Abstract: This contribution reviews the work done at Ghent University, together with some unpublished recent work. Next to the survey of clay minerals from soil samples for the soil mapping organization, the group has been concerned with the polytypism of micas, the alteration and transformation of clay minerals, and the role of migration of iron in mica-type structures under influence of temperature or chemical treatment. A study of growth spirals of biotite crystals threw some light on the origin and possibility of the existence of ordered sequences with great repeat distances, and also on the complexity of crystals of this type. The presence of dislocations in mica is also shown by examination of “bending figures” produced by indentation. A study of clay minerals in soil fractions from a limited area, reclaimed fronl the sea between the eleventh and nineteenth centuries, indicated great variation in mineral composition. If one accepts the logical working hypothesis that the mineral composition was homogeneously distributed at the start, one must accept a rapid transformation at particular spots. This evolution seems to proceed from muscovite (illite) toward montmorillonite. Neoformation of a small quantity of kaolinite accompanies the transformation to montmorillonite.
Experiments carried out to achieve this process in the laboratory showed that micas submitted to a stream of CO2 dissolve rather rapidly in presence of water. All attempts to obtain clay minerals from the obtained solutions failed, except one, when small quantities of montmorillonite and kaolinite were formed. The thermal evolution of glauconite and the location of iron ions were also studied. Some remarks on formulas of clay minerals are presented.