Ca2FeAl2Si3O12(OH) crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(5), one O(7), two equivalent O(1), and two equivalent O(3) atoms. In the second Ca site, Ca(2) is bonded in a 10-coordinate geometry to one O(10), one O(7), two equivalent O(3), two equivalent O(8), and four equivalent O(2) atoms. Fe(1) is bonded to one O(4), one O(8), two equivalent O(1), and two equivalent O(2) atoms to form FeO6 octahedra that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Al(1)O6 octahedra. In the second Al site, Al(2) is bonded to two equivalent O(10), two equivalent O(3), and two equivalent O(6) atoms to form AlO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and edges with two equivalent Al(2)O6 octahedra. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(7), one O(9), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-56°. In the second Si site, Si(2) is bonded to one O(8), one O(9), and two equivalent O(3) atoms to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 37-54°. In the third Si site, Si(3) is bonded to one O(5), one O(6), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, and corners with two equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. H(1) is bonded in a single-bond geometry to one O(10) atom. There are ten inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Fe(1), one Al(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCaAlFeSi tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(2), one Fe(1), and one Si(3) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(2), and one Si(2) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Fe(1) and two equivalent Al(1) atoms. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Al(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Al(2) and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ca(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to two equivalent Ca(2), one Fe(1), and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Ca(2), two equivalent Al(2), and one H(1) atom.
Ca2FeAl2Si3O12(OH) crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(5), one O(7), two equivalent O(1), and two equivalent O(3) atoms. The Ca(1)-O(5) bond length is 2.61 Å. The Ca(1)-O(7) bond length is 2.32 Å. Both Ca(1)-O(1) bond lengths are 2.48 Å. Both Ca(1)-O(3) bond lengths are 2.34 Å. In the second Ca site, Ca(2) is bonded in a 10-coordinate geometry to one O(10), one O(7), two equivalent O(3), two equivalent O(8), and four equivalent O(2) atoms. The Ca(2)-O(10) bond length is 2.54 Å. The Ca(2)-O(7) bond length is 2.26 Å. Both Ca(2)-O(3) bond lengths are 2.70 Å. Both Ca(2)-O(8) bond lengths are 3.05 Å. There are two shorter (2.55 Å) and two longer (2.83 Å) Ca(2)-O(2) bond lengths. Fe(1) is bonded to one O(4), one O(8), two equivalent O(1), and two equivalent O(2) atoms to form FeO6 octahedra that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. The Fe(1)-O(4) bond length is 1.97 Å. The Fe(1)-O(8) bond length is 1.91 Å. Both Fe(1)-O(1) bond lengths are 2.27 Å. Both Fe(1)-O(2) bond lengths are 2.03 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Al(1)O6 octahedra. Both Al(1)-O(1) bond lengths are 1.96 Å. Both Al(1)-O(4) bond lengths are 1.86 Å. Both Al(1)-O(5) bond lengths are 1.99 Å. In the second Al site, Al(2) is bonded to two equivalent O(10), two equivalent O(3), and two equivalent O(6) atoms to form AlO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and edges with two equivalent Al(2)O6 octahedra. Both Al(2)-O(10) bond lengths are 1.89 Å. Both Al(2)-O(3) bond lengths are 1.87 Å. Both Al(2)-O(6) bond lengths are 1.95 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(7), one O(9), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-56°. The Si(1)-O(7) bond length is 1.59 Å. The Si(1)-O(9) bond length is 1.66 Å. Both Si(1)-O(1) bond lengths are 1.67 Å. In the second Si site, Si(2) is bonded to one O(8), one O(9), and two equivalent O(3) atoms to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 37-54°. The Si(2)-O(8) bond length is 1.61 Å. The Si(2)-O(9) bond length is 1.65 Å. Both Si(2)-O(3) bond lengths are 1.64 Å. In the third Si site, Si(3) is bonded to one O(5), one O(6), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, and corners with two equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. The Si(3)-O(5) bond length is 1.69 Å. The Si(3)-O(6) bond length is 1.66 Å. Both Si(3)-O(2) bond lengths are 1.65 Å. H(1) is bonded in a single-bond geometry to one O(10) atom. The H(1)-O(10) bond length is 0.99 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Fe(1), one Al(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OCaAlFeSi tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Ca(2), one Fe(1), and one Si(3) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Al(2), and one Si(2) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Fe(1) and two equivalent Al(1) atoms. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Al(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Al(2) and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ca(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to two equivalent Ca(2), one Fe(1), and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Ca(2), two equivalent Al(2), and one H(1) atom.