Argillic alteration is hydrothermal alteration of wall rock which introduces clay minerals including kaolinite, smectite and illite.
The process generally occurs at low temperatures and may occur in atmospheric conditions. Argillic alteration is representative of supergene environments where low temperature groundwater becomes acidic.
Advanced argillic alteration occurs under lower pH and higher temperature conditions.
Phyllic alteration is often closely associated with argillic alteration, which occurs at lower temperatures and dominantly affects plagioclase.