MgSi crystallizes in the triclinic P1 space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(5), two equivalent Si(3), and two equivalent Si(4) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(1), one Si(4), one Si(6), two equivalent Si(2), and two equivalent Si(5) atoms. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one Si(2), one Si(3), one Si(5), two equivalent Si(1), and two equivalent Si(6) atoms. In the fifth Mg site, Mg(5) is bonded to one Si(2), one Si(3), and two equivalent Si(4) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Si(6)Mg4Si3 pentagonal bipyramid, corners with two equivalent Mg(5)Si4 tetrahedra, and edges with two equivalent Mg(6)Si4 tetrahedra. In the sixth Mg site, Mg(6) is bonded to one Si(4), one Si(6), and two equivalent Si(3) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Si(2)Mg4Si3 pentagonal bipyramid, corners with two equivalent Mg(6)Si4 tetrahedra, and edges with two equivalent Mg(5)Si4 tetrahedra. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(3), two equivalent Mg(4), one Si(5), and two equivalent Si(6) atoms. In the second Si site, Si(2) is bonded to one Mg(4), one Mg(5), two equivalent Mg(3), one Si(6), and two equivalent Si(5) atoms to form distorted SiMg4Si3 pentagonal bipyramids that share  a cornercorner with one Mg(6)Si4 tetrahedra, edges with two equivalent Si(2)Mg4Si3 pentagonal bipyramids, and edges with two equivalent Si(6)Mg4Si3 pentagonal bipyramids. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(4), one Mg(5), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(6), and one Si(4) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(3), one Mg(6), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(5), and one Si(3) atom. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(4), two equivalent Mg(3), one Si(1), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded to one Mg(3), one Mg(6), two equivalent Mg(4), one Si(2), and two equivalent Si(1) atoms to form distorted SiMg4Si3 pentagonal bipyramids that share  a cornercorner with one Mg(5)Si4 tetrahedra, edges with two equivalent Si(2)Mg4Si3 pentagonal bipyramids, and edges with two equivalent Si(6)Mg4Si3 pentagonal bipyramids.
MgSi crystallizes in the triclinic P1 space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. The Mg(1)-Si(1) bond length is 2.69 Å. There is one shorter (2.77 Å) and one longer (2.80 Å) Mg(1)-Si(3) bond length. There is one shorter (2.79 Å) and one longer (2.81 Å) Mg(1)-Si(4) bond length. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(5), two equivalent Si(3), and two equivalent Si(4) atoms. The Mg(2)-Si(5) bond length is 2.69 Å. There is one shorter (2.78 Å) and one longer (2.79 Å) Mg(2)-Si(3) bond length. There is one shorter (2.76 Å) and one longer (2.79 Å) Mg(2)-Si(4) bond length. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(1), one Si(4), one Si(6), two equivalent Si(2), and two equivalent Si(5) atoms. The Mg(3)-Si(1) bond length is 2.92 Å. The Mg(3)-Si(4) bond length is 2.88 Å. The Mg(3)-Si(6) bond length is 2.85 Å. There is one shorter (2.90 Å) and one longer (2.94 Å) Mg(3)-Si(2) bond length. There is one shorter (2.92 Å) and one longer (3.27 Å) Mg(3)-Si(5) bond length. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one Si(2), one Si(3), one Si(5), two equivalent Si(1), and two equivalent Si(6) atoms. The Mg(4)-Si(2) bond length is 2.82 Å. The Mg(4)-Si(3) bond length is 2.87 Å. The Mg(4)-Si(5) bond length is 2.96 Å. There is one shorter (2.89 Å) and one longer (3.27 Å) Mg(4)-Si(1) bond length. There is one shorter (2.90 Å) and one longer (2.98 Å) Mg(4)-Si(6) bond length. In the fifth Mg site, Mg(5) is bonded to one Si(2), one Si(3), and two equivalent Si(4) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Si(6)Mg4Si3 pentagonal bipyramid, corners with two equivalent Mg(5)Si4 tetrahedra, and edges with two equivalent Mg(6)Si4 tetrahedra. The Mg(5)-Si(2) bond length is 2.74 Å. The Mg(5)-Si(3) bond length is 2.80 Å. There is one shorter (2.68 Å) and one longer (2.71 Å) Mg(5)-Si(4) bond length. In the sixth Mg site, Mg(6) is bonded to one Si(4), one Si(6), and two equivalent Si(3) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Si(2)Mg4Si3 pentagonal bipyramid, corners with two equivalent Mg(6)Si4 tetrahedra, and edges with two equivalent Mg(5)Si4 tetrahedra. The Mg(6)-Si(4) bond length is 2.77 Å. The Mg(6)-Si(6) bond length is 2.74 Å. There is one shorter (2.67 Å) and one longer (2.69 Å) Mg(6)-Si(3) bond length. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(3), two equivalent Mg(4), one Si(5), and two equivalent Si(6) atoms. The Si(1)-Si(5) bond length is 2.45 Å. There is one shorter (2.40 Å) and one longer (2.59 Å) Si(1)-Si(6) bond length. In the second Si site, Si(2) is bonded to one Mg(4), one Mg(5), two equivalent Mg(3), one Si(6), and two equivalent Si(5) atoms to form distorted SiMg4Si3 pentagonal bipyramids that share  a cornercorner with one Mg(6)Si4 tetrahedra, edges with two equivalent Si(2)Mg4Si3 pentagonal bipyramids, and edges with two equivalent Si(6)Mg4Si3 pentagonal bipyramids. The Si(2)-Si(6) bond length is 2.53 Å. There is one shorter (2.40 Å) and one longer (2.59 Å) Si(2)-Si(5) bond length. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(4), one Mg(5), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(6), and one Si(4) atom. The Si(3)-Si(4) bond length is 2.45 Å. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(3), one Mg(6), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(5), and one Si(3) atom. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(4), two equivalent Mg(3), one Si(1), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded to one Mg(3), one Mg(6), two equivalent Mg(4), one Si(2), and two equivalent Si(1) atoms to form distorted SiMg4Si3 pentagonal bipyramids that share  a cornercorner with one Mg(5)Si4 tetrahedra, edges with two equivalent Si(2)Mg4Si3 pentagonal bipyramids, and edges with two equivalent Si(6)Mg4Si3 pentagonal bipyramids.