CaAl2(SiO5)2 crystallizes in the monoclinic P2_1/m space group. Ca(1) is bonded in a 4-coordinate geometry to one O(1), one O(6), and two equivalent O(3) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) 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)O5 trigonal bipyramids and edges with two equivalent Al(2)O6 octahedra. In the second Al site, Al(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form distorted AlO6 octahedra that share edges with two equivalent Al(1)O6 octahedra and edges with two equivalent Si(1)O5 trigonal bipyramids. Si(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form SiO5 trigonal bipyramids that share corners with two equivalent Al(1)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, and  an edgeedge with one Si(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 35-42°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a distorted water-like 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 one Ca(1), one Al(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one O(4) atom. In the fifth O site, O(5) is bonded in a T-shaped geometry to one Al(1), one Al(2), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1) and two equivalent Si(1) atoms.
CaAl2(SiO5)2 crystallizes in the monoclinic P2_1/m space group. Ca(1) is bonded in a 4-coordinate geometry to one O(1), one O(6), and two equivalent O(3) atoms. The Ca(1)-O(1) bond length is 2.24 Å. The Ca(1)-O(6) bond length is 2.38 Å. Both Ca(1)-O(3) bond lengths are 2.33 Å. There are two inequivalent Al sites. In the first Al site, Al(1) 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)O5 trigonal bipyramids and edges with two equivalent Al(2)O6 octahedra. Both Al(1)-O(3) bond lengths are 1.82 Å. Both Al(1)-O(4) bond lengths are 2.12 Å. Both Al(1)-O(5) bond lengths are 1.93 Å. In the second Al site, Al(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form distorted AlO6 octahedra that share edges with two equivalent Al(1)O6 octahedra and edges with two equivalent Si(1)O5 trigonal bipyramids. Both Al(2)-O(2) bond lengths are 1.86 Å. Both Al(2)-O(4) bond lengths are 1.97 Å. Both Al(2)-O(5) bond lengths are 1.97 Å. Si(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form SiO5 trigonal bipyramids that share corners with two equivalent Al(1)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, and  an edgeedge with one Si(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 35-42°. The Si(1)-O(1) bond length is 1.76 Å. The Si(1)-O(2) bond length is 1.70 Å. The Si(1)-O(3) bond length is 1.68 Å. The Si(1)-O(5) bond length is 1.84 Å. The Si(1)-O(6) bond length is 1.74 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a distorted water-like 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 one Ca(1), one Al(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one O(4) atom. The O(4)-O(4) bond length is 1.41 Å. In the fifth O site, O(5) is bonded in a T-shaped geometry to one Al(1), one Al(2), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1) and two equivalent Si(1) atoms.