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 7-coordinate geometry to one O(3), one O(4), one O(7), two equivalent O(1), and two equivalent O(5) atoms. In the second Ca site, Ca(2) is bonded in a 2-coordinate geometry to one O(1), 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 AlO4 tetrahedra that share  a cornercorner with one Al(2)O5 square pyramid, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Al(2)O5 square pyramid. 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 distorted AlO5 square pyramids that share  a cornercorner with one Al(1)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Al(1)O4 tetrahedra. 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 square pyramids and corners with two equivalent Al(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ca(2), two equivalent Ca(1), 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 Al(1) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Al(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one Al(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate 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 7-coordinate geometry to one O(3), one O(4), one O(7), two equivalent O(1), and two equivalent O(5) atoms. The Ca(1)-O(3) bond length is 2.40 Å. The Ca(1)-O(4) bond length is 2.37 Å. The Ca(1)-O(7) bond length is 2.47 Å. There is one shorter (2.28 Å) and one longer (2.61 Å) Ca(1)-O(1) bond length. There is one shorter (2.46 Å) and one longer (2.54 Å) Ca(1)-O(5) bond length. In the second Ca site, Ca(2) is bonded in a 2-coordinate geometry to one O(1), one O(5), and two equivalent O(3) atoms. The Ca(2)-O(1) bond length is 2.79 Å. The Ca(2)-O(5) bond length is 2.15 Å. There is one shorter (2.17 Å) and one longer (2.61 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 AlO4 tetrahedra that share  a cornercorner with one Al(2)O5 square pyramid, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Al(2)O5 square pyramid. The Al(1)-O(2) bond length is 1.78 Å. The Al(1)-O(4) bond length is 1.76 Å. The Al(1)-O(6) bond length is 1.97 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 distorted AlO5 square pyramids that share  a cornercorner with one Al(1)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Al(1)O4 tetrahedra. The Al(2)-O(1) bond length is 1.92 Å. The Al(2)-O(4) bond length is 1.88 Å. The Al(2)-O(5) bond length is 1.76 Å. The Al(2)-O(6) bond length is 1.92 Å. The Al(2)-O(7) bond length is 1.87 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 square pyramids and corners with two equivalent Al(1)O4 tetrahedra. The Si(1)-O(1) bond length is 1.63 Å. The Si(1)-O(2) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(6) bond length is 1.67 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ca(2), two equivalent Ca(1), 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 Al(1) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Al(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one Al(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Al(2) atom.