The clay concentrations of economic value are composed of a succession of clays, sands and pebbles. This torrential-stream deposit, close to enlaced rivers, laid to the deposition of sandy-clayey materials, with a variable iron content, coming from a lateritic weathering, of the French “Massif Central” granites. The presence of numerous lignite rich levels indicates that the deposit was performed in the presence of abundant organic matter, leading to important pedogenetic and diagenetic possibilities of evolutions. These chemical and mineralogical evolutions (dissolution–crystallization) allow the neo-formation of kaolin and gibbsite, as well as iron sulfide.