The crystal structure of strunzite, a contribution to the crystal chemistry of basic ferric-manganous hydrated phosphates

Abstract

Strunzite, MnFe2(PO4)2(OH)2·6H2O, is triclinic space groupPĪ,Z=2; lattice parameters area=10.228,b=9.837,c=7.284 A, α=90.17, β=98.44, γ=117.44°. The mineral exhibits a well marked monoclinic pseudocell with the pseudosymmetry ofC2/c space group. The crystal structure was solved by Patterson and Fourier methods and refined by least-squares method. FinalR index is 0.095 for 1565 observed reflections. The atomic arrangement of strunzite is related to that of metavauxite and those of laueite, pseudolaueite and stewartite. It consists of chains built up by Fe coordination octahedra sharing vertices; PO4 tetrahedra link together adjacent octahedra. Parallel chains are connectedvia PO4 groups to form thick slabs. Parallel slabs are connected by Mn coordination octahedra, to form the three-dimensional framework. Strunzite, according toMoore's stereoisomeric notation, can be assigned the structural formula: $$Mn^{2 + } (H_2 O)_4 (Op)_{2 trans} [Fe^{3 + } (OH) (H_2 O) (Op)_{3 III c} ]_2 P_2 .$$