This project will investigate the origin of aluminous Martian clay minerals (thought to be Hesperian in age) as possibly generated by acid hydrous alteration of silicate rocks. Clays are abundant on Mars, indicating extensive and continued hydrous activity at an early stage in the planet. Such fact has implications for the search of evidence for extraterrestrial life and for our knowledge of past Martian climate and conditions.Aluminous clay formations on Mars typically contain kaolinite, montmorillonite, beidellite, hydrous silica and, frequently, sulphates. By comparison with Earth environments, this mineral assemblage suggests that it formed by acid alteration of silicate rocks, possibly basalt or the more ancient Fe- and Mg-rich clays that are frequently overlain by the aluminous clays. This project will use Al-rich clay assemblages in acid-altered rocks in Rio Tinto (Spain) as a proxy for the similar mineral assemblages on Mars.Samples from Rio Tinto will be used to determine the intensity and mode of acid alteration. The crystal-chemistry of the clay minerals will be characterized in detail using advanced microscopy, chemical, spectroscopic, structural and isotope analytical techniques. They will be also investigated using diffuse reflectance near-infrared spectroscopy and their spectra compared with those obtained by remote sensing on Mars. X-ray diffraction and chemical data can be used also for comparison with those of clays on Mars in future rover missions.This study will (1) produce new results that will constrain the mineralogy and formation conditions of aluminous clays on Mars; (2) increase the spectral library for Mars studies with well-characterized, complex clays; (3) enhance the European profile in planetary studies; and (4) provide the fellow with new, advanced skills in mineralogy and analytical techniques that will prepare him for new opportunities and a sustained research career in Europe.