MgAl2(Si3O8)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a distorted pentagonal planar geometry to one O(1), one O(13), one O(14), one O(15), and one O(7) atom. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(14), one O(16), one O(2), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(5)O4 tetrahedra, and corners with two equivalent Si(6)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), one O(13), one O(15), and one O(7) atom to form distorted AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(6)O4 tetrahedra, and corners with two equivalent Si(5)O4 tetrahedra. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(10), one O(12), one O(4), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(11), one O(3), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(4), and one O(6) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(12), one O(3), one O(5), and one O(9) atom to form corner-sharing SiO4 tetrahedra. In the fifth Si site, Si(5) is bonded to one O(13), one O(15), one O(2), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the sixth Si site, Si(6) is bonded to one O(1), one O(14), one O(16), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a T-shaped geometry to one Mg(1), one Al(2), and one Si(6) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(5) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Si(4) and one Si(6) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Si(3) and one Si(5) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Al(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Al(1) and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(3) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to one Mg(1), one Al(2), and one Si(5) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(1), and one Si(6) atom. In the fifteenth O site, O(15) is bonded in a distorted T-shaped geometry to one Mg(1), one Al(2), and one Si(5) atom. In the sixteenth O site, O(16) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(6) atom.
MgAl2(Si3O8)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a distorted pentagonal planar geometry to one O(1), one O(13), one O(14), one O(15), and one O(7) atom. The Mg(1)-O(1) bond length is 2.02 Å. The Mg(1)-O(13) bond length is 2.33 Å. The Mg(1)-O(14) bond length is 2.10 Å. The Mg(1)-O(15) bond length is 2.05 Å. The Mg(1)-O(7) bond length is 2.13 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(14), one O(16), one O(2), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(5)O4 tetrahedra, and corners with two equivalent Si(6)O4 tetrahedra. The Al(1)-O(14) bond length is 1.84 Å. The Al(1)-O(16) bond length is 1.74 Å. The Al(1)-O(2) bond length is 1.74 Å. The Al(1)-O(8) bond length is 1.71 Å. In the second Al site, Al(2) is bonded to one O(1), one O(13), one O(15), and one O(7) atom to form distorted AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(6)O4 tetrahedra, and corners with two equivalent Si(5)O4 tetrahedra. The Al(2)-O(1) bond length is 1.77 Å. The Al(2)-O(13) bond length is 1.72 Å. The Al(2)-O(15) bond length is 1.77 Å. The Al(2)-O(7) bond length is 1.80 Å. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(10), one O(12), one O(4), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. The Si(1)-O(10) bond length is 1.62 Å. The Si(1)-O(12) bond length is 1.62 Å. The Si(1)-O(4) bond length is 1.63 Å. The Si(1)-O(7) bond length is 1.66 Å. In the second Si site, Si(2) is bonded to one O(11), one O(3), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. The Si(2)-O(11) bond length is 1.65 Å. The Si(2)-O(3) bond length is 1.64 Å. The Si(2)-O(8) bond length is 1.58 Å. The Si(2)-O(9) bond length is 1.65 Å. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(4), and one O(6) atom to form corner-sharing SiO4 tetrahedra. The Si(3)-O(10) bond length is 1.63 Å. The Si(3)-O(11) bond length is 1.62 Å. The Si(3)-O(4) bond length is 1.64 Å. The Si(3)-O(6) bond length is 1.64 Å. In the fourth Si site, Si(4) is bonded to one O(12), one O(3), one O(5), and one O(9) atom to form corner-sharing SiO4 tetrahedra. The Si(4)-O(12) bond length is 1.63 Å. The Si(4)-O(3) bond length is 1.62 Å. The Si(4)-O(5) bond length is 1.62 Å. The Si(4)-O(9) bond length is 1.63 Å. In the fifth Si site, Si(5) is bonded to one O(13), one O(15), one O(2), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. The Si(5)-O(13) bond length is 1.65 Å. The Si(5)-O(15) bond length is 1.69 Å. The Si(5)-O(2) bond length is 1.59 Å. The Si(5)-O(6) bond length is 1.64 Å. In the sixth Si site, Si(6) is bonded to one O(1), one O(14), one O(16), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. The Si(6)-O(1) bond length is 1.67 Å. The Si(6)-O(14) bond length is 1.67 Å. The Si(6)-O(16) bond length is 1.58 Å. The Si(6)-O(5) bond length is 1.62 Å. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a T-shaped geometry to one Mg(1), one Al(2), and one Si(6) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(5) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Si(4) and one Si(6) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Si(3) and one Si(5) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Al(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Al(1) and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(3) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to one Mg(1), one Al(2), and one Si(5) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(1), and one Si(6) atom. In the fifteenth O site, O(15) is bonded in a distorted T-shaped geometry to one Mg(1), one Al(2), and one Si(5) atom. In the sixteenth O site, O(16) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(6) atom.