Abstract: In the first part of this paper the formation processes of pure octahedral hydroxides are investigated. Conditions of synthesis of aluminum, magnesium, iron and mixed Al-Mg, Al-Ca, Al-Fe systems axe successively reviewed. In every case crystal growth in deionized medium allows one to figure out genetic conditions.
The second part deals with the conditions required for the development of the octahedral layer in the presence of silica, i.e. the clay mineral synthesis. Experimental conditions remain always as nearly as possible to those observed naturally.
Trioctahedral minerals are rather easily obtained at ordinary temperature and pressure. The evolution of the magnesium-silica system is described. Synthesis of dioctahedral layer lattices, such as those of the kaolin minerals, appears more difficult to perform under the same conditions. Initial organization of the starting materials plays an important role in this case and procedures are described.
Finally, interactions of octahedral and silica layers are studied. The study of infrared spectra in the 9–11µ region permits such observations. Characteristic changes in the spectral region of Si-O stretching allows one either to follow the octahedral destruction (by acid attack or dehydroxylation) or the octahedral layer formation in kaolinite synthesis.