Accessory green ferric clay occurs in fluvial litharenites of the Early Triassic Rewan Group. Although resembling glauconitic minerals in thin-section, electron microprobe analyses indicate that the green ferric clay is mainly ferric illite. The ferric illite may have formed in a small hypersaline lake or well drained, flood-plain soil, and its presence in the Rewan Group cannot be used to support a notion that the unit is partly marine influenced. Identification of the ferric illite by electron microprobe analysis shows that some green ferric clays, particularly those that resemble glauconitic minerals optically, may require precise quantitative elemental analysis before they can be used as a basis for environmental interpretation. Green ferric clay in the Rewan Group also includes detrital celadonite that most likely originated in a volcanic arc setting.