CaAl2Si4O15 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 6-coordinate geometry to one O(11), one O(12), one O(14), one O(15), one O(6), and one O(7) atom. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(11), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(12), one O(5), one O(7), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(11), one O(2), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(12), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(2), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(10), one O(3), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(4) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(3) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(4) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Si(3) and one Si(4) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(2) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one O(14) and one O(15) atom. In the fourteenth O site, O(14) is bonded in a water-like geometry to one Ca(1) and one O(13) atom. In the fifteenth O site, O(15) is bonded in an L-shaped geometry to one Ca(1) and one O(13) atom.
CaAl2Si4O15 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 6-coordinate geometry to one O(11), one O(12), one O(14), one O(15), one O(6), and one O(7) atom. The Ca(1)-O(11) bond length is 2.30 Å. The Ca(1)-O(12) bond length is 2.31 Å. The Ca(1)-O(14) bond length is 2.63 Å. The Ca(1)-O(15) bond length is 2.86 Å. The Ca(1)-O(6) bond length is 2.32 Å. The Ca(1)-O(7) bond length is 2.32 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(11), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. The Al(1)-O(11) bond length is 1.80 Å. The Al(1)-O(4) bond length is 1.73 Å. The Al(1)-O(6) bond length is 1.80 Å. The Al(1)-O(8) bond length is 1.73 Å. In the second Al site, Al(2) is bonded to one O(12), one O(5), one O(7), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. The Al(2)-O(12) bond length is 1.80 Å. The Al(2)-O(5) bond length is 1.73 Å. The Al(2)-O(7) bond length is 1.80 Å. The Al(2)-O(9) bond length is 1.73 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(11), one O(2), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(11) bond length is 1.66 Å. The Si(1)-O(2) bond length is 1.64 Å. The Si(1)-O(5) bond length is 1.60 Å. In the second Si site, Si(2) is bonded to one O(1), one O(12), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The Si(2)-O(1) bond length is 1.64 Å. The Si(2)-O(12) bond length is 1.66 Å. The Si(2)-O(3) bond length is 1.64 Å. The Si(2)-O(4) bond length is 1.60 Å. In the third Si site, Si(3) is bonded to one O(10), one O(2), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. The Si(3)-O(10) bond length is 1.65 Å. The Si(3)-O(2) bond length is 1.64 Å. The Si(3)-O(6) bond length is 1.65 Å. The Si(3)-O(8) bond length is 1.61 Å. In the fourth Si site, Si(4) is bonded to one O(10), one O(3), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. The Si(4)-O(10) bond length is 1.64 Å. The Si(4)-O(3) bond length is 1.63 Å. The Si(4)-O(7) bond length is 1.65 Å. The Si(4)-O(9) bond length is 1.61 Å. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(4) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(3) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(4) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Si(3) and one Si(4) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(2) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one O(14) and one O(15) atom. The O(13)-O(14) bond length is 1.31 Å. The O(13)-O(15) bond length is 1.29 Å. In the fourteenth O site, O(14) is bonded in a water-like geometry to one Ca(1) and one O(13) atom. In the fifteenth O site, O(15) is bonded in an L-shaped geometry to one Ca(1) and one O(13) atom.