An experimental pedology research project, based on a “process-system” pedogenetic model, was initiated to investigate the weathering of Phlegraean Yellow Tuff (PYT) – the yellow facies of the Campanian Ignimbrite with phillipsite > chabazite – as representative of the parent rock material as the soil-forming factor. PYT was weathered by water (W) and tannic acid solutions (TA) at concentrations ranging from 3 × 101 to 3 × 104 μmol l−1. The most concentrated TA solution (3 × 104 μmol l−1) showed the greatest extracting efficiency. Na and K were continually solubilized by W; Al, Ca and Mg contributed to the ionic composition of all the TA supernatants. A significant dissolution of the amorphous component and an associated decrease of the zeolite content, especially phillipsite, were noted. The features of PYT weathered outcomes fitted the “process-system” model very well. PYT showed a pedogenic potential, in being prone to weathering, as well as in releasing elements of importance for plant settlement and development, such as K, Ca, Mg and Fe.