CaSi2O5 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 9-coordinate geometry to one O(10), one O(2), one O(3), one O(5), one O(9), two equivalent O(4), and two equivalent O(7) atoms. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(2), one O(5), one O(6), one O(9), and two equivalent O(8) atoms. There are five inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(10), one O(2), one O(4), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(4)O6 octahedra,  a cornercorner with one Si(5)O6 octahedra, and  a cornercorner with one Si(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-55°. In the second Si site, Si(2) is bonded to one O(1), one O(5), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(4)O6 octahedra,  a cornercorner with one Si(5)O6 octahedra, and corners with two equivalent Si(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 36-57°. In the third Si site, Si(3) is bonded to one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form SiO5 trigonal bipyramids that share  a cornercorner with one Si(4)O6 octahedra,  a cornercorner with one Si(5)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 36°. In the fourth Si site, Si(4) is bonded to two equivalent O(4), two equivalent O(6), and two equivalent O(9) atoms to form SiO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O5 trigonal bipyramids. In the fifth Si site, Si(5) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form SiO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O5 trigonal bipyramids. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(2), one Si(2), and one Si(5) atom. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), one Si(1), and one Si(5) atom to form distorted corner-sharing OCa2Si2 tetrahedra. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Si(3), and one Si(5) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Ca(1), one Si(1), and one Si(4) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Ca(2), one Si(2), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(2), one Si(3), and one Si(4) atom. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Si(2), and one Si(3) atom to form a mixture of distorted corner and edge-sharing OCa2Si2 tetrahedra. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to two equivalent Ca(2), one Si(1), and one Si(3) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Si(2), and one Si(4) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one Si(1) atom.
CaSi2O5 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 9-coordinate geometry to one O(10), one O(2), one O(3), one O(5), one O(9), two equivalent O(4), and two equivalent O(7) atoms. The Ca(1)-O(10) bond length is 2.32 Å. The Ca(1)-O(2) bond length is 2.43 Å. The Ca(1)-O(3) bond length is 2.36 Å. The Ca(1)-O(5) bond length is 3.08 Å. The Ca(1)-O(9) bond length is 2.62 Å. There is one shorter (2.62 Å) and one longer (2.94 Å) Ca(1)-O(4) bond length. There is one shorter (2.46 Å) and one longer (2.52 Å) Ca(1)-O(7) bond length. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(2), one O(5), one O(6), one O(9), and two equivalent O(8) atoms. The Ca(2)-O(1) bond length is 2.48 Å. The Ca(2)-O(10) bond length is 2.41 Å. The Ca(2)-O(2) bond length is 2.40 Å. The Ca(2)-O(5) bond length is 2.51 Å. The Ca(2)-O(6) bond length is 2.32 Å. The Ca(2)-O(9) bond length is 2.48 Å. There is one shorter (2.50 Å) and one longer (2.52 Å) Ca(2)-O(8) bond length. There are five inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(10), one O(2), one O(4), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(4)O6 octahedra,  a cornercorner with one Si(5)O6 octahedra, and  a cornercorner with one Si(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-55°. The Si(1)-O(10) bond length is 1.61 Å. The Si(1)-O(2) bond length is 1.66 Å. The Si(1)-O(4) bond length is 1.65 Å. The Si(1)-O(8) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(1), one O(5), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(4)O6 octahedra,  a cornercorner with one Si(5)O6 octahedra, and corners with two equivalent Si(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 36-57°. The Si(2)-O(1) bond length is 1.63 Å. The Si(2)-O(5) bond length is 1.66 Å. The Si(2)-O(7) bond length is 1.65 Å. The Si(2)-O(9) bond length is 1.65 Å. In the third Si site, Si(3) is bonded to one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form SiO5 trigonal bipyramids that share  a cornercorner with one Si(4)O6 octahedra,  a cornercorner with one Si(5)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 36°. The Si(3)-O(3) bond length is 1.69 Å. The Si(3)-O(5) bond length is 1.71 Å. The Si(3)-O(6) bond length is 1.71 Å. The Si(3)-O(7) bond length is 1.84 Å. The Si(3)-O(8) bond length is 1.79 Å. In the fourth Si site, Si(4) is bonded to two equivalent O(4), two equivalent O(6), and two equivalent O(9) atoms to form SiO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O5 trigonal bipyramids. Both Si(4)-O(4) bond lengths are 1.81 Å. Both Si(4)-O(6) bond lengths are 1.78 Å. Both Si(4)-O(9) bond lengths are 1.88 Å. In the fifth Si site, Si(5) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form SiO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O5 trigonal bipyramids. Both Si(5)-O(1) bond lengths are 1.86 Å. Both Si(5)-O(2) bond lengths are 1.81 Å. Both Si(5)-O(3) bond lengths are 1.76 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(2), one Si(2), and one Si(5) atom. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), one Si(1), and one Si(5) atom to form distorted corner-sharing OCa2Si2 tetrahedra. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Si(3), and one Si(5) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Ca(1), one Si(1), and one Si(4) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Ca(2), one Si(2), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(2), one Si(3), and one Si(4) atom. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Si(2), and one Si(3) atom to form a mixture of distorted corner and edge-sharing OCa2Si2 tetrahedra. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to two equivalent Ca(2), one Si(1), and one Si(3) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Si(2), and one Si(4) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one Si(1) atom.