CaAlSiO4OH is Esseneite-derived structured and crystallizes in the orthorhombic P2_12_12_1 space group. Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. Al(1) is bonded to one O(2), one O(5), two equivalent O(1), and two equivalent O(3) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. Si(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-57°. H(1) is bonded in a linear geometry to one O(1) and one O(4) atom. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(1), and one Si(1) atom. In the second O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Al(1), and one H(1) atom. In the third O site, O(2) is bonded to two equivalent Ca(1), one Al(1), and one Si(1) atom to form distorted OCa2AlSi trigonal pyramids that share corners with two equivalent O(2)Ca2AlSi trigonal pyramids, corners with three equivalent O(3)CaAl2Si trigonal pyramids, and  an edgeedge with one O(3)CaAl2Si trigonal pyramid. In the fourth O site, O(3) is bonded to one Ca(1), two equivalent Al(1), and one Si(1) atom to form distorted OCaAl2Si trigonal pyramids that share corners with two equivalent O(3)CaAl2Si trigonal pyramids, corners with three equivalent O(2)Ca2AlSi trigonal pyramids, and  an edgeedge with one O(2)Ca2AlSi trigonal pyramid. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Si(1), and one H(1) atom.
CaAlSiO4OH is Esseneite-derived structured and crystallizes in the orthorhombic P2_12_12_1 space group. Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. The Ca(1)-O(1) bond length is 2.35 Å. The Ca(1)-O(3) bond length is 2.51 Å. There is one shorter (2.45 Å) and one longer (2.53 Å) Ca(1)-O(2) bond length. There is one shorter (2.34 Å) and one longer (2.49 Å) Ca(1)-O(4) bond length. There is one shorter (2.48 Å) and one longer (2.54 Å) Ca(1)-O(5) bond length. Al(1) is bonded to one O(2), one O(5), two equivalent O(1), and two equivalent O(3) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. The Al(1)-O(2) bond length is 1.92 Å. The Al(1)-O(5) bond length is 1.94 Å. There is one shorter (1.85 Å) and one longer (1.87 Å) Al(1)-O(1) bond length. There is one shorter (1.96 Å) and one longer (2.09 Å) Al(1)-O(3) bond length. Si(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-57°. The Si(1)-O(2) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.70 Å. The Si(1)-O(4) bond length is 1.63 Å. The Si(1)-O(5) bond length is 1.66 Å. H(1) is bonded in a linear geometry to one O(1) and one O(4) atom. The H(1)-O(1) bond length is 1.03 Å. The H(1)-O(4) bond length is 1.51 Å. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(1), and one Si(1) atom. In the second O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Al(1), and one H(1) atom. In the third O site, O(2) is bonded to two equivalent Ca(1), one Al(1), and one Si(1) atom to form distorted OCa2AlSi trigonal pyramids that share corners with two equivalent O(2)Ca2AlSi trigonal pyramids, corners with three equivalent O(3)CaAl2Si trigonal pyramids, and  an edgeedge with one O(3)CaAl2Si trigonal pyramid. In the fourth O site, O(3) is bonded to one Ca(1), two equivalent Al(1), and one Si(1) atom to form distorted OCaAl2Si trigonal pyramids that share corners with two equivalent O(3)CaAl2Si trigonal pyramids, corners with three equivalent O(2)Ca2AlSi trigonal pyramids, and  an edgeedge with one O(2)Ca2AlSi trigonal pyramid. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Si(1), and one H(1) atom.