Mg4Sc3(SiO3)8 crystallizes in the monoclinic P2 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form distorted MgO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Sc(1)O6 octahedra, edges with two equivalent Sc(2)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. In the second Mg site, Mg(2) is bonded to two equivalent O(11), two equivalent O(7), and two equivalent O(9) atoms to form distorted MgO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra, edges with two equivalent Sc(3)O6 octahedra, and edges with two equivalent Si(3)O4 tetrahedra. In the third Mg site, Mg(3) is bonded to two equivalent O(10), two equivalent O(11), and two equivalent O(12) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra, and edges with two equivalent Sc(3)O6 octahedra. In the fourth Mg site, Mg(4) is bonded to two equivalent O(10), two equivalent O(12), and two equivalent O(8) atoms to form distorted MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra,  an edgeedge with one Sc(3)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Si(4)O4 tetrahedra. There are three inequivalent Sc sites. In the first Sc site, Sc(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted ScO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Sc(2)O6 octahedra. In the second Sc site, Sc(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form ScO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Sc(1)O6 octahedra. In the third Sc site, Sc(3) is bonded to two equivalent O(11), two equivalent O(12), and two equivalent O(9) atoms to form ScO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with two equivalent Mg(3)O6 octahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(12), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Mg(4)O6 octahedra,  a cornercorner with one Sc(2)O6 octahedra,  a cornercorner with one Sc(3)O6 octahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-63°. In the second Si site, Si(2) is bonded to one O(11), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Sc(1)O6 octahedra,  a cornercorner with one Sc(3)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-63°. In the third Si site, Si(3) is bonded to one O(1), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(4)O6 octahedra,  a cornercorner with one Sc(1)O6 octahedra,  a cornercorner with one Sc(2)O6 octahedra,  a cornercorner with one Sc(3)O6 octahedra, corners with two equivalent Si(4)O4 tetrahedra, and  an edgeedge with one Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-57°. In the fourth Si site, Si(4) is bonded to one O(10), one O(2), one O(7), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Sc(1)O6 octahedra,  a cornercorner with one Sc(2)O6 octahedra, corners with two equivalent Si(3)O4 tetrahedra, and  an edgeedge with one Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 33-63°. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Sc(1), one Sc(2), and one Si(3) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Sc(1), one Sc(2), and one Si(4) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Sc(1) and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Mg(1), one Sc(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(2), one Si(3), and one Si(4) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Mg(4), one Si(3), and one Si(4) atom. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Mg(2), one Sc(3), and one Si(3) atom. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Mg(3), one Mg(4), and one Si(4) atom. In the eleventh O site, O(11) is bonded in a distorted rectangular see-saw-like geometry to one Mg(2), one Mg(3), one Sc(3), and one Si(2) atom. In the twelfth O site, O(12) is bonded in a distorted rectangular see-saw-like geometry to one Mg(3), one Mg(4), one Sc(3), and one Si(1) atom.
Mg4Sc3(SiO3)8 crystallizes in the monoclinic P2 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form distorted MgO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Sc(1)O6 octahedra, edges with two equivalent Sc(2)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. Both Mg(1)-O(2) bond lengths are 2.12 Å. Both Mg(1)-O(4) bond lengths are 2.06 Å. Both Mg(1)-O(6) bond lengths are 2.36 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(11), two equivalent O(7), and two equivalent O(9) atoms to form distorted MgO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra, edges with two equivalent Sc(3)O6 octahedra, and edges with two equivalent Si(3)O4 tetrahedra. Both Mg(2)-O(11) bond lengths are 2.09 Å. Both Mg(2)-O(7) bond lengths are 2.42 Å. Both Mg(2)-O(9) bond lengths are 2.05 Å. In the third Mg site, Mg(3) is bonded to two equivalent O(10), two equivalent O(11), and two equivalent O(12) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra, and edges with two equivalent Sc(3)O6 octahedra. Both Mg(3)-O(10) bond lengths are 2.02 Å. Both Mg(3)-O(11) bond lengths are 2.23 Å. Both Mg(3)-O(12) bond lengths are 2.09 Å. In the fourth Mg site, Mg(4) is bonded to two equivalent O(10), two equivalent O(12), and two equivalent O(8) atoms to form distorted MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra,  an edgeedge with one Sc(3)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Si(4)O4 tetrahedra. Both Mg(4)-O(10) bond lengths are 2.04 Å. Both Mg(4)-O(12) bond lengths are 2.11 Å. Both Mg(4)-O(8) bond lengths are 2.42 Å. There are three inequivalent Sc sites. In the first Sc site, Sc(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted ScO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Sc(2)O6 octahedra. Both Sc(1)-O(1) bond lengths are 2.13 Å. Both Sc(1)-O(2) bond lengths are 2.43 Å. Both Sc(1)-O(3) bond lengths are 1.99 Å. In the second Sc site, Sc(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form ScO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, corners with two equivalent Si(4)O4 tetrahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Sc(1)O6 octahedra. Both Sc(2)-O(1) bond lengths are 2.14 Å. Both Sc(2)-O(2) bond lengths are 2.19 Å. Both Sc(2)-O(4) bond lengths are 2.13 Å. In the third Sc site, Sc(3) is bonded to two equivalent O(11), two equivalent O(12), and two equivalent O(9) atoms to form ScO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with two equivalent Mg(3)O6 octahedra. Both Sc(3)-O(11) bond lengths are 2.15 Å. Both Sc(3)-O(12) bond lengths are 2.28 Å. Both Sc(3)-O(9) bond lengths are 2.09 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(12), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Mg(4)O6 octahedra,  a cornercorner with one Sc(2)O6 octahedra,  a cornercorner with one Sc(3)O6 octahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-63°. The Si(1)-O(12) bond length is 1.66 Å. The Si(1)-O(4) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.64 Å. The Si(1)-O(6) bond length is 1.68 Å. In the second Si site, Si(2) is bonded to one O(11), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Sc(1)O6 octahedra,  a cornercorner with one Sc(3)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-63°. The Si(2)-O(11) bond length is 1.66 Å. The Si(2)-O(3) bond length is 1.59 Å. The Si(2)-O(5) bond length is 1.65 Å. The Si(2)-O(6) bond length is 1.68 Å. In the third Si site, Si(3) is bonded to one O(1), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(4)O6 octahedra,  a cornercorner with one Sc(1)O6 octahedra,  a cornercorner with one Sc(2)O6 octahedra,  a cornercorner with one Sc(3)O6 octahedra, corners with two equivalent Si(4)O4 tetrahedra, and  an edgeedge with one Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-57°. The Si(3)-O(1) bond length is 1.61 Å. The Si(3)-O(7) bond length is 1.69 Å. The Si(3)-O(8) bond length is 1.67 Å. The Si(3)-O(9) bond length is 1.62 Å. In the fourth Si site, Si(4) is bonded to one O(10), one O(2), one O(7), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one Mg(2)O6 octahedra,  a cornercorner with one Mg(3)O6 octahedra,  a cornercorner with one Sc(1)O6 octahedra,  a cornercorner with one Sc(2)O6 octahedra, corners with two equivalent Si(3)O4 tetrahedra, and  an edgeedge with one Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 33-63°. The Si(4)-O(10) bond length is 1.61 Å. The Si(4)-O(2) bond length is 1.64 Å. The Si(4)-O(7) bond length is 1.66 Å. The Si(4)-O(8) bond length is 1.69 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Sc(1), one Sc(2), and one Si(3) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Sc(1), one Sc(2), and one Si(4) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Sc(1) and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Mg(1), one Sc(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(2), one Si(3), and one Si(4) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Mg(4), one Si(3), and one Si(4) atom. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Mg(2), one Sc(3), and one Si(3) atom. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Mg(3), one Mg(4), and one Si(4) atom. In the eleventh O site, O(11) is bonded in a distorted rectangular see-saw-like geometry to one Mg(2), one Mg(3), one Sc(3), and one Si(2) atom. In the twelfth O site, O(12) is bonded in a distorted rectangular see-saw-like geometry to one Mg(3), one Mg(4), one Sc(3), and one Si(1) atom.