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This work is aimed at the crystal chemical and structural characterization of micas from Colli Albani volcano. In particular all the samples considered in this study, with the exception of sample CC, are from the ending volcanic sequences, usually referred as Albano maar lake. Micas from the first three phreatomagmatic units are homogeneous in composition or show well defined chemical trends. From the forth phreatomagmatic unit upward, chemical composition is more variable, especially in the ejecta. The Fe/(Fe+Mg) ratio varies from 0.06 to 0.55, thus the mica chemical composition ranges from phlogopite to magnesian annite through ferroan phlogopite. Heterovalent octahedral substitutions are related to Ti, Al and very limited amount of Cr. In the interlayer Ba for K substitutions occur up to 0.06 apfu. Crystal structure refinement were carried out in the space group C2/m and C2/c for 1M and 2M1 polytype, respectively (agreement factor, Robs: 0.021 ≤ Robs ≤ 0.035). The crystal structure of micas studied appears to be mostly affected by annitic substitution. An increase in the annitic component of the mica is reflected by a decrease in the distortion affecting both individual tetrahedra (tetrahedral angle variance, TAV: 0.49 ≤ TAV ≤ 1.13°2) and the tetrahedral ring (6.59 ≤ α ≤ 10.34°). Interlayer topology was found to be affected as well. A very well established correlation can be defined between Fe and Ti content and thus an effect of Ti content over the interlayer topology may be introduced also. The deprotonation of the anionic site was found in literature to be a powerful petrogenetic indicator. A well established correlation was found between heterovalent octahedral substitution and anionic site deprotonation. On the contrary heterovalent interlayer substitutions are accompanied by F- for (OH)- substitution.

The effect of cysteine on the adsorption of Cd(II) by kaolinite was examined at 25°C using a low-defect kaolinite from Minas Gerais (Brazil) and a high-defect kaolinite from Berici Hills (Italy). The chemical data demonstrated that the amount of Cd–cysteine detected on kaolinite increases rapidly during the first few hours with a first-order reaction, thereafter adsorption becomes linear with time for low-defect kaolinite and slows rapidly for high-defect kaolinite. In low-ordered kaolinite, the Cd–cysteine is intercalated in the structure. Evidence of these changes was also observed by differential thermal analysis (DTA). The thermal decomposition of the Cd–cysteine adsorbed on the kaolinites was studied by analysing the evolved gases. The mass spectra of both samples show the evolution of NO (or CH3CH3, m/z = 30), CO2 (m/z = 44), and SO2 (m/z = 64) between 150 and 300°C and of H2O (m/z = 18), CO2 (m/z = 44) and SO2 (m/z = 64) in the temperature range between 400 and 700°C. The high-defect kaolinite also caused the evolution of molecular units with m/z=34 (H2S) and m/z=76 (N2O3).

Geochemical processes that result in the reduction of hexavalent chromium in natural waters with pyrite (FeS 2) have been studied at varying degrees of pH (from 1.2 to 12.6) and solution concentration (from 0.001 to 0.3 M of Cr(VI) in order to demonstrate the differences in the proportions of elements between the aqueous and solid phases and to infer mechanisms that limit the Cr(VI) concentration in pore-waters in iron sulphide-rich environments. The experiments were carried out in the absence of oxygen and on pyrite grains previously treated to remove any oxide or sulphur layer at the mineral surface. The methods used to characterize reacting solutions and mineral surface comprised: chemical analyses (microprobe analyses and inductively coupled plasma analyses), scanning electron microscopy, atomic force microscopy and X-ray single crystal analysis. The results suggest that: 1) mineral dissolution increases with decreasing pH, whereas it is close to zero at pH > 7; at alkaline pH, the Cr(VI) reduction is very low and the decrease in total Cr probably indicates the formation of precipitated phases, like FeCrO 4, on the pyrite surface; 2) Cr(VI) reduction is significant at pH < 2.3. Cr(VI) to Cr(III) reduction involves the oxidation of Fe(II) and S 2- 2 on the pyrite surfaces, following the reaction surfaces.