Ca2Al2SiO7 crystallizes in the tetragonal P-42_1m space group. Ca(1) is bonded in a 8-coordinate geometry to one O(3), three equivalent O(1), and four equivalent O(2) atoms. Al(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form AlO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. Si(1) is bonded to four equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Al(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(1) and one Al(1) atom to form distorted OCa3Al tetrahedra that share corners with two equivalent O(3)Ca2Al2 tetrahedra, corners with four equivalent O(1)Ca3Al tetrahedra,  an edgeedge with one O(3)Ca2Al2 tetrahedra, and  an edgeedge with one O(1)Ca3Al tetrahedra. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ca(1), one Al(1), and one Si(1) atom. In the third O site, O(3) is bonded to two equivalent Ca(1) and two equivalent Al(1) atoms to form a mixture of distorted corner and edge-sharing OCa2Al2 tetrahedra.
Ca2Al2SiO7 crystallizes in the tetragonal P-42_1m space group. Ca(1) is bonded in a 8-coordinate geometry to one O(3), three equivalent O(1), and four equivalent O(2) atoms. The Ca(1)-O(3) bond length is 2.43 Å. There is one shorter (2.42 Å) and two longer (2.48 Å) Ca(1)-O(1) bond lengths. There are two shorter (2.50 Å) and two longer (2.99 Å) Ca(1)-O(2) bond lengths. Al(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form AlO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. The Al(1)-O(1) bond length is 1.73 Å. The Al(1)-O(3) bond length is 1.76 Å. Both Al(1)-O(2) bond lengths are 1.80 Å. Si(1) is bonded to four equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Al(1)O4 tetrahedra. All Si(1)-O(2) bond lengths are 1.65 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(1) and one Al(1) atom to form distorted OCa3Al tetrahedra that share corners with two equivalent O(3)Ca2Al2 tetrahedra, corners with four equivalent O(1)Ca3Al tetrahedra,  an edgeedge with one O(3)Ca2Al2 tetrahedra, and  an edgeedge with one O(1)Ca3Al tetrahedra. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ca(1), one Al(1), and one Si(1) atom. In the third O site, O(3) is bonded to two equivalent Ca(1) and two equivalent Al(1) atoms to form a mixture of distorted corner and edge-sharing OCa2Al2 tetrahedra.