We investigated the oxidation behaviour of a synthetic potassic-ferro-richterite up to 750 °C by using simultaneous X-ray absorption spectroscopy and X-ray diffraction experiments with synchrotron radiation. From the X-ray diffraction results, we observed an abrupt decrease of cell dimensions at ∼335 °C accompanied by an anomalous increase in the monoclinic cell angle β. From the analysis of the XANES spectra at the iron K-edge, we observed that the structural shrinkage is due to the iron oxidation process, coupled to hydrogen loss, occurring at ∼315 °C, slightly before the cell contraction. Combining these results with previous studies performed on similar samples by single-crystal structure refinement, Mössbauer, high temperature-Fourier transform IR and Raman spectroscopies, we show that the temperature evolution in Fe-amphiboles is a multi-step process. Following the iron oxidation driven by temperature, the structural dynamics in this double-chain silicate is ruled by local strains in the ribbon of iron-filled octahedra, mainly due to the contraction of the M(1) site.

The EuPRAXIA EU project is at the forefront of advancing particle accelerator research and the development of photon sources through innovative plasma acceleration approaches. Within this framework, the EuAPS project aims to exploit laser wakefield acceleration to build and operate a betatron radiation source at the INFN Frascati National Laboratory. The EuAPS source will provide femtosecond X-ray pulses in the spectral region between about 1 and 10 keV, unlocking a realm of experimental ultrafast methodologies encompassing diverse imaging and X-ray spectroscopy techniques. This paper presents a description of the EuAPS betatron source, including simulations of the photon beam parameters, outlines the preliminary design of the dedicated photon beamline, and provides an insightful overview of its photon science applications.

Opals and cryptocrystalline silica may be found in a very broad range of geological environments (Chauviré et al., 2017), systematically related to the availability of an aqueous fluid. Due to its conditions of formations, opal may contain abundant H2O, CO2 or both (Sodo et al., 2017), and the presence of these molecules may provide information of their genetic context. In this work we studied a series of samples from the volcanic region of Allumiere-Tolfa, north of Rome (Latium, Italy). This district has a Pliocene-Pleistocene age and is related to the Tuscan acid volcanism. It shows a very intense late-stage hydrothermal alteration that gave rise to two distinct ore basins: one to the south of the Allumiere town, consisting of sulfide (Pb, Fe, Zn, Hg) and Fe-oxide mineralizations, and a second, to the north, mainly consisting of alunite and kaolin. Both ore deposits were intensely exploited during the medieval to recent period. The hydrothermal alteration giving rise to the sulfate and clay deposits is also associated with a pervasive deposition, within the early volcanics, of opaline or microcrystalline silica, consisting of mineral replacements, veins and formation of agate druses. Although the sulphide-sulfate and clay products have been studied, due to their interest as georesources, and relevant petrological, geochemical and isotopic data can be found in the oldest literature (Lombardi and Sheppard, 1977), the silica mineralizations have never been addressed. We studied here a series of samples occurring as vein depositions or as banded crystallizations from different areas in the volcanic district. The samples were examined by using a combination of XRD, SEM-EDS and FTIR + Raman imaging. Opaline silica with different degree of order, from opal AN (hyalite) to opal A to opal CT, was identified. Some samples contain CO2 besides H2O/OH. The banded agates were found to consist of a layering of micro-crystalline and fibrous quartz (chalcedony) with different water contents, interbedded with moganite-rich layers; moganite, in particular was found to be associated to lower H2O contents. The 18O and D/H isotopic data of Lombardi and Sheppard (1977) indicate temperatures around 120-100°C for the hydrothermal process responsible for the hydrothermal deposits, in close agreement with the typical range of T for the formation of opaline silica (Heaney, 1993). The ore forming process can be thus interpreted following the classical model of hydrothermal/metasomatic phenomena at low-depth, accompanied by extensive alteration of the pre-existing rocks, due to mixed magmatic/meteoric fluids, with the formation of kaolinite + alunite + sulfates + silica (Hedenquist et al., 2000). ReferencesChauviré, B., Rondeau, B., Mangold, N. (2017) Eur. J. Miner. 29, 409-421Heaney, P.J. (1993) Contrib. Mineral. Petrol., 115, 66-74.Hedenquist, J.W., Arribas, A.R., Gonzalez-Urien, E. (2000) SEG Reviews, 13, 245-277.Lombardi, G. and Sheppard, S.M.F., (1977) Clay Miner., 12, 147-161.Sodo, A., Casanova Municchia, A., Barucca, S., Bellatreccia, F., Della Ventura, G., Butini, F., Ricci M.A. (2016) J. Raman Spec. 47, 1444-1451.