Ca2Ga2SiO7 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(7), two equivalent O(3), and two equivalent O(6) atoms. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(6), two equivalent O(2), and two equivalent O(7) atoms. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form GaO4 tetrahedra that share corners with two equivalent Ga(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the second Ga site, Ga(2) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form GaO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Ga(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(2), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ga(2)O4 tetrahedra and corners with two equivalent Ga(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(2), one Ga(2), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCa2GaSi tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ca(2), one Ga(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 Ga(1), and one Ga(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ga(1), and one Ga(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Ca(1), one Ca(2), one Ga(1), and one Si(1) atom. In the sixth O site, O(6) is bonded to one Ca(2), two equivalent Ca(1), and one Ga(2) atom to form OCa3Ga tetrahedra that share corners with two equivalent O(1)Ca2GaSi tetrahedra, corners with two equivalent O(6)Ca3Ga tetrahedra, and  an edgeedge with one O(1)Ca2GaSi tetrahedra. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom.
Ca2Ga2SiO7 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(7), two equivalent O(3), and two equivalent O(6) atoms. The Ca(1)-O(1) bond length is 2.48 Å. The Ca(1)-O(4) bond length is 2.38 Å. The Ca(1)-O(5) bond length is 3.03 Å. The Ca(1)-O(7) bond length is 2.78 Å. There is one shorter (2.45 Å) and one longer (2.80 Å) Ca(1)-O(3) bond length. There is one shorter (2.45 Å) and one longer (2.52 Å) Ca(1)-O(6) bond length. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(6), two equivalent O(2), and two equivalent O(7) atoms. The Ca(2)-O(1) bond length is 2.43 Å. The Ca(2)-O(4) bond length is 2.74 Å. The Ca(2)-O(5) bond length is 2.50 Å. The Ca(2)-O(6) bond length is 2.41 Å. There is one shorter (2.43 Å) and one longer (2.97 Å) Ca(2)-O(2) bond length. There is one shorter (2.61 Å) and one longer (2.68 Å) Ca(2)-O(7) bond length. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form GaO4 tetrahedra that share corners with two equivalent Ga(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. The Ga(1)-O(2) bond length is 1.87 Å. The Ga(1)-O(3) bond length is 1.84 Å. The Ga(1)-O(4) bond length is 1.84 Å. The Ga(1)-O(5) bond length is 1.86 Å. In the second Ga site, Ga(2) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form GaO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Ga(1)O4 tetrahedra. The Ga(2)-O(1) bond length is 1.89 Å. The Ga(2)-O(3) bond length is 1.87 Å. The Ga(2)-O(4) bond length is 1.87 Å. The Ga(2)-O(6) bond length is 1.80 Å. Si(1) is bonded to one O(1), one O(2), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ga(2)O4 tetrahedra and corners with two equivalent Ga(1)O4 tetrahedra. The Si(1)-O(1) bond length is 1.66 Å. The Si(1)-O(2) bond length is 1.67 Å. The Si(1)-O(5) bond length is 1.66 Å. The Si(1)-O(7) bond length is 1.61 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(2), one Ga(2), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCa2GaSi tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ca(2), one Ga(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 Ga(1), and one Ga(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ga(1), and one Ga(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Ca(1), one Ca(2), one Ga(1), and one Si(1) atom. In the sixth O site, O(6) is bonded to one Ca(2), two equivalent Ca(1), and one Ga(2) atom to form OCa3Ga tetrahedra that share corners with two equivalent O(1)Ca2GaSi tetrahedra, corners with two equivalent O(6)Ca3Ga tetrahedra, and  an edgeedge with one O(1)Ca2GaSi tetrahedra. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom.