Transformation of iron-bearing kaolinite to iron-free kaolinite, goethite, and hematite.

Ferruginous clay partings occur in Upper Triassic limestones in Israel. These contain Fe-rich anhedral kaolinite and euhedral Fe-free kaolinite as hexagonal flakes covered with acicular goethite and platy hematite, as well as cubes of goethite with minor kaolinite. The anhedral kaolinite appears to be detrital, the hexagonal plates authigenic, and the cubes pseudomorphs after pyrite. A slow alteration process was involved in the kaolinite change, probably induced by pH and Al/Fe ratio changes caused by oxidation of reduced components in a semi-closed sediment-mud system. This process may have ultimately produced the overlying kaolinitic flint clays. -D.F.B.