Genesis of Secondary Al‐(Fe‐)ChloritesComparing the results of soil investigations with those obtained from laboratory syntheses it was concluded that secondary Al‐Fe‐chlorites in soils of moderate cool‐warm‐humid climates mainly develop through protonisation of Al and Fe in the mineral structure of expanded dioctahedral vermiculites with subsequent hydrolysis in the interlayer space. In this process characteristics of the mineral itself (e.g. layer charge) as well as carbonic acid and soil organic acids (as proton suppliers) are the most important factors.From this, the further conclusion was drawn that in the pH‐range 6, 5–6 secondary chlorites begin to develop increasingly until pH5 (development conditions) and in the pH‐range 5–4,5“conservation conditions” exist. ‐ At pH<4,5 secondary chlorites are unstable (dissolution conditions) through protonisation of Al‐Fe‐hydroxy polymers (reverse of hydrolysis) with subsequent solubilization and leaching especially through complexation by soil organic acids. ‐ As remaining minerals in this weathering sequence smectites occur, resulting from the decrease of layer charge in vermiculites through the chloritization process, thus indicating that chloritization may be an important process for the genesis of smectites u