MgSi2O5 crystallizes in the orthorhombic Pbam space group. Mg(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), and four equivalent O(1) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted SiO5 square pyramids that share corners with four equivalent Si(2)O6 octahedra and  an edgeedge with one Si(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-51°. In the second Si site, Si(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form SiO6 octahedra that share corners with four equivalent Si(1)O5 square pyramids and edges with two equivalent Si(2)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Mg(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded to two equivalent Mg(1) and two equivalent Si(1) atoms to form a mixture of distorted edge and corner-sharing OMg2Si2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Mg(1) and two equivalent Si(2) atoms to form a mixture of distorted edge and corner-sharing OMg2Si2 trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Si(1) and two equivalent Si(2) atoms.
MgSi2O5 crystallizes in the orthorhombic Pbam space group. Mg(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), and four equivalent O(1) atoms. Both Mg(1)-O(2) bond lengths are 2.22 Å. There is one shorter (2.13 Å) and one longer (2.22 Å) Mg(1)-O(3) bond length. There are two shorter (2.21 Å) and two longer (2.50 Å) Mg(1)-O(1) bond lengths. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted SiO5 square pyramids that share corners with four equivalent Si(2)O6 octahedra and  an edgeedge with one Si(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-51°. The Si(1)-O(4) bond length is 1.70 Å. Both Si(1)-O(1) bond lengths are 1.72 Å. Both Si(1)-O(2) bond lengths are 1.78 Å. In the second Si site, Si(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form SiO6 octahedra that share corners with four equivalent Si(1)O5 square pyramids and edges with two equivalent Si(2)O6 octahedra. Both Si(2)-O(1) bond lengths are 1.77 Å. Both Si(2)-O(3) bond lengths are 1.77 Å. Both Si(2)-O(4) bond lengths are 1.84 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Mg(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded to two equivalent Mg(1) and two equivalent Si(1) atoms to form a mixture of distorted edge and corner-sharing OMg2Si2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Mg(1) and two equivalent Si(2) atoms to form a mixture of distorted edge and corner-sharing OMg2Si2 trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Si(1) and two equivalent Si(2) atoms.