra. In the sixth Fe site, Fe(6) is bonded to one O(6), one O(7), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with three equivalent Fe(4)O4 tetrahedra, corners with three equivalent Si(1)O4 tetrahedra,  an edgeedge with one Fe(5)O6 octahedra,  an edgeedge with one Fe(7)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. In the seventh Fe site, Fe(7) is bonded to one O(8), one O(9), two equivalent O(1), and two equivalent O(2) atoms to form FeO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Fe(4)O4 tetrahedra, corners with three equivalent Fe(3)O4 tetrahedra,  an edgeedge with one Fe(5)O6 octahedra,  an edgeedge with one Fe(6)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(2)O6 octahedra. Si(1) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form SiO4 tetrahedra that share  a cornercorner with one Fe(7)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(5)O6 octahedra, corners with three equivalent Fe(6)O6 octahedra, and  a cornercorner with one Fe(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-57°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(3), one Fe(5), and one Fe(7) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Fe(2), one Fe(4), one Fe(6), and one Fe(7) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Fe(2), one Fe(5), one Fe(6), and one Si(1) atom. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Fe(4), one Fe(5), and two equivalent Fe(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Fe(3), one Fe(5), and two equivalent Fe(2) atoms. In the sixth O site, O(6) is bonded to one Fe(6) and four equivalent Fe(2) atoms to form edge-sharing OFe5 square pyramids. In the seventh O site, O(7) is bonded in a trigonal planar geometry to one Fe(4), one Fe(6), and one Si(1) atom. In the eighth O site, O(8) is bonded in a distorted rectangular see-saw-like geometry to one Fe(7), two equivalent Fe(1), and one Si(1) atom. In the ninth O site, O(9) is bonded in a rectangular see-saw-like geometry to one Fe(3), one Fe(7), and two equivalent Fe(2) atoms.
Fe8SiO12 crystallizes in the monoclinic P2_1/m space group. There are seven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(8) atoms to form FeO6 octahedra that share corners with two equivalent Fe(3)O4 tetrahedra, corners with two equivalent Fe(4)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(5)O6 octahedra, and edges with two equivalent Fe(7)O6 octahedra. Both Fe(1)-O(1) bond lengths are 2.12 Å. Both Fe(1)-O(4) bond lengths are 2.11 Å. Both Fe(1)-O(8) bond lengths are 2.26 Å. In the second Fe site, Fe(2) is bonded to one O(2), one O(3), one O(5), one O(9), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one Fe(4)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Fe(3)O4 tetrahedra,  an edgeedge with one Fe(5)O6 octahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(6)O6 octahedra, and edges with three equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles are 15°. The Fe(2)-O(2) bond length is 2.08 Å. The Fe(2)-O(3) bond length is 2.13 Å. The Fe(2)-O(5) bond length is 2.12 Å. The Fe(2)-O(9) bond length is 2.08 Å. Both Fe(2)-O(6) bond lengths are 2.13 Å. In the third Fe site, Fe(3) is bonded to one O(5), one O(9), and two equivalent O(1) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-59°. The Fe(3)-O(5) bond length is 1.93 Å. The Fe(3)-O(9) bond length is 1.95 Å. Both Fe(3)-O(1) bond lengths are 1.93 Å. In the fourth Fe site, Fe(4) is bonded to one O(4), one O(7), and two equivalent O(2) atoms to form FeO4 tetrahedra that share  a cornercorner with one Fe(5)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(7)O6 octahedra, corners with three equivalent Fe(6)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-68°. The Fe(4)-O(4) bond length is 1.90 Å. The Fe(4)-O(7) bond length is 1.97 Å. Both Fe(4)-O(2) bond lengths are 1.91 Å. In the fifth Fe site, Fe(5) is bonded to one O(4), one O(5), two equivalent O(1), and two equivalent O(3) atoms to form FeO6 octahedra that share  a cornercorner with one Fe(4)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Fe(3)O4 tetrahedra,  an edgeedge with one Fe(6)O6 octahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(2)O6 octahedra. The Fe(5)-O(4) bond length is 2.07 Å. The Fe(5)-O(5) bond length is 2.07 Å. Both Fe(5)-O(1) bond lengths are 2.16 Å. Both Fe(5)-O(3) bond lengths are 2.23 Å. In the sixth Fe site, Fe(6) is bonded to one O(6), one O(7), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with three equivalent Fe(4)O4 tetrahedra, corners with three equivalent Si(1)O4 tetrahedra,  an edgeedge with one Fe(5)O6 octahedra,  an edgeedge with one Fe(7)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. The Fe(6)-O(6) bond length is 2.16 Å. The Fe(6)-O(7) bond length is 2.09 Å. Both Fe(6)-O(2) bond lengths are 2.15 Å. Both Fe(6)-O(3) bond lengths are 2.26 Å. In the seventh Fe site, Fe(7) is bonded to one O(8), one O(9), two equivalent O(1), and two equivalent O(2) atoms to form FeO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Fe(4)O4 tetrahedra, corners with three equivalent Fe(3)O4 tetrahedra,  an edgeedge with one Fe(5)O6 octahedra,  an edgeedge with one Fe(6)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(2)O6 octahedra. The Fe(7)-O(8) bond length is 2.16 Å. The Fe(7)-O(9) bond length is 2.09 Å. Both Fe(7)-O(1) bond lengths are 2.01 Å. Both Fe(7)-O(2) bond lengths are 2.05 Å. Si(1) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form SiO4 tetrahedra that share  a cornercorner with one Fe(7)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(5)O6 octahedra, corners with three equivalent Fe(6)O6 octahedra, and  a cornercorner with one Fe(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-57°. The Si(1)-O(7) bond length is 1.67 Å. The Si(1)-O(8) bond length is 1.66 Å. Both Si(1)-O(3) bond lengths are 1.67 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(3), one Fe(5), and one Fe(7) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Fe(2), one Fe(4), one Fe(6), and one Fe(7) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Fe(2), one Fe(5), one Fe(6), and one Si(1) atom. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Fe(4), one Fe(5), and two equivalent Fe(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Fe(3), one Fe(5), and two equivalent Fe(2) atoms. In the sixth O site, O(6) is bonded to one Fe(6) and four equivalent Fe(2) atoms to form edge-sharing OFe5 square pyramids. In the seventh O site, O(7) is bonded in a trigonal planar geometry to one Fe(4), one Fe(6), and one Si(1) atom. In the eighth O site, O(8) is bonded in a distorted rectangular see-saw-like geometry to one Fe(7), two equivalent Fe(1), and one Si(1) atom. In the ninth O site, O(9) is bonded in a rectangular see-saw-like geometry to one Fe(3), one Fe(7), and two equivalent Fe(2) atoms.