Al2SiO5 crystallizes in the orthorhombic Cmcm space group. Al(1) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(1) atoms. Si(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing SiO6 octahedra. The corner-sharing octahedral tilt angles are 32°. There are three inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Al(1) and one Si(1) atom to form distorted OAl3Si trigonal pyramids that share  a cornercorner with one O(3)Al2Si2 tetrahedra, corners with three equivalent O(1)Al3Si trigonal pyramids, edges with two equivalent O(3)Al2Si2 tetrahedra, and edges with two equivalent O(1)Al3Si trigonal pyramids. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Al(1) and one Si(1) atom. In the third O site, O(3) is bonded to two equivalent Al(1) and two equivalent Si(1) atoms to form distorted OAl2Si2 tetrahedra that share corners with two equivalent O(3)Al2Si2 tetrahedra, corners with two equivalent O(1)Al3Si trigonal pyramids, and edges with four equivalent O(1)Al3Si trigonal pyramids.
Al2SiO5 crystallizes in the orthorhombic Cmcm space group. Al(1) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(1) atoms. The Al(1)-O(3) bond length is 2.04 Å. There is one shorter (1.83 Å) and one longer (1.85 Å) Al(1)-O(2) bond length. There are two shorter (1.86 Å) and one longer (2.19 Å) Al(1)-O(1) bond length. Si(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing SiO6 octahedra. The corner-sharing octahedral tilt angles are 32°. Both Si(1)-O(1) bond lengths are 1.89 Å. Both Si(1)-O(2) bond lengths are 1.70 Å. Both Si(1)-O(3) bond lengths are 1.86 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Al(1) and one Si(1) atom to form distorted OAl3Si trigonal pyramids that share  a cornercorner with one O(3)Al2Si2 tetrahedra, corners with three equivalent O(1)Al3Si trigonal pyramids, edges with two equivalent O(3)Al2Si2 tetrahedra, and edges with two equivalent O(1)Al3Si trigonal pyramids. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Al(1) and one Si(1) atom. In the third O site, O(3) is bonded to two equivalent Al(1) and two equivalent Si(1) atoms to form distorted OAl2Si2 tetrahedra that share corners with two equivalent O(3)Al2Si2 tetrahedra, corners with two equivalent O(1)Al3Si trigonal pyramids, and edges with four equivalent O(1)Al3Si trigonal pyramids.