The mass balance approach (Table 2) shows that the enrichment in light 28Si of secondary minerals of Bhs horizon (−2.31‰) compared to the “unweathered” secondary minerals in the BC horizon (−1.40‰) partly explains the depletion in light 28Si of secondary minerals in the clay fraction of E horizon (+0.64‰) for the oldest soil (Podzol CB- 335 years).