CaAl2Si2O8 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 7-coordinate geometry to one O(2), one O(5), one O(6), one O(7), one O(8), and two equivalent O(1) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(3), one O(6), one O(7), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(4), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ca(1), one Al(2), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Al(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Ca(1), one Al(1), and one Al(2) atom.
CaAl2Si2O8 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 7-coordinate geometry to one O(2), one O(5), one O(6), one O(7), one O(8), and two equivalent O(1) atoms. The Ca(1)-O(2) bond length is 2.46 Å. The Ca(1)-O(5) bond length is 2.94 Å. The Ca(1)-O(6) bond length is 2.77 Å. The Ca(1)-O(7) bond length is 2.31 Å. The Ca(1)-O(8) bond length is 2.33 Å. There is one shorter (2.38 Å) and one longer (3.00 Å) Ca(1)-O(1) bond length. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(3), one O(6), one O(7), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The Al(1)-O(3) bond length is 1.73 Å. The Al(1)-O(6) bond length is 1.78 Å. The Al(1)-O(7) bond length is 1.79 Å. The Al(1)-O(8) bond length is 1.75 Å. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(4), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. The Al(2)-O(1) bond length is 1.78 Å. The Al(2)-O(2) bond length is 1.79 Å. The Al(2)-O(4) bond length is 1.73 Å. The Al(2)-O(8) bond length is 1.74 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. The Si(1)-O(2) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.65 Å. The Si(1)-O(7) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. The Si(2)-O(1) bond length is 1.66 Å. The Si(2)-O(3) bond length is 1.61 Å. The Si(2)-O(5) bond length is 1.65 Å. The Si(2)-O(6) bond length is 1.64 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ca(1), one Al(2), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Al(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Ca(1), one Al(1), and one Al(2) atom.