Argillic alteration is hydrothermal alteration[citation needed] of wall rock which introduces clay minerals including kaolinite, smectite and illite.
Argillic alteration is representative of supergene environments where low temperature groundwater becomes acidic.
Argillic grades into phyllic alteration at higher temperatures in an ore deposit hydrothermal system.
[1] Advanced argillic alteration occurs under lower pH and higher temperature conditions.
Alunite, topaz, zunyite, tourmaline, enargite and tennantite may also occur.