CaAl2SiO6 is Esseneite-like structured and crystallizes in the monoclinic C2 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(3)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-62°. In the second Al site, Al(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form AlO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Al(1)O4 tetrahedra, and edges with two equivalent Al(3)O6 octahedra. In the third Al site, Al(3) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with two equivalent Al(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Al(2)O6 octahedra. Si(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O6 octahedra, corners with two equivalent Al(3)O6 octahedra, and corners with two equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-60°. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Al(1), one Al(2), and one Al(3) atom to form a mixture of distorted corner and edge-sharing OCaAl3 tetrahedra. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Ca(2), one Al(1), and one Al(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(2), one Al(2), one Al(3), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Ca(1), one Al(3), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(1), and one Si(1) atom.
CaAl2SiO6 is Esseneite-like structured and crystallizes in the monoclinic C2 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms. Both Ca(1)-O(1) bond lengths are 2.40 Å. Both Ca(1)-O(3) bond lengths are 2.47 Å. Both Ca(1)-O(5) bond lengths are 2.48 Å. Both Ca(1)-O(6) bond lengths are 2.58 Å. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. Both Ca(2)-O(2) bond lengths are 2.39 Å. Both Ca(2)-O(3) bond lengths are 2.57 Å. Both Ca(2)-O(4) bond lengths are 2.44 Å. Both Ca(2)-O(6) bond lengths are 2.52 Å. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(3)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-62°. The Al(1)-O(1) bond length is 1.78 Å. The Al(1)-O(2) bond length is 1.74 Å. The Al(1)-O(3) bond length is 1.77 Å. The Al(1)-O(6) bond length is 1.79 Å. In the second Al site, Al(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form AlO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Al(1)O4 tetrahedra, and edges with two equivalent Al(3)O6 octahedra. Both Al(2)-O(1) bond lengths are 2.02 Å. Both Al(2)-O(2) bond lengths are 1.85 Å. Both Al(2)-O(4) bond lengths are 2.03 Å. In the third Al site, Al(3) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with two equivalent Al(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Al(2)O6 octahedra. Both Al(3)-O(1) bond lengths are 1.90 Å. Both Al(3)-O(4) bond lengths are 2.07 Å. Both Al(3)-O(5) bond lengths are 1.93 Å. Si(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O6 octahedra, corners with two equivalent Al(3)O6 octahedra, and corners with two equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-60°. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.66 Å. The Si(1)-O(5) bond length is 1.63 Å. The Si(1)-O(6) bond length is 1.64 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Al(1), one Al(2), and one Al(3) atom to form a mixture of distorted corner and edge-sharing OCaAl3 tetrahedra. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Ca(2), one Al(1), and one Al(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(2), one Al(2), one Al(3), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Ca(1), one Al(3), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(1), and one Si(1) atom.