ABSTRACT
This chapter shows how the concept of fractal dimension may help to quantify the relationship between microtexture and accessibility to an inert gas. This will be illustrated mainly on the most active mineral components of soils: smectite clays. On a more qualitative level, the relationship between accessibility and reaction rate is also addressed. Very little in the case of more or less rigid fibrous clays and in the case of rigid kaolinite or illite platelets, except perhaps the assumption that the lateral surface area is negligible compared to the basal surface area. There is ample experimental evidence that some of the most active components of soils, smectite clays, may generate fractal structures at length scales between a few nanometers and a few millimeters. The scaling exponents characterizing the geometry of this fractal space are strongly related to the interactions between the elementary clay sheets at the molecular scale, as controlled by adsorbed ions or organic compounds.
