Clay Minerals in Weathered Rock Materials and in Soils

Since Georges Millot’s initial contribution to clays and his thesis on the relationship between composition and development of sedimentary clayey rocks defended in 1949, half a century has passed by. So much has been discovered on clays during that period that it would almost be impossible either to list the work undertaken or to give a comprehensive account of the present situation in a concise presentation. I have, therefore, selected some topics in which Georges Millot was mainly interested and I will proceed according to his methods, i.e. I will present facts observed in nature, examine them with the best-suited techniques available and finally organize the data into a coherent picture, even though I am not as bright as he was. I will try and aim for clarity rather than for the enlightenment which was his.