Argillic alteration is hydrothermal alteration of wall rock which introduces clay minerals along with kaolinite, smectite and illite. The technique normally happens at low temperatures and can arise in atmospheric conditions. Argillic alteration is consultant of supergene environments wherein low temperature groundwater will become acidic.

Argillic assemblages encompass kaolinite changing plagioclase and montmorillonite changing amphibole and plagioclase. Orthoclase is normally strong and unaffected. Argillic grades into phyllic alteration at better temperatures in an ore deposit hydrothermal system.

Advanced argillic alteration happens below decrease pH and better temperature conditions. Kaolinite and dickite arise at decrease temperatures while pyrophyllite and andalusite arise below excessive temperature conditions (T > 300°C). Quartz deposition is common. Alunite, topaz, zunyite, tourmaline, enargite and tennantite may arise. Greisen alteration is similar.