CaMg3(SiO3)4 is Esseneite-like structured and crystallizes in the monoclinic C2 space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Mg(2)O6 octahedra. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. In the third Mg site, Mg(3) is bonded in a rectangular see-saw-like geometry to two equivalent O(2) and two equivalent O(3) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(1)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-59°. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-60°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Mg(1), one Mg(2), and one Si(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), one Mg(3), and one Si(2) atom to form a mixture of distorted corner and edge-sharing OMg3Si trigonal pyramids. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(3), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ca(1), one Mg(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom.
CaMg3(SiO3)4 is Esseneite-like structured and crystallizes in the monoclinic C2 space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. Both Ca(1)-O(1) bond lengths are 2.37 Å. Both Ca(1)-O(4) bond lengths are 2.29 Å. Both Ca(1)-O(5) bond lengths are 2.52 Å. Both Ca(1)-O(6) bond lengths are 2.79 Å. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Mg(2)O6 octahedra. Both Mg(1)-O(1) bond lengths are 2.19 Å. Both Mg(1)-O(2) bond lengths are 2.06 Å. Both Mg(1)-O(3) bond lengths are 2.10 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. Both Mg(2)-O(1) bond lengths are 2.09 Å. Both Mg(2)-O(2) bond lengths are 2.21 Å. Both Mg(2)-O(4) bond lengths are 2.05 Å. In the third Mg site, Mg(3) is bonded in a rectangular see-saw-like geometry to two equivalent O(2) and two equivalent O(3) atoms. Both Mg(3)-O(2) bond lengths are 2.04 Å. Both Mg(3)-O(3) bond lengths are 2.06 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(1)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-59°. The Si(1)-O(1) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.69 Å. The Si(1)-O(6) bond length is 1.68 Å. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-60°. The Si(2)-O(2) bond length is 1.63 Å. The Si(2)-O(4) bond length is 1.60 Å. The Si(2)-O(5) bond length is 1.69 Å. The Si(2)-O(6) bond length is 1.66 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), one Mg(1), one Mg(2), and one Si(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), one Mg(3), and one Si(2) atom to form a mixture of distorted corner and edge-sharing OMg3Si trigonal pyramids. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(3), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ca(1), one Mg(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom.