Ca3Si2O7 is Esseneite-derived structured and crystallizes in the orthorhombic Ima2 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(8) atom to form distorted CaO6 octahedra that share corners with two equivalent Ca(3)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra,  an edgeedge with one Ca(3)O6 octahedra, and  an edgeedge with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-72°. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. In the third Ca site, Ca(3) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form CaO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  an edgeedge with one Ca(1)O6 octahedra,  an edgeedge with one Ca(3)O6 octahedra,  an edgeedge with one Ca(4)O6 octahedra,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 62-72°. In the fourth Ca site, Ca(4) is bonded to one O(3), one O(7), two equivalent O(6), and two equivalent O(8) atoms to form distorted CaO6 octahedra that share corners with four equivalent Ca(1)O6 octahedra, corners with four equivalent Ca(3)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Ca(3)O6 octahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-65°. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(7), and two equivalent O(6) atoms to form SiO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Ca(3)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra,  an edgeedge with one Ca(4)O6 octahedra, and edges with two equivalent Ca(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-59°. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(4), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(3)O6 octahedra,  a cornercorner with one Ca(4)O6 octahedra, corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra,  an edgeedge with one Ca(1)O6 octahedra, and  an edgeedge with one Ca(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-62°. In the third Si site, Si(3) is bonded to two equivalent O(4) and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 53-69°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Ca(4), two equivalent Ca(3), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Si(2), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one Si(3) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Ca(3), one Ca(4), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Ca(4), two equivalent Ca(3), and one Si(1) atom. In the eighth O site, O(8) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Ca(3), one Ca(4), and one Si(2) atom.
Ca3Si2O7 is Esseneite-derived structured and crystallizes in the orthorhombic Ima2 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(8) atom to form distorted CaO6 octahedra that share corners with two equivalent Ca(3)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra,  an edgeedge with one Ca(3)O6 octahedra, and  an edgeedge with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-72°. The Ca(1)-O(1) bond length is 2.35 Å. The Ca(1)-O(2) bond length is 2.49 Å. The Ca(1)-O(4) bond length is 2.52 Å. The Ca(1)-O(5) bond length is 2.24 Å. The Ca(1)-O(6) bond length is 2.27 Å. The Ca(1)-O(8) bond length is 2.48 Å. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. Both Ca(2)-O(1) bond lengths are 2.63 Å. Both Ca(2)-O(2) bond lengths are 2.68 Å. Both Ca(2)-O(4) bond lengths are 2.60 Å. Both Ca(2)-O(5) bond lengths are 2.37 Å. In the third Ca site, Ca(3) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form CaO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  an edgeedge with one Ca(1)O6 octahedra,  an edgeedge with one Ca(3)O6 octahedra,  an edgeedge with one Ca(4)O6 octahedra,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 62-72°. The Ca(3)-O(1) bond length is 2.34 Å. The Ca(3)-O(2) bond length is 2.36 Å. The Ca(3)-O(3) bond length is 2.40 Å. The Ca(3)-O(6) bond length is 2.38 Å. The Ca(3)-O(7) bond length is 2.46 Å. The Ca(3)-O(8) bond length is 2.47 Å. In the fourth Ca site, Ca(4) is bonded to one O(3), one O(7), two equivalent O(6), and two equivalent O(8) atoms to form distorted CaO6 octahedra that share corners with four equivalent Ca(1)O6 octahedra, corners with four equivalent Ca(3)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Ca(3)O6 octahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-65°. The Ca(4)-O(3) bond length is 2.33 Å. The Ca(4)-O(7) bond length is 2.53 Å. Both Ca(4)-O(6) bond lengths are 2.46 Å. Both Ca(4)-O(8) bond lengths are 2.37 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(7), and two equivalent O(6) atoms to form SiO4 tetrahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Ca(3)O6 octahedra, corners with two equivalent Ca(4)O6 octahedra,  an edgeedge with one Ca(4)O6 octahedra, and edges with two equivalent Ca(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-59°. The Si(1)-O(3) bond length is 1.67 Å. The Si(1)-O(7) bond length is 1.64 Å. Both Si(1)-O(6) bond lengths are 1.66 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(4), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(3)O6 octahedra,  a cornercorner with one Ca(4)O6 octahedra, corners with two equivalent Ca(1)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra,  an edgeedge with one Ca(1)O6 octahedra, and  an edgeedge with one Ca(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-62°. The Si(2)-O(1) bond length is 1.64 Å. The Si(2)-O(2) bond length is 1.63 Å. The Si(2)-O(4) bond length is 1.73 Å. The Si(2)-O(8) bond length is 1.65 Å. In the third Si site, Si(3) is bonded to two equivalent O(4) and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 53-69°. Both Si(3)-O(4) bond lengths are 1.69 Å. Both Si(3)-O(5) bond lengths are 1.61 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Ca(4), two equivalent Ca(3), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Si(2), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one Si(3) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Ca(3), one Ca(4), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Ca(4), two equivalent Ca(3), and one Si(1) atom. In the eighth O site, O(8) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Ca(3), one Ca(4), and one Si(2) atom.