MgNb3SiO10 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(2), one O(3), one O(7), one O(8), and one O(9) atom to form distorted MgO6 octahedra that share  a cornercorner with one Nb(3)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Si(1)O6 octahedra, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles are 63°. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(8) atom to form NbO6 octahedra that share corners with three equivalent Nb(3)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra, and  an edgeedge with one Si(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-59°. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. In the third Nb site, Nb(3) is bonded to one O(1), one O(10), one O(2), one O(4), one O(8), and one O(9) atom to form NbO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, corners with four equivalent Si(1)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-63°. Si(1) is bonded to one O(1), one O(10), one O(2), one O(6), one O(7), and one O(9) atom to form SiO6 octahedra that share corners with four equivalent Nb(3)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra, and edges with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-44°. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(3), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(3), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Nb(1), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Nb(1), one Nb(2), and one Nb(3) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(2), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Nb(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a T-shaped geometry to one Mg(1), one Nb(1), and one Nb(3) atom. In the ninth O site, O(9) is bonded in a T-shaped geometry to one Mg(1), one Nb(3), and one Si(1) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Mg(1), one Nb(2), one Nb(3), and one Si(1) atom.
MgNb3SiO10 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(2), one O(3), one O(7), one O(8), and one O(9) atom to form distorted MgO6 octahedra that share  a cornercorner with one Nb(3)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Si(1)O6 octahedra, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles are 63°. The Mg(1)-O(10) bond length is 2.18 Å. The Mg(1)-O(2) bond length is 2.01 Å. The Mg(1)-O(3) bond length is 2.04 Å. The Mg(1)-O(7) bond length is 1.98 Å. The Mg(1)-O(8) bond length is 2.24 Å. The Mg(1)-O(9) bond length is 2.02 Å. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(8) atom to form NbO6 octahedra that share corners with three equivalent Nb(3)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra, and  an edgeedge with one Si(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-59°. The Nb(1)-O(1) bond length is 2.13 Å. The Nb(1)-O(3) bond length is 1.99 Å. The Nb(1)-O(4) bond length is 2.06 Å. The Nb(1)-O(5) bond length is 2.01 Å. The Nb(1)-O(6) bond length is 2.10 Å. The Nb(1)-O(8) bond length is 1.96 Å. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. The Nb(2)-O(10) bond length is 2.54 Å. The Nb(2)-O(3) bond length is 1.98 Å. The Nb(2)-O(4) bond length is 2.17 Å. The Nb(2)-O(5) bond length is 1.85 Å. The Nb(2)-O(6) bond length is 2.06 Å. The Nb(2)-O(7) bond length is 1.95 Å. In the third Nb site, Nb(3) is bonded to one O(1), one O(10), one O(2), one O(4), one O(8), and one O(9) atom to form NbO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, corners with four equivalent Si(1)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-63°. The Nb(3)-O(1) bond length is 2.07 Å. The Nb(3)-O(10) bond length is 2.25 Å. The Nb(3)-O(2) bond length is 1.89 Å. The Nb(3)-O(4) bond length is 2.06 Å. The Nb(3)-O(8) bond length is 1.97 Å. The Nb(3)-O(9) bond length is 2.05 Å. Si(1) is bonded to one O(1), one O(10), one O(2), one O(6), one O(7), and one O(9) atom to form SiO6 octahedra that share corners with four equivalent Nb(3)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra, and edges with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-44°. The Si(1)-O(1) bond length is 1.87 Å. The Si(1)-O(10) bond length is 1.75 Å. The Si(1)-O(2) bond length is 1.95 Å. The Si(1)-O(6) bond length is 1.82 Å. The Si(1)-O(7) bond length is 1.92 Å. The Si(1)-O(9) bond length is 1.73 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(3), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(3), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Nb(1), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Nb(1), one Nb(2), and one Nb(3) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(2), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Nb(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a T-shaped geometry to one Mg(1), one Nb(1), and one Nb(3) atom. In the ninth O site, O(9) is bonded in a T-shaped geometry to one Mg(1), one Nb(3), and one Si(1) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Mg(1), one Nb(2), one Nb(3), and one Si(1) atom.