Scientists from the Chinese Academy of Sciences investigated the mechanisms driving change in the characteristics of clay under ambient temperature and pressure. Specifically, they studied the colour changes of Zhanjiang clay, which changes from greyish green to yellowish brown when exposed to the atmosphere. They found that the changes were driven by a reaction of oxides of iron in the clay. The oxidation of the iron oxides reduced the plasticity, sensitivity and structural yield stress of soil.
This transformation of soil properties by the atmosphere was not due to inherent changes of minerals, but motion effects and chemical reactions of the water–soil–electrolyte–atmosphere system which caused the remodelling of micro-structures in soil particles, the study found.