CRYSTALLOCHEMICAL FEATURES OF Ti- AND Sb-RICH NEZILOVITE

A variety of the mineral nezilovite, containing antimony and an elevated amount of titanium, has been studied using microprobe and X-ray diffraction analysis. The diffraction experiment was performed on a crystal presenting an aggregate of nezilovite and högbomite with close unit-cell parameters. The parameters of the hexagonal cell of the nezilovite studied are a = 5.8855(2) Å, c = 23.092(1) Å, V = 692.73 (4) Å3,sp. gr. P6₃/mmc. The structural model is refined using a limited number of unique reflections 231F > 4σ(F) to R = 0.08. The crystallochemical formula is (Z = 2) PbZn2(Ti0.9Al0.1)(Al0.6Sb )Mn Fe O18.5(O,OH)0.5. The distribution of cations of this composition over structure sites is established. A basis of the mineral structure is a set of spinel layers, consisting of edge-sharing Fe³⁺ octahedra. They alternate with two heteropolyhedral layers: Zn tetrahedra combine (Al,Sb) octahedra in one layer, and five-vertex Ti polyhedra combine dimers of Mn³⁺ octahedra in the other layer.