Ca2CoSi2O7 crystallizes in the tetragonal P-42_1m space group. Ca(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent O(2), and four equivalent O(3) atoms. Co(1) is bonded to four equivalent O(3) atoms to form CoO4 tetrahedra that share corners with four equivalent Si(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Co(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to two equivalent Ca(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to three equivalent Ca(1) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Co(1), and one Si(1) atom.
Ca2CoSi2O7 crystallizes in the tetragonal P-42_1m space group. Ca(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent O(2), and four equivalent O(3) atoms. The Ca(1)-O(1) bond length is 2.49 Å. There is one shorter (2.44 Å) and two longer (2.79 Å) Ca(1)-O(2) bond lengths. There are two shorter (2.41 Å) and two longer (2.69 Å) Ca(1)-O(3) bond lengths. Co(1) is bonded to four equivalent O(3) atoms to form CoO4 tetrahedra that share corners with four equivalent Si(1)O4 tetrahedra. All Co(1)-O(3) bond lengths are 1.96 Å. Si(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Co(1)O4 tetrahedra. The Si(1)-O(1) bond length is 1.68 Å. The Si(1)-O(2) bond length is 1.61 Å. Both Si(1)-O(3) bond lengths are 1.64 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to two equivalent Ca(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to three equivalent Ca(1) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Co(1), and one Si(1) atom.