BaCa2MgSi2O8 crystallizes in the trigonal P-3 space group. Ba(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form BaO12 cuboctahedra that share edges with six equivalent Ba(1)O12 cuboctahedra, edges with six equivalent Si(1)O4 tetrahedra, and faces with two equivalent Mg(1)O6 octahedra. Ca(1) is bonded in a 4-coordinate geometry to one O(1) and three equivalent O(2) atoms. Mg(1) is bonded to six equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Si(1)O4 tetrahedra and faces with two equivalent Ba(1)O12 cuboctahedra. Si(1) is bonded to one O(1) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 24°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to three equivalent Ba(1), one Ca(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ba(1), one Ca(1), one Mg(1), and one Si(1) atom.
BaCa2MgSi2O8 crystallizes in the trigonal P-3 space group. Ba(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form BaO12 cuboctahedra that share edges with six equivalent Ba(1)O12 cuboctahedra, edges with six equivalent Si(1)O4 tetrahedra, and faces with two equivalent Mg(1)O6 octahedra. All Ba(1)-O(1) bond lengths are 3.17 Å. All Ba(1)-O(2) bond lengths are 2.82 Å. Ca(1) is bonded in a 4-coordinate geometry to one O(1) and three equivalent O(2) atoms. The Ca(1)-O(1) bond length is 2.28 Å. All Ca(1)-O(2) bond lengths are 2.42 Å. Mg(1) is bonded to six equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Si(1)O4 tetrahedra and faces with two equivalent Ba(1)O12 cuboctahedra. All Mg(1)-O(2) bond lengths are 2.10 Å. Si(1) is bonded to one O(1) and three equivalent O(2) atoms to form SiO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 24°. The Si(1)-O(1) bond length is 1.62 Å. All Si(1)-O(2) bond lengths are 1.66 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to three equivalent Ba(1), one Ca(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ba(1), one Ca(1), one Mg(1), and one Si(1) atom.