Al2SiO5 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form AlO6 octahedra that share corners with four equivalent Al(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. In the second Al site, Al(2) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form AlO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra and corners with three equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-63°. Si(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra and corners with three equivalent Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-55°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Al(1), one Al(2), and one Si(1) atom. In the second O site, O(2) is bonded in a linear geometry to one Al(2) and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms.
Al2SiO5 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form AlO6 octahedra that share corners with four equivalent Al(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. Both Al(1)-O(1) bond lengths are 1.95 Å. Both Al(1)-O(3) bond lengths are 1.91 Å. Both Al(1)-O(4) bond lengths are 1.87 Å. In the second Al site, Al(2) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form AlO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra and corners with three equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-63°. The Al(2)-O(2) bond length is 1.71 Å. The Al(2)-O(4) bond length is 1.74 Å. Both Al(2)-O(1) bond lengths are 1.79 Å. Si(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra and corners with three equivalent Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-55°. The Si(1)-O(2) bond length is 1.58 Å. The Si(1)-O(3) bond length is 1.64 Å. Both Si(1)-O(1) bond lengths are 1.65 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Al(1), one Al(2), and one Si(1) atom. In the second O site, O(2) is bonded in a linear geometry to one Al(2) and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms.