Ca3Si2(H3O5)2 crystallizes in the monoclinic Cc space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(2), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted CaO7 pentagonal bipyramids that share  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), one O(7), and one O(8) atom. In the third Ca site, Ca(3) is bonded in a 6-coordinate geometry to one O(2), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(7), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O7 pentagonal bipyramid and  an edgeedge with one Ca(1)O7 pentagonal bipyramid. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O7 pentagonal bipyramids. There are six inequivalent H sites. In the first H site, H(1) is bonded in a linear geometry to one O(1) and one O(2) atom. In the second H site, H(2) is bonded in a linear geometry to one O(3) and one O(4) atom. In the third H site, H(3) is bonded in a linear geometry to one O(3) and one O(9) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(9) atom. In the fifth H site, H(5) is bonded in a distorted linear geometry to one O(1) and one O(10) atom. In the sixth H site, H(6) 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 in a distorted rectangular see-saw-like geometry to one Ca(2), one Si(1), one H(1), and one H(5) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ca(1), one Ca(3), one Si(2), and one H(1) atom. In the third O site, O(3) is bonded to one Ca(2), one Si(2), one H(2), and one H(3) atom to form distorted corner-sharing OCaSiH2 trigonal pyramids. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one H(2) atom. In the fifth O site, O(5) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom to form OCa3Si tetrahedra that share corners with three equivalent O(7)Ca3Si tetrahedra,  a cornercorner with one O(8)Ca3Si trigonal pyramid, corners with two equivalent O(3)CaSiH2 trigonal pyramids, and  an edgeedge with one O(8)Ca3Si trigonal pyramid. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(3), and one Si(2) atom. In the seventh O site, O(7) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom to form distorted OCa3Si tetrahedra that share corners with three equivalent O(5)Ca3Si tetrahedra,  a cornercorner with one O(3)CaSiH2 trigonal pyramid, and edges with two equivalent O(8)Ca3Si trigonal pyramids. In the eighth O site, O(8) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom to form distorted OCa3Si trigonal pyramids that share  a cornercorner with one O(5)Ca3Si tetrahedra,  a cornercorner with one O(3)CaSiH2 trigonal pyramid,  an edgeedge with one O(5)Ca3Si tetrahedra, and edges with two equivalent O(7)Ca3Si tetrahedra. In the ninth O site, O(9) is bonded in a distorted water-like geometry to one Ca(1), one Ca(3), one H(3), and one H(4) atom. In the tenth O site, O(10) is bonded in a water-like geometry to one H(5) and one H(6) atom.
Ca3Si2(H3O5)2 crystallizes in the monoclinic Cc space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(2), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted CaO7 pentagonal bipyramids that share  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The Ca(1)-O(2) bond length is 2.44 Å. The Ca(1)-O(4) bond length is 2.53 Å. The Ca(1)-O(5) bond length is 2.38 Å. The Ca(1)-O(6) bond length is 2.36 Å. The Ca(1)-O(7) bond length is 2.42 Å. The Ca(1)-O(8) bond length is 2.57 Å. The Ca(1)-O(9) bond length is 2.52 Å. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), one O(7), and one O(8) atom. The Ca(2)-O(1) bond length is 2.37 Å. The Ca(2)-O(3) bond length is 2.34 Å. The Ca(2)-O(5) bond length is 2.34 Å. The Ca(2)-O(7) bond length is 2.38 Å. The Ca(2)-O(8) bond length is 2.44 Å. In the third Ca site, Ca(3) is bonded in a 6-coordinate geometry to one O(2), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The Ca(3)-O(2) bond length is 2.70 Å. The Ca(3)-O(5) bond length is 2.37 Å. The Ca(3)-O(6) bond length is 2.35 Å. The Ca(3)-O(7) bond length is 2.36 Å. The Ca(3)-O(8) bond length is 2.38 Å. The Ca(3)-O(9) bond length is 2.48 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(7), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O7 pentagonal bipyramid and  an edgeedge with one Ca(1)O7 pentagonal bipyramid. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.71 Å. The Si(1)-O(7) bond length is 1.65 Å. The Si(1)-O(8) bond length is 1.64 Å. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O7 pentagonal bipyramids. The Si(2)-O(2) bond length is 1.69 Å. The Si(2)-O(3) bond length is 1.64 Å. The Si(2)-O(5) bond length is 1.65 Å. The Si(2)-O(6) bond length is 1.62 Å. There are six inequivalent H sites. In the first H site, H(1) is bonded in a linear geometry to one O(1) and one O(2) atom. The H(1)-O(1) bond length is 1.54 Å. The H(1)-O(2) bond length is 1.04 Å. In the second H site, H(2) is bonded in a linear geometry to one O(3) and one O(4) atom. The H(2)-O(3) bond length is 1.48 Å. The H(2)-O(4) bond length is 1.05 Å. In the third H site, H(3) is bonded in a linear geometry to one O(3) and one O(9) atom. The H(3)-O(3) bond length is 1.56 Å. The H(3)-O(9) bond length is 1.03 Å. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(9) atom. The H(4)-O(9) bond length is 1.00 Å. In the fifth H site, H(5) is bonded in a distorted linear geometry to one O(1) and one O(10) atom. The H(5)-O(1) bond length is 1.61 Å. The H(5)-O(10) bond length is 1.03 Å. In the sixth H site, H(6) is bonded in a single-bond geometry to one O(10) atom. The H(6)-O(10) bond length is 1.00 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ca(2), one Si(1), one H(1), and one H(5) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ca(1), one Ca(3), one Si(2), and one H(1) atom. In the third O site, O(3) is bonded to one Ca(2), one Si(2), one H(2), and one H(3) atom to form distorted corner-sharing OCaSiH2 trigonal pyramids. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one H(2) atom. In the fifth O site, O(5) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom to form OCa3Si tetrahedra that share corners with three equivalent O(7)Ca3Si tetrahedra,  a cornercorner with one O(8)Ca3Si trigonal pyramid, corners with two equivalent O(3)CaSiH2 trigonal pyramids, and  an edgeedge with one O(8)Ca3Si trigonal pyramid. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(3), and one Si(2) atom. In the seventh O site, O(7) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom to form distorted OCa3Si tetrahedra that share corners with three equivalent O(5)Ca3Si tetrahedra,  a cornercorner with one O(3)CaSiH2 trigonal pyramid, and edges with two equivalent O(8)Ca3Si trigonal pyramids. In the eighth O site, O(8) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom to form distorted OCa3Si trigonal pyramids that share  a cornercorner with one O(5)Ca3Si tetrahedra,  a cornercorner with one O(3)CaSiH2 trigonal pyramid,  an edgeedge with one O(5)Ca3Si tetrahedra, and edges with two equivalent O(7)Ca3Si tetrahedra. In the ninth O site, O(9) is bonded in a distorted water-like geometry to one Ca(1), one Ca(3), one H(3), and one H(4) atom. In the tenth O site, O(10) is bonded in a water-like geometry to one H(5) and one H(6) atom.