NaCa2Fe5(SiO3)8 is Esseneite-derived structured and crystallizes in the monoclinic C2/m space group. Na(1) is bonded in a linear geometry to two equivalent O(7) atoms. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, and edges with two equivalent Fe(1)O6 octahedra. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one Fe(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-63°. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-60°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Fe(3), and one Si(1) atom. In the second O site, O(2) is bonded to one Ca(1), one Fe(1), one Fe(2), and one Si(2) atom to form a mixture of distorted edge and corner-sharing OCaFe2Si trigonal pyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(3) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ca(1), one Fe(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Na(1) and two equivalent Si(1) atoms.
NaCa2Fe5(SiO3)8 is Esseneite-derived structured and crystallizes in the monoclinic C2/m space group. Na(1) is bonded in a linear geometry to two equivalent O(7) atoms. Both Na(1)-O(7) bond lengths are 2.53 Å. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. Both Ca(1)-O(2) bond lengths are 2.40 Å. Both Ca(1)-O(4) bond lengths are 2.33 Å. Both Ca(1)-O(5) bond lengths are 2.85 Å. Both Ca(1)-O(6) bond lengths are 2.68 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. Both Fe(1)-O(1) bond lengths are 2.13 Å. Both Fe(1)-O(2) bond lengths are 2.26 Å. Both Fe(1)-O(3) bond lengths are 1.99 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, and edges with two equivalent Fe(1)O6 octahedra. Both Fe(2)-O(1) bond lengths are 2.16 Å. Both Fe(2)-O(2) bond lengths are 2.19 Å. Both Fe(2)-O(4) bond lengths are 2.09 Å. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. Both Fe(3)-O(3) bond lengths are 2.04 Å. All Fe(3)-O(1) bond lengths are 2.19 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one Fe(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-63°. The Si(1)-O(1) bond length is 1.61 Å. The Si(1)-O(5) bond length is 1.66 Å. The Si(1)-O(6) bond length is 1.66 Å. The Si(1)-O(7) bond length is 1.66 Å. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-60°. The Si(2)-O(2) bond length is 1.63 Å. The Si(2)-O(4) bond length is 1.61 Å. The Si(2)-O(5) bond length is 1.69 Å. The Si(2)-O(6) bond length is 1.70 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Fe(3), and one Si(1) atom. In the second O site, O(2) is bonded to one Ca(1), one Fe(1), one Fe(2), and one Si(2) atom to form a mixture of distorted edge and corner-sharing OCaFe2Si trigonal pyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(3) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ca(1), one Fe(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Na(1) and two equivalent Si(1) atoms.