The origin and formation of clay minerals in alpine soils

Clay minerals are among the most chemically active components and are a bridge between the inorganic and organic parts of a soil. The clay minerals influence pedogenetic processes by interacting with cations and inorganic and organic compounds, influencing the nutrition of the plants and the structure of the soils. Clay minerals are phyllosilicates and can in soils be either inherited from the parent material, neoformed, or transformed from precursor minerals. Relatively shortly after exposure of the parent material to atmospheric conditions, important mineral transformation reactions can occur, even in cold alpine climates. In alpine environments, the soil system reacts in a particularly sensitive way at the beginning of soil formation, i.e. during the first c. 3000 years. With time, the formation and transformation rates, and thus changes, decelerate. Smectitic components, and therefore 2:1 mineral structures, are the weathering steady-state products. Although weathering conditions are particularly intense close to the timberline and on pole-facing sites, 2:1 minerals strongly prevail over kaolinite or gibbsite, which are most often encountered as a weathering steady-state product in tropical regions. Smectitic components enrich under conditions of high percolation rates, cool climates (close to the treeline), high amounts of organic ligands, low erosion, stable conditions, and thus low soil production rates. Smectite formation therefore relates not only to the paradigms of the percolation theory, but the type and presence of vegetation and the production of organic ligands are additional driving factors