CaAl2(SiO5)2 crystallizes in the orthorhombic Cmcm space group. Ca(1) is bonded to one O(1), one O(5), and four equivalent O(2) atoms to form CaO6 octahedra that share corners with four equivalent Al(1)O6 octahedra and corners with six equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. Al(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form AlO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles are 58°. Si(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra, corners with four equivalent Al(1)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-66°. There are five inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Al(1) and one O(4) atom. In the second O site, O(5) is bonded in a single-bond geometry to one Ca(1) atom. In the third O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Si(1) atoms. In the fourth O site, O(2) is bonded in a trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. In the fifth O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one Si(1) atom.
CaAl2(SiO5)2 crystallizes in the orthorhombic Cmcm space group. Ca(1) is bonded to one O(1), one O(5), and four equivalent O(2) atoms to form CaO6 octahedra that share corners with four equivalent Al(1)O6 octahedra and corners with six equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. The Ca(1)-O(1) bond length is 2.40 Å. The Ca(1)-O(5) bond length is 2.36 Å. All Ca(1)-O(2) bond lengths are 2.45 Å. Al(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form AlO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles are 58°. Both Al(1)-O(2) bond lengths are 1.83 Å. Both Al(1)-O(3) bond lengths are 1.96 Å. Both Al(1)-O(4) bond lengths are 2.09 Å. Si(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra, corners with four equivalent Al(1)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-66°. The Si(1)-O(1) bond length is 1.67 Å. The Si(1)-O(3) bond length is 1.66 Å. Both Si(1)-O(2) bond lengths are 1.62 Å. There are five inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Al(1) and one O(4) atom. The O(4)-O(4) bond length is 1.47 Å. In the second O site, O(5) is bonded in a single-bond geometry to one Ca(1) atom. In the third O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Si(1) atoms. In the fourth O site, O(2) is bonded in a trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. In the fifth O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one Si(1) atom.