Ca7Mg6Si14 crystallizes in the hexagonal P6/mmm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 13-coordinate geometry to four equivalent Mg(1), one Si(3), four equivalent Si(1), and four equivalent Si(2) atoms. In the second Ca site, Ca(2) is bonded to twelve equivalent Si(2) atoms to form face-sharing CaSi12 cuboctahedra. Mg(1) is bonded to four equivalent Ca(1), two equivalent Si(1), and two equivalent Si(3) atoms to form a mixture of distorted face and edge-sharing MgCa4Si4 tetrahedra. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to four equivalent Ca(1), two equivalent Mg(1), and one Si(2) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Ca(2), four equivalent Ca(1), one Si(1), and two equivalent Si(2) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to three equivalent Ca(1) and six equivalent Mg(1) atoms.
Ca7Mg6Si14 crystallizes in the hexagonal P6/mmm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 13-coordinate geometry to four equivalent Mg(1), one Si(3), four equivalent Si(1), and four equivalent Si(2) atoms. All Ca(1)-Mg(1) bond lengths are 3.55 Å. The Ca(1)-Si(3) bond length is 3.29 Å. All Ca(1)-Si(1) bond lengths are 3.13 Å. All Ca(1)-Si(2) bond lengths are 3.23 Å. In the second Ca site, Ca(2) is bonded to twelve equivalent Si(2) atoms to form face-sharing CaSi12 cuboctahedra. All Ca(2)-Si(2) bond lengths are 3.15 Å. Mg(1) is bonded to four equivalent Ca(1), two equivalent Si(1), and two equivalent Si(3) atoms to form a mixture of distorted face and edge-sharing MgCa4Si4 tetrahedra. Both Mg(1)-Si(1) bond lengths are 2.68 Å. Both Mg(1)-Si(3) bond lengths are 2.77 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to four equivalent Ca(1), two equivalent Mg(1), and one Si(2) atom. The Si(1)-Si(2) bond length is 2.27 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Ca(2), four equivalent Ca(1), one Si(1), and two equivalent Si(2) atoms. Both Si(2)-Si(2) bond lengths are 2.34 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to three equivalent Ca(1) and six equivalent Mg(1) atoms.