Causal relationships between the genesis of a mineral deposit and the processing technology were investigated for European bentonites from the economically most important regions, Milos, Bavaria and Sardinia. 1. The amount of sodium carbonate can be clearly determined by the definition of a chemical and technical degree of activation, a new mechanical solution, described in this paper, and a newly developed method for the liquid flow limit. 2. The dependence of product properties on the genesis of the deposit and the activation technology have been shown. The proposed processing technology opens up possibilities to achieve significant savings thanks to better product properties. 3. The ESEM investigations on the morphology yielded information which contributes to the explanation of the reasons for the product properties. 4. The phenomenon of the cement-stability of a bentonite with a low smectite content from Milos has been discovered. With the sodium ions which are present from the activation, the high proportion of soluble silica leads to a reaction which is not based on the original rheological properties of bentonite.