ABSTRACT
The nature of new mineral formation in the near-surface zone of the lithosphere is determined by the ambient conditions of temperature and pressure and the flux of materials provided by the processes of weathering and leaching. The low temperature and pressure that prevail in this zone mean that any mineral formed will have a very fine grain size and a disordered structure. From a general knowledge of silicate structures, it is apparent that there are two possible routes for physil formation: first, from micas by simple transformation, in which the original sheet structure remains more or less unaltered and, secondly, from mafic minerals and feldspars, which need to be broken down to a much greater extent, before a phyllosilicate structure can be assembled from the fragments. The hydrothermal inheritance also explained the presence of the abundant calcium carbonate, which could not be explained in terms of epimorphism.
