This project aims at assessing the influence of microbial activity and water chemistry on the formation of clay. Clays are the natural product of the chemical weathering of silicate rocks at the lithosphere-hydrosphere-atmosphere contact. They interact greatly with water, air (they are transported long distances by the wind) and living organisms, especially those taking their nutrients directly from the soil. As a result, they are very important in all natural processes and human activities.Our knowledge of the inorganic processes producing clays is still incomplete. In addition, biological processes contribute significantly to the production of clays. It is necessary to study the effect of biological activity on the formation of clays in order to understand clay processes fully and, more generally, the geochemical cycles at the Earth’s surface.The project will study the combined influence of water chemistry and microbial activity on the rate of clay formation and the type of clay produced. Volcanic glass will be reacted with 4 types of natural water: spring water, freshwater, seawater and hypersaline water. The experiments will be carried out with and without microbial activity (the microbial activity will be that originally present in the natural water). During the experiments, the microbial activity (molecular methods) and the water chemistry will be monitored. After the experiments, the reaction products will be investigated using SEM, TEM, micro-infrared and micro-X-ray diffraction. The study will provide the following information: 1) relative and combined influence of water chemistry and microbiological activity on clay formation rate and clay chemistry; 2) relative influence of water and rock chemistry in controlling the composition of the clay formed; 3) interaction between the microorganisms and the volcanic glass and neoformed clay; 4) identity and development of the microbial populations.