Mg3Ca is beta-derived structured and crystallizes in the hexagonal P-6m2 space group. Ca(1) is bonded to six equivalent Ca(1) and six equivalent Mg(2) atoms to form CaCa6Mg6 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with twelve equivalent Mg(1)Mg12 cuboctahedra, edges with six equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with six equivalent Ca(1)Ca6Mg6 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(1)Mg12 cuboctahedra, corners with twelve equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with six equivalent Mg(1)Mg12 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with six equivalent Mg(1)Mg12 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded to three equivalent Ca(1), three equivalent Mg(1), and six equivalent Mg(2) atoms to form MgCa3Mg9 cuboctahedra that share corners with eighteen equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with six equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Mg(1)Mg12 cuboctahedra, faces with six equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with six equivalent Mg(1)Mg12 cuboctahedra, and faces with eight equivalent Mg(2)Ca3Mg9 cuboctahedra.
Mg3Ca is beta-derived structured and crystallizes in the hexagonal P-6m2 space group. Ca(1) is bonded to six equivalent Ca(1) and six equivalent Mg(2) atoms to form CaCa6Mg6 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with twelve equivalent Mg(1)Mg12 cuboctahedra, edges with six equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with six equivalent Ca(1)Ca6Mg6 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. All Ca(1)-Ca(1) bond lengths are 3.41 Å. All Ca(1)-Mg(2) bond lengths are 3.49 Å. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(1)Mg12 cuboctahedra, corners with twelve equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with six equivalent Mg(1)Mg12 cuboctahedra, edges with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra, faces with two equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with six equivalent Mg(1)Mg12 cuboctahedra, and faces with twelve equivalent Mg(2)Ca3Mg9 cuboctahedra. All Mg(1)-Mg(1) bond lengths are 3.41 Å. All Mg(1)-Mg(2) bond lengths are 3.23 Å. In the second Mg site, Mg(2) is bonded to three equivalent Ca(1), three equivalent Mg(1), and six equivalent Mg(2) atoms to form MgCa3Mg9 cuboctahedra that share corners with eighteen equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with six equivalent Mg(2)Ca3Mg9 cuboctahedra, edges with six equivalent Mg(1)Mg12 cuboctahedra, faces with six equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with six equivalent Mg(1)Mg12 cuboctahedra, and faces with eight equivalent Mg(2)Ca3Mg9 cuboctahedra. All Mg(2)-Mg(2) bond lengths are 3.41 Å.