Search

This work relates to the occurrence and crystal-chemical characterization of fibrous erionite, a carcinogenic zeolite, discovered for the first time in the volcanic rocks of Latium, Italy. The erionite samples were investigated using SEM, TGA, PXRD, FTIR and Raman spectroscopies. Cell parameters, fractional coordinates and site scattering were refined using the Rietveld method. Two different types of erionite were found, having different crystal morphologies, chemical composition, and structure. The first type is an extremely fibrous erionite-K, with Si/(Si+Al) ratio of 0.77, cell parameters a=13.255 Å, c=15.053 Å and cell volume V=2290.49 Å3. The second type is acicular to highly fibrous erionite-Na, with a lower Si/(Si+Al) ratio (0.72-0.73) and larger cell parameters (a=13.291 Å, c=15.146 Å, cell volume V=2317.35 Å3). Both erionite types occur as fibers of inhalable size. The structure of both samples, refined by the Rietveld method on powder X-ray diffraction data, collected in transmission mode on capillaries, is consistent with that of samples with similar extra-framework cations content. Raman and FTIR data are presented and discussed. The described finding of potentially carcinogenic erionite in the volcanic rocks of Latium that are typically rich in zeolites of various nature, both as cavity filling and devitrification products of glass, suggests that this hazardous mineral might be more common than previously believed in the area and points to the need for detailed and more systematic studies., Periodico di Mineralogia, Vol. 92 No. 2 (2023)

This opening paper introduces the contributions of this special issue on mineral fibres and reports a gallery of the major results accomplished within the multidisciplinary project PRIN (PROGETTI DI RICERCA DI RILEVANTE INTERESSE NAZIONALE) 2017 “FIBRES: a multidisciplinary mineralogical, crystal-chemical and biological project to amend the paradigm of toxicity and cancerogenicity of mineral fibres” by the six different Research Units from the Universities of Ancona, Genova, Modena, Rome, Pisa-Parma, and Urbino. The main goal of the project was to increase the knowledge of the mechanisms by which mineral fibres, with special attention to asbestos and fibrous erionite, prompt adverse effects in vivo, linking the fibres’ crystal-chemical-physical parameters to their toxicity/carcinogenicity potential and recasting the existing mechanistic ‘fibre toxicity paradigms’. This special issue contains specific contributions from each Research Unit of the project. The implications of the findings of the project are beyond the advance of the knowledge in the world of mineralogy/crystallography and constitute a remarkable progress in the understanding of the biological activity of mineral fibres in vivo., Periodico di Mineralogia, Vol. 92 No. 2 (2023)

The properties of rocks are determined from the physical properties of minerals composing the rock, which in turn ultimately depend on the crystal phonon modes and electron density of states. Amphiboles (AB2C5T8O22W2, C5 = M12M22M3) are among the major hydrous-silicate mineral constituents of the lithosphere, whose structure consists of strips of 6-membered TO4-rings attached to MO6 octahedra. To elucidate the atomistic origin of the rock conductivity observed in peculiar geological settings, we have studied single crystals of MFe-containing amphiboles from different subgroups by in situ high-temperature polarized Raman spectroscopy and density-functional-theory calculations of the electron band structure of grunerite (A¨Fe2+2Fe2+5Si8O22(OH)2) as a model pure-MFe2+ amphibole [1]. Above a certain temperature resonance Raman scattering occurs, due to the formation of small polarons arising from the coupling between polar optical phonons and electron transitions within Fe2+O6 octahedra, the mobility of which through the mineral bulk is strongly anisotropic. The FeO6-related polarons coexist with delocalized H+, that is, at elevated temperatures typical of lithosphere Fe-bearing amphiboles are conductive and exhibiting two types of charge carriers: electronic polarons and H+ cations, regardless of the oxygen fugacity. However, the presence of external oxygen favours the ejection of H+ and electrons from the crystal. Therefore, at lithospheric temperatures Fe2+-bearing amphiboles can be in a unique metastable state with an anisotropic surface-to-bulk gradient in the chemical potential. Same phenomena are expected for other rock-forming minerals sharing a similar structural feature with amphiboles: linked TO4-rings and MO6-octahedra. [1] Mihailova et al. Commun. Mater. 2, 57/1-10 (2021)