argillization

Argillization is a geological process where rocks, particularly feldspar-rich igneous and metamorphic rocks, are altered into clay minerals. This transformation is primarily driven by the chemical weathering of existing minerals in the presence of water. The key minerals involved are typically feldspars, which are abundant in many common rocks. Water, especially when it contains dissolved acids, acts as a solvent and reactant. Over geological timescales, these reactive fluids penetrate the rock and slowly break down the feldspar structure.

The process involves the hydrolysis of feldspar, where water molecules react with the mineral lattice, leading to the formation of new clay minerals such as kaolinite, illite, or smectite, along with dissolved ions like silica and alkali metals. This alteration can occur in various environments, including near the Earth's surface where weathering is active, or at greater depths under hydrothermal conditions. Argillization is a significant process in soil formation, as clays are a fundamental component of most soils, influencing their texture, water retention, and fertility. It also plays a role in the formation of sedimentary rocks, where the resulting clay minerals can be transported and deposited. The degree and type of argillization depend on factors like the original rock composition, the duration and intensity of water-rock interaction, temperature, and the chemical composition of the pore fluids.