The gold-decoration technique of electron microscopy is used to study the surface microtopography of natural (001) surfaces of sudoite collected from a hydrothermal vein of the Berezovsk gold deposit, Central Urals, Russia. Only closed step patterns with malformed and/or nearly circular islands were observed on the (001) growth surface of sudoite crystals, implying a twodimensional nucleation mechanism. This is in contrast to the spiral step patterns commonly recognized on growth surfaces of other clay minerals, such as illite and kaolinite, formed under hydrothermal conditions. It is inferred that the crystallization of sudoite occurred under relatively higher temperatures and/or from more highly supersaturated fluids than many other hydrothermal clay minerals so far described.

Mineralogical and geochemical studies of Cretaceous segments of Argille Varicolori and Flysch Rosso successions from the southern Apennines allow their provenance and history to be evaluated.

The occurrence of detrital kaolinite and fine-grained Fe-oxyhydroxides, the strong depletion of Na2O, K2O and CaO, and the enrichment in the transition elements document severe alteration in the source areas. Nevertheless, mineralogical and geochemical features able to discriminate the shale families are still preserved. The presence/absence of rock fragments derived from a ‘crystalline’ source, the significant chemical differences as well as the characteristics of clay minerals, discriminate the studied shales. The absence of indications suggestive of mixing of the detrital components favour the hypothesis that the two shales were deposited in distinct basins which probably received contributions from continent-ocean convergent areas (Argille Varicolori) and from more stable areas (Flysch Rosso).