Many Vertisols of the world tend to alter into Luvisols and various processes have been invoked to explain this transformation. We have studied a Luvisol (Hypereutric Chromic)/ Vertisol (Humic) catena in the Indian Karnataka Plateau that has developed on complex metamorphic rock under semi-arid conditions. Although the catena differentiation is majorly driven by lithology, vertic properties of the Vertisol decrease towards the soil surface. To understand this, we investigated horizons chemistry (total elements, dithionite Fe and pH) and mineralogy with a closer insight into fine clay (< 0.1 μm) mineralogy using FTIR and XRD coupled with diagram decomposition with DECOMPXR to evidence interstratified clays. We were able to establish that the weathering process in the Vertisol can be divided in two steps. 1) In the saprolite fast weathering of chlorites and amphiboles produces ferriferous beidellite by dissolution and neoformation. This process continues in vertic horizons until primary minerals disappear. 2) Smectite transformation into kaolinite via an interstratified K/S also begins in the saprolite and takes over smectite formation in vertic horizons. In the upper part of vertic horizons, pH drops together with the total reserve in bases because basic primary minerals are exhausted and are no longer available to buffer the chemical environment through their hydrolysis. Therefore conditions become less prone to smectite stability and exalt its weathering which hinders the vertic typical shrink-swelling. Bases depletion implies their leaching away from the horizon, laterally or vertically. This leaching could account for a part of clay depletion along with the mass loss due to smectite transformation. Meanwhile weathering leads to relative accumulation of quartz sands. The resulting coarser texture is also unfavourable to vertic properties. As a conclusion, factors implied in Vertisol alteration here, are the combination of weathering processes with the drainage of elements and possibly of clay particles.