CaMn2(SiO3)4 crystallizes in the monoclinic C2 space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mn(2)O6 octahedra. In the second Mn site, Mn(2) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Mn(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-61°. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(2)O6 octahedra, corners with two equivalent Mn(1)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-59°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Mn(2) 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 Mn(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one Si(2) atom. In the sixth O site, O(6) is bonded to one Ca(1), one Mn(1), one Mn(2), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OCaMn2Si tetrahedra.
CaMn2(SiO3)4 crystallizes in the monoclinic C2 space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms. Both Ca(1)-O(1) bond lengths are 2.45 Å. Both Ca(1)-O(2) bond lengths are 2.77 Å. Both Ca(1)-O(4) bond lengths are 2.33 Å. Both Ca(1)-O(6) bond lengths are 2.45 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mn(2)O6 octahedra. Both Mn(1)-O(4) bond lengths are 2.06 Å. Both Mn(1)-O(5) bond lengths are 2.14 Å. Both Mn(1)-O(6) bond lengths are 1.95 Å. In the second Mn site, Mn(2) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Mn(1)O6 octahedra. Both Mn(2)-O(3) bond lengths are 1.98 Å. Both Mn(2)-O(5) bond lengths are 1.94 Å. Both Mn(2)-O(6) bond lengths are 2.30 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-61°. The Si(1)-O(1) bond length is 1.66 Å. The Si(1)-O(2) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.59 Å. The Si(1)-O(6) bond length is 1.68 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(2)O6 octahedra, corners with two equivalent Mn(1)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-59°. The Si(2)-O(1) bond length is 1.67 Å. The Si(2)-O(2) bond length is 1.65 Å. The Si(2)-O(4) bond length is 1.62 Å. The Si(2)-O(5) bond length is 1.65 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Mn(2) 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 Mn(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one Si(2) atom. In the sixth O site, O(6) is bonded to one Ca(1), one Mn(1), one Mn(2), and one Si(1) atom to form a mixture of distorted edge and corner-sharing OCaMn2Si tetrahedra.