Dickite occurs over wide areas along the Italian Apennines strip throughout Italy, mainly in the allochtonous ‘varicoloured’ clay-shale formation. Morphological, fabric and crystallochemical features suggest an authigenic origin, from pore solutions. The nature of the solutions and the process of dickite formation, including hydrothermalism, diagenesis or supergene evolution have all been discussed. Stable isotope analysis (O, H) was performed to investigate these points. The δD values of dickite range between −63.7 and −79.1‰ (SMOW) and δ18O between +21‰ and +16.1‰ (SMOW), and are similar to those reported for kaolinites formed in equilibrium with meteoric waters. The data fall along the ‘Line of Meteoric Kaolinites’, supporting an origin involving meteoric waters and low temperatures. The isotopic compositions of the waters are within the range of Apennines meteoric water, and the temperatures derived are close to surface conditions. Contributions of diagenetic, hydrothermal or metamorphic waters must be discounted. The authigenic dickite from ‘varicoloured’ clays of the Italian Apennines formed by precipitation from flushing meteoric waters whose ingress was favoured by repeated surface erosion.

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