Al3(SiO5)2 crystallizes in the triclinic P-1 space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(2) atoms to form AlO6 octahedra that share corners with five equivalent Si(1)O4 tetrahedra,  an edgeedge with one Al(2)O6 octahedra, and edges with two equivalent Al(1)O6 octahedra. In the second Al site, Al(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. 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 Al(2)O6 octahedra and corners with five equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-56°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Al(1), one Al(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the fifth O site, O(5) is bonded in a water-like geometry to one Al(1) and one Al(2) atom.
Al3(SiO5)2 crystallizes in the triclinic P-1 space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(2) atoms to form AlO6 octahedra that share corners with five equivalent Si(1)O4 tetrahedra,  an edgeedge with one Al(2)O6 octahedra, and edges with two equivalent Al(1)O6 octahedra. The Al(1)-O(3) bond length is 1.97 Å. The Al(1)-O(5) bond length is 1.90 Å. There is one shorter (1.88 Å) and one longer (1.95 Å) Al(1)-O(1) bond length. There is one shorter (1.90 Å) and one longer (1.92 Å) Al(1)-O(2) bond length. In the second Al site, Al(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. Both Al(2)-O(3) bond lengths are 1.96 Å. Both Al(2)-O(4) bond lengths are 1.86 Å. Both Al(2)-O(5) bond lengths are 1.89 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 Al(2)O6 octahedra and corners with five equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-56°. The Si(1)-O(1) bond length is 1.67 Å. The Si(1)-O(2) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.63 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Al(1), one Al(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the fifth O site, O(5) is bonded in a water-like geometry to one Al(1) and one Al(2) atom.