Gd2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Gd sites. In the first Gd site, Gd(1) is bonded in a 9-coordinate geometry to one O(5), two equivalent O(1), three equivalent O(2), and three equivalent O(4) atoms. In the second Gd site, Gd(2) is bonded to one O(1), three equivalent O(3), and three equivalent O(5) atoms to form distorted GdO7 hexagonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with six equivalent Gd(2)O7 hexagonal pyramids, and  an edgeedge with one Si(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Gd(2)O7 hexagonal pyramids and  an edgeedge with one Gd(2)O7 hexagonal pyramid. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Gd(2), two equivalent Gd(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to three equivalent Gd(1) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Gd(2) and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to three equivalent Gd(1) and one Si(1) atom. In the fifth O site, O(5) is bonded to one Gd(1) and three equivalent Gd(2) atoms to form a mixture of corner and edge-sharing OGd4 tetrahedra.
Gd2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Gd sites. In the first Gd site, Gd(1) is bonded in a 9-coordinate geometry to one O(5), two equivalent O(1), three equivalent O(2), and three equivalent O(4) atoms. The Gd(1)-O(5) bond length is 2.36 Å. There is one shorter (2.30 Å) and one longer (2.51 Å) Gd(1)-O(1) bond length. There are a spread of Gd(1)-O(2) bond distances ranging from 2.34-2.58 Å. There are a spread of Gd(1)-O(4) bond distances ranging from 2.43-2.76 Å. In the second Gd site, Gd(2) is bonded to one O(1), three equivalent O(3), and three equivalent O(5) atoms to form distorted GdO7 hexagonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with six equivalent Gd(2)O7 hexagonal pyramids, and  an edgeedge with one Si(1)O4 tetrahedra. The Gd(2)-O(1) bond length is 2.38 Å. There are a spread of Gd(2)-O(3) bond distances ranging from 2.37-2.55 Å. There are a spread of Gd(2)-O(5) bond distances ranging from 2.29-2.32 Å. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Gd(2)O7 hexagonal pyramids and  an edgeedge with one Gd(2)O7 hexagonal pyramid. The Si(1)-O(1) bond length is 1.65 Å. The Si(1)-O(2) bond length is 1.62 Å. The Si(1)-O(3) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.60 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Gd(2), two equivalent Gd(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to three equivalent Gd(1) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Gd(2) and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to three equivalent Gd(1) and one Si(1) atom. In the fifth O site, O(5) is bonded to one Gd(1) and three equivalent Gd(2) atoms to form a mixture of corner and edge-sharing OGd4 tetrahedra.