Tuhualite crystal structure.

As judged by crystal structure analysis, the crystallochemical formula of tuhualite is (Na,K)(2)(VI) (Fe(+3))(2)(VI) (Fe(+2))(2)(VI) Si(12)O(30) . H(2)O, with four such formulas in the unit cell. The structure is characterized by six-repeat double chains of silicon tetrahedrons and chains of edge-sharing, alternating iron tetrahedrons and octahedrons. Chains of each kind are connected by corner sharing to four chains of the other type. The iron cations appear to be anomalously ordered with Fe(+2) in tetrahedral and Fe(+3) in octahedral sites.