Ho2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to one O(4), three equivalent O(1), and three equivalent O(3) atoms to form distorted HoO7 hexagonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with six equivalent Ho(1)O7 hexagonal pyramids, and  an edgeedge with one Si(1)O4 tetrahedra. In the second Ho site, Ho(2) is bonded in a 8-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(4), and three equivalent O(5) atoms. Si(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with two equivalent Ho(1)O7 hexagonal pyramids and  an edgeedge with one Ho(1)O7 hexagonal pyramid. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Ho(2) and three equivalent Ho(1) atoms to form a mixture of corner and edge-sharing OHo4 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ho(2) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Ho(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ho(1), two equivalent Ho(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to three equivalent Ho(2) and one Si(1) atom.
Ho2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to one O(4), three equivalent O(1), and three equivalent O(3) atoms to form distorted HoO7 hexagonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with six equivalent Ho(1)O7 hexagonal pyramids, and  an edgeedge with one Si(1)O4 tetrahedra. The Ho(1)-O(4) bond length is 2.31 Å. There are a spread of Ho(1)-O(1) bond distances ranging from 2.21-2.28 Å. There are a spread of Ho(1)-O(3) bond distances ranging from 2.34-2.52 Å. In the second Ho site, Ho(2) is bonded in a 8-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(4), and three equivalent O(5) atoms. The Ho(2)-O(1) bond length is 2.26 Å. There is one shorter (2.32 Å) and one longer (2.43 Å) Ho(2)-O(2) bond length. There is one shorter (2.23 Å) and one longer (2.46 Å) Ho(2)-O(4) bond length. There are a spread of Ho(2)-O(5) bond distances ranging from 2.29-2.71 Å. Si(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with two equivalent Ho(1)O7 hexagonal pyramids and  an edgeedge with one Ho(1)O7 hexagonal pyramid. The Si(1)-O(2) bond length is 1.60 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.65 Å. The Si(1)-O(5) bond length is 1.62 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Ho(2) and three equivalent Ho(1) atoms to form a mixture of corner and edge-sharing OHo4 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ho(2) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Ho(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ho(1), two equivalent Ho(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to three equivalent Ho(2) and one Si(1) atom.