8. Weathering mechanisms

In an atmospheric environment, constantly changing weathering conditions give rise to a specific phenomenology. A layer of alkali-depleted hydrated glass is formed by selective dissolution. However, unlike the facies observed during weathering in aqueous media, the weathering layers formed in a real atmospheric environment are chemically heterogeneous and extremely fragile, as they are severed by numerous cracks that lead to the formation of scales and result in significant material loss. At the same time, neocrystallizations form either on the surface or inside the cracks.

All these alteration facies reflect a number of mechanisms, which are very similar to those described in aqueous media, but with different respective weights (figure 12 )....