Nuovi dati sulla dietrichite di Boccheggiano, Grosseto

During the reinvestigation of sulfate specimens at the Mineralogical Museum of the University of Rome "La Sapienza", a specimen classified as “halotrichite”, from the now closed pyrite mine of Boccheggiano (Grosseto), which is not hygroscopic unlike the other halotrichite specimens, has been identified as dietrichite. Unlike all previously studied dietrichite, the mineral we investigated is very close to the ideal chemical composition. In fact, its chemical composition, determined by means of ICP and thermogravimetric analyses, is (Zn0,93Fe0,07)Al2(SO4)4 · 22H2O. Dietrichite of this specimen forms both sub-millimetric whitish acicular crystals and white concretions. Crystals are prismatic and sometimes form parallel bundles, showing a spiral bending. The structure refinement has been performed by using Rietveld method on the collected powder diffraction data. Structure data confirm that dietrichite is isostructural with apjohnite and pickeringite.