The compound described by MgAl2(Si3O8)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a distorted see-saw-like geometry to one O(13), one O(16), one O(2), and one O(5) 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 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 linear geometry to one Al(2) and one Si(6) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), 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 linear geometry to one Si(1) and one Si(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), 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 bent 120 degrees geometry to one Al(2) and one Si(1) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees 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 linear geometry to one Si(1) and one Si(4) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar 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 bent 150 degrees geometry to one Al(1) and one Si(6) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(5) atom. In the sixteenth O site, O(16) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(1), and one Si(6) atom. is represented by the CIF file [CIF]
data_MgAl2(Si3O8)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.084
_cell_length_b   8.929
_cell_length_c   8.650
_cell_angle_alpha   91.226
_cell_angle_beta   91.549
_cell_angle_gamma   90.657
_symmetry_Int_Tables_number   1
_cell_volume   392.406
_cell_formula_units_Z   1
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Mg  Mg0  1  0.139  0.114  0.471  1.0
  Al  Al1  1  0.628  0.316  0.316  1.0
  Al  Al2  1  0.885  0.167  0.812  1.0
  Si  Si3  1  0.916  0.822  0.812  1.0
  Si  Si4  1  0.573  0.680  0.323  1.0
  Si  Si5  1  0.426  0.673  0.665  1.0
  Si  Si6  1  0.078  0.827  0.177  1.0
  Si  Si7  1  0.406  0.319  0.659  1.0
  Si  Si8  1  0.132  0.171  0.165  1.0
  O  O9  1  0.989  0.167  0.002  1.0
  O  O10  1  0.483  0.245  0.488  1.0
  O  O11  1  0.325  0.715  0.204  1.0
  O  O12  1  0.174  0.766  0.722  1.0
  O  O13  1  0.169  0.997  0.246  1.0
  O  O14  1  0.346  0.497  0.649  1.0
  O  O15  1  0.833  0.982  0.743  1.0
  O  O16  1  0.651  0.508  0.321  1.0
  O  O17  1  0.826  0.784  0.279  1.0
  O  O18  1  0.676  0.699  0.784  1.0
  O  O19  1  0.491  0.740  0.495  1.0
  O  O20  1  0.994  0.831  0.997  1.0
  O  O21  1  0.126  0.223  0.676  1.0
  O  O22  1  0.418  0.246  0.170  1.0
  O  O23  1  0.619  0.284  0.791  1.0
  O  O24  1  0.947  0.235  0.309  1.0
[/CIF]
.
The compound described by MgAl2(Si3O8)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a distorted see-saw-like geometry to one O(13), one O(16), one O(2), and one O(5) 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 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 linear geometry to one Al(2) and one Si(6) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), 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 linear geometry to one Si(1) and one Si(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), 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 bent 120 degrees geometry to one Al(2) and one Si(1) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees 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 linear geometry to one Si(1) and one Si(4) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar 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 bent 150 degrees geometry to one Al(1) and one Si(6) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(5) atom. In the sixteenth O site, O(16) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(1), and one Si(6) atom. is represented by the CIF file [CIF]
data_MgAl2(Si3O8)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.084
_cell_length_b   8.929
_cell_length_c   8.650
_cell_angle_alpha   91.226
_cell_angle_beta   91.549
_cell_angle_gamma   90.657
_symmetry_Int_Tables_number   1
_cell_volume   392.406
_cell_formula_units_Z   1
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Mg  Mg0  1  0.139  0.114  0.471  1.0
  Al  Al1  1  0.628  0.316  0.316  1.0
  Al  Al2  1  0.885  0.167  0.812  1.0
  Si  Si3  1  0.916  0.822  0.812  1.0
  Si  Si4  1  0.573  0.680  0.323  1.0
  Si  Si5  1  0.426  0.673  0.665  1.0
  Si  Si6  1  0.078  0.827  0.177  1.0
  Si  Si7  1  0.406  0.319  0.659  1.0
  Si  Si8  1  0.132  0.171  0.165  1.0
  O  O9  1  0.989  0.167  0.002  1.0
  O  O10  1  0.483  0.245  0.488  1.0
  O  O11  1  0.325  0.715  0.204  1.0
  O  O12  1  0.174  0.766  0.722  1.0
  O  O13  1  0.169  0.997  0.246  1.0
  O  O14  1  0.346  0.497  0.649  1.0
  O  O15  1  0.833  0.982  0.743  1.0
  O  O16  1  0.651  0.508  0.321  1.0
  O  O17  1  0.826  0.784  0.279  1.0
  O  O18  1  0.676  0.699  0.784  1.0
  O  O19  1  0.491  0.740  0.495  1.0
  O  O20  1  0.994  0.831  0.997  1.0
  O  O21  1  0.126  0.223  0.676  1.0
  O  O22  1  0.418  0.246  0.170  1.0
  O  O23  1  0.619  0.284  0.791  1.0
  O  O24  1  0.947  0.235  0.309  1.0
[/CIF]
.