Ca2Al2SiO7 crystallizes in the orthorhombic P2_12_12_1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(1), one O(4), one O(7), and two equivalent O(5) atoms. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(5), and two equivalent O(3) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form distorted AlO4 trigonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Al(2)O5 trigonal bipyramid, and  an edgeedge with one Al(2)O5 trigonal bipyramid. In the second Al site, Al(2) is bonded to one O(1), one O(4), one O(5), one O(6), and one O(7) atom to form AlO5 trigonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Al(1)O4 trigonal pyramid, and  an edgeedge with one Al(1)O4 trigonal pyramid. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Al(2)O5 trigonal bipyramids and corners with two equivalent Al(1)O4 trigonal pyramids. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(2), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ca(2), one Al(1), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ca(2) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(1), and one Al(2) atom. In the fifth O site, O(5) is bonded to one Ca(2), two equivalent Ca(1), and one Al(2) atom to form distorted corner-sharing OCa3Al tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Al(1), one Al(2), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Al(2) atom.
Ca2Al2SiO7 crystallizes in the orthorhombic P2_12_12_1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(1), one O(4), one O(7), and two equivalent O(5) atoms. The Ca(1)-O(1) bond length is 2.64 Å. The Ca(1)-O(4) bond length is 2.30 Å. The Ca(1)-O(7) bond length is 2.27 Å. There is one shorter (2.27 Å) and one longer (2.35 Å) Ca(1)-O(5) bond length. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(5), and two equivalent O(3) atoms. The Ca(2)-O(1) bond length is 2.49 Å. The Ca(2)-O(2) bond length is 2.67 Å. The Ca(2)-O(4) bond length is 2.72 Å. The Ca(2)-O(5) bond length is 2.24 Å. There is one shorter (2.29 Å) and one longer (2.40 Å) Ca(2)-O(3) bond length. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form distorted AlO4 trigonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Al(2)O5 trigonal bipyramid, and  an edgeedge with one Al(2)O5 trigonal bipyramid. The Al(1)-O(2) bond length is 1.78 Å. The Al(1)-O(4) bond length is 1.75 Å. The Al(1)-O(6) bond length is 1.90 Å. The Al(1)-O(7) bond length is 1.75 Å. In the second Al site, Al(2) is bonded to one O(1), one O(4), one O(5), one O(6), and one O(7) atom to form AlO5 trigonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Al(1)O4 trigonal pyramid, and  an edgeedge with one Al(1)O4 trigonal pyramid. The Al(2)-O(1) bond length is 1.86 Å. The Al(2)-O(4) bond length is 2.01 Å. The Al(2)-O(5) bond length is 1.76 Å. The Al(2)-O(6) bond length is 1.95 Å. The Al(2)-O(7) bond length is 1.89 Å. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Al(2)O5 trigonal bipyramids and corners with two equivalent Al(1)O4 trigonal pyramids. The Si(1)-O(1) bond length is 1.65 Å. The Si(1)-O(2) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.63 Å. The Si(1)-O(6) bond length is 1.69 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(2), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ca(2), one Al(1), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ca(2) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(1), and one Al(2) atom. In the fifth O site, O(5) is bonded to one Ca(2), two equivalent Ca(1), and one Al(2) atom to form distorted corner-sharing OCa3Al tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Al(1), one Al(2), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Al(2) atom.