Abstract
Summary: The system SiO2 ‐AlOOH‐Fe2 O3 ‐H2 O is used to show certain short‐comings in the use of single minerals to index weathering stages. An alternative (analogous to the metamorphic facies concept) is proposed in which three stages are recognized, one of which can already be defined in terms of mineral assemblages, while the two earlier stages should eventually prove open to this treatment.