Ca2Cr3O8 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(2)O6 octahedra,  an edgeedge with one Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 20-58°. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form CrO6 octahedra that share corners with six equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Cr(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with four equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Cr(2) atoms. In the second O site, O(2) is bonded in a distorted see-saw-like geometry to one Ca(1), one Cr(1), and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to two equivalent Ca(1), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OCa2Cr2 trigonal pyramids.
Ca2Cr3O8 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(2)O6 octahedra,  an edgeedge with one Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 20-58°. The Ca(1)-O(1) bond length is 2.30 Å. The Ca(1)-O(2) bond length is 2.34 Å. There are two shorter (2.33 Å) and two longer (2.45 Å) Ca(1)-O(3) bond lengths. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form CrO6 octahedra that share corners with six equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Cr(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. Both Cr(1)-O(2) bond lengths are 1.98 Å. All Cr(1)-O(3) bond lengths are 1.92 Å. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with four equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. Both Cr(2)-O(1) bond lengths are 1.90 Å. Both Cr(2)-O(2) bond lengths are 2.06 Å. Both Cr(2)-O(3) bond lengths are 1.92 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Cr(2) atoms. In the second O site, O(2) is bonded in a distorted see-saw-like geometry to one Ca(1), one Cr(1), and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to two equivalent Ca(1), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OCa2Cr2 trigonal pyramids.