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International audience; We report the results of a rock magnetic and archeointensity study on pottery fragments recovered at the archaeological site of Puertas de Rolón, Capacha culture (Colima), that is considered one of the most important pre-Classic cultural developments of western Mesoamerica, Mexico. Standard rock magnetic experiments were carried out in order to investigate the reliability of the ancient field strength recovered from studied materials. Six out of the seven analyzed fragments gave reliable intensity determinations. The mean archeointensity value obtained in this study is 35.3 ± 3.4 μT. It is in good agreement with another contemporaneous Mesoamerican mean archeointensity of 34.3 ± 1.1 μT obtained for El Opeño. Statistically similar rock-magnetic parameters between ceramics from El Opeño and Puertas de Rolón potsherds appear to be related to clay-sources with similar geological settings and weathering processes. Alternatively, ancient trade or interexchange between western (Capacha Culture) and eastern Mesoamerica locations, as it has been proposed earlier, seem to be supported by results obtained in this study.

We present a diagnostic study to evaluate the suitability of Ficus benjamina tree leaves as a captor of heavy metal particles from atmospheric dusts in urban areas. Leaf samples were taken at 16 localities within three areas in Morelia, state of Michoacan (Mexico’s medium size city, 830000 inhabitants). Measurements of magnetic susceptibility were conducted to determine the magnetic enhancement using samples from green, relatively unpolluted area, as a reference. The samples collected at areas with heavy traffic (main avenues) yielded values almost ten times higher than the values obtained for the unpolluted reference. Isothermal Remanent Magnetization curves are proportional to the degree of pollution. Associations of almost pure magnetite with heavy metals were revealed by scanning electron microscope.

International audience; The oxidation state of vanadium in natural and synthetic Fe-Ti oxides is determined using high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS). Eleven natural magnetite-bearing samples from a borehole of the Main Magnetite Layer of the Bushveld Complex (South Africa), five synthetic Fe oxide samples, and three natural hematite-bearing samples from Dharwar supergroup (India) are investigated. V K edge spectra were recorded on the ID26 beamline at the European Synchrotron Radiation Facility (Grenoble, France), and the pre-edge features were used to determine the local environment and oxidation state of vanadium. In the case of the magnetite samples (natural and synthetic), we show that vanadium is incorporated in the octahedral site of the spinel structure under two oxidation states: ?III and ?IV. The variations of the pre-edge area are interpreted as various proportions in V3? and V4? (between 9.5 and 16.3% of V4?), V3? being the main oxidation state. In particular, the variations of the V4?/V3? ratio along the profile of the Main Magnetite Layer seem to follow the crystallization sequence of the layer. In the case of the hematite samples from India, the pre-edge features indicate that vanadium is substituted to Fe and mainly incorporated as V4? (between 40 and 72% of V4?). We also demonstrate the potentiality of HERFD-XAS for mineralogical studies, since it can filter out the unwanted fluorescence and give better resolved spectra than conventional XAS