Illitic-smectitic clays were matured with a ferruginous, bicarbonate-rich and sulphate-rich water for different periods of time (7, 15, 30, 60 and 90 days), and subjected to discontinuous stirring, to test their use in pelotherapy. A progressive degradation of the clay minerals was observed during the maturation process, with a reduction in the illite and smectite crystallinity, in the percentage of smectites and in the phyllosilicate content. The percentage of <2 μm particles also decreased. These modifications caused changes in the clays’ physicochemical properties, which are evident in an increase in their plasticity index and in slower cooling of the peloid, both of which improved the clays’ effect in pelotherapy.
