Abstract: The following recent work is reviewed.
In the Triassic basin of the Jura detrital illite changes into chlorite (chlorite and chloritic mixed layers) toward the middle of the basin.
In the profiles of podzolic soils and podzols, illite and chlorite change, through illite-vermiculite and chlorite-vermiculite stages, into vermiculite.
In Cambrian sandstones of the Sahara two successive diagenetic changes have taken place: early postdepositional kaolinization, and illitization by salt waters.
Neoformation of aluminomagnesian clays in the alkaline sediments of the Eocene basins in Africa produces a sedimentary and geochemical sequence of montmorillonite, attapulgite and sepiolite.
When siliceous neoformation is produced by crystal growth, the growth is regular in the production of quartz, and irregular or hindered in the formation of chalcedony or opal-cristobalite.
Kaolinite has been synthesized at low temperatures in dilute solutions.
Transformations of triphormic clay minerals in the hydrosphere consist of a progressive expansion of layers. Environment controls the equilibrium between interlayer cations and adjacent layers. Siliceous and argillaceous neoformation consists of organization of silica tetrahedrons; this organization depends on the environment and especially on the environmental cations. Transformation by diagenesis is more intense and allows direct passage from illite to kaolinite.