Ca6Si6O19 crystallizes in the triclinic P-1 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(10), two equivalent O(3), and two equivalent O(4) atoms to form distorted CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Ca(2)O6 octahedra. In the second Ca site, Ca(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(9) atoms to form CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and edges with two equivalent Ca(1)O6 octahedra. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(10), one O(4), one O(5), one O(7), one O(9), and two equivalent O(8) atoms. In the fourth Ca site, Ca(4) is bonded in a 7-coordinate geometry to one O(10), one O(3), one O(6), one O(8), one O(9), and two equivalent O(7) atoms. There are three 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(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra,  a cornercorner with one Ca(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-60°. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra,  a cornercorner with one Ca(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-60°. In the third Si site, Si(3) is bonded to one O(1), one O(5), one O(6), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Si(3) atoms. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(4), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ca(3), one Si(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Ca(4), one Si(2), and one Si(3) atom. In the seventh O site, O(7) is bonded to one Ca(3), two equivalent Ca(4), and one Si(2) atom to form a mixture of distorted edge and corner-sharing OCa3Si trigonal pyramids. In the eighth O site, O(8) is bonded to one Ca(4), two equivalent Ca(3), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OCa3Si trigonal pyramids. In the ninth O site, O(9) is bonded to one Ca(2), one Ca(3), one Ca(4), and one Si(3) atom to form a mixture of distorted edge and corner-sharing OCa3Si tetrahedra. In the tenth O site, O(10) is bonded in a trigonal non-coplanar geometry to one Ca(1), one Ca(3), and one Ca(4) atom.
Ca6Si6O19 crystallizes in the triclinic P-1 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(10), two equivalent O(3), and two equivalent O(4) atoms to form distorted CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Ca(2)O6 octahedra. Both Ca(1)-O(10) bond lengths are 2.31 Å. Both Ca(1)-O(3) bond lengths are 2.40 Å. Both Ca(1)-O(4) bond lengths are 2.42 Å. In the second Ca site, Ca(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(9) atoms to form CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and edges with two equivalent Ca(1)O6 octahedra. Both Ca(2)-O(3) bond lengths are 2.43 Å. Both Ca(2)-O(4) bond lengths are 2.44 Å. Both Ca(2)-O(9) bond lengths are 2.38 Å. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(10), one O(4), one O(5), one O(7), one O(9), and two equivalent O(8) atoms. The Ca(3)-O(10) bond length is 2.33 Å. The Ca(3)-O(4) bond length is 2.68 Å. The Ca(3)-O(5) bond length is 2.83 Å. The Ca(3)-O(7) bond length is 2.40 Å. The Ca(3)-O(9) bond length is 2.39 Å. There is one shorter (2.36 Å) and one longer (2.45 Å) Ca(3)-O(8) bond length. In the fourth Ca site, Ca(4) is bonded in a 7-coordinate geometry to one O(10), one O(3), one O(6), one O(8), one O(9), and two equivalent O(7) atoms. The Ca(4)-O(10) bond length is 2.32 Å. The Ca(4)-O(3) bond length is 2.78 Å. The Ca(4)-O(6) bond length is 2.77 Å. The Ca(4)-O(8) bond length is 2.43 Å. The Ca(4)-O(9) bond length is 2.37 Å. There is one shorter (2.43 Å) and one longer (2.45 Å) Ca(4)-O(7) bond length. There are three 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(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra,  a cornercorner with one Ca(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-60°. The Si(1)-O(2) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.66 Å. The Si(1)-O(8) bond length is 1.63 Å. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra,  a cornercorner with one Ca(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-60°. The Si(2)-O(2) bond length is 1.65 Å. The Si(2)-O(3) bond length is 1.62 Å. The Si(2)-O(6) bond length is 1.67 Å. The Si(2)-O(7) bond length is 1.64 Å. In the third Si site, Si(3) is bonded to one O(1), one O(5), one O(6), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. The Si(3)-O(1) bond length is 1.62 Å. The Si(3)-O(5) bond length is 1.64 Å. The Si(3)-O(6) bond length is 1.64 Å. The Si(3)-O(9) bond length is 1.61 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Si(3) atoms. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(4), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ca(3), one Si(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Ca(4), one Si(2), and one Si(3) atom. In the seventh O site, O(7) is bonded to one Ca(3), two equivalent Ca(4), and one Si(2) atom to form a mixture of distorted edge and corner-sharing OCa3Si trigonal pyramids. In the eighth O site, O(8) is bonded to one Ca(4), two equivalent Ca(3), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OCa3Si trigonal pyramids. In the ninth O site, O(9) is bonded to one Ca(2), one Ca(3), one Ca(4), and one Si(3) atom to form a mixture of distorted edge and corner-sharing OCa3Si tetrahedra. In the tenth O site, O(10) is bonded in a trigonal non-coplanar geometry to one Ca(1), one Ca(3), and one Ca(4) atom.