ABSTRACT
The result of chemical solution appears paradoxical. To show this, let us start with a collection of particles containing sands, silts and clays at the same time, the point representing which is located at the centre of the textural triangle (Fig. 3.18, left half, point X). Intuitively, since each particle reduces in diameter, we could expect evolution towards clay particles. But in reality, the smallest particles have a greater surface area/mass ratio. They are therefore more susceptible to dissolution and disappear in greater proportion by weight. The result is a trajectory towards the sand corner, of course at the cost of a very pronounced loss
in total mass. In detail, dissolution at first affects mainly the particles of clay size, especially the fine clays, leading to an evolution towards the base of the triangle along a straight line passing through the clay corner (see argilluviation above). Then the silts are attacked in their turn, whereby an inflection is seen in the trajectory towards the sand corner. It is actually observed in nature that ancient soils have an evolution of the skeleton grains similar to what is simulated (Fig. 3.18, right). If we start from a collection of already sandy particles (point Y), there is no trajectory observable by simulation. The point representing the collection remains almost in place in the triangle. In other words, it is impossible to create a clayey or even silty material starting from a sand composed of particles of size 2000 µm. When the diameter will be reduced to 1000 µm, this sand will continue to be counted in the coarse sands (particle-size class 2000 µm-200 µm). Its size class will not have changed in our system of measurement. However it would have lost 87.5 per cent of its mass! The chemical reduction of sands does not change the particle-size class! The sea beats its waves on the sandy shores whose particles are subjected to intense dissolution, which does not, however, prevent them from remaining sandy. On firm land we may find very mature soils (e.g. Podzols) subject to processes of intense solubilization, but which have a stable sandy texture from one horizon to another.
