The stones in monumental masonry buildings of the “Val di Noto” area: New data on the relationships between petrographic characters and physical–mechanical properties

The Palazzolo Formation calcarenite, commonly known as “Pietra di Noto”, has been widely used in the late Baroque monuments of the Val di Noto area. In this work, two different lithofacies have been identified through a minero-petrographic and physical–mechanical characterisation of the Noto stone samples. These latter have been taken out from three quarries, two of which are located near to Noto Antica (Porcari and Leone), and one next to Palazzolo Acreide (Camelio). Samples from Camelio have a white-cream colour and a higher sparry cement abundance than those from the Porcari and Leone quarries, which display a yellowish colour, a minor resistance and a more heterogeneous texture due to the presence of bioturbation (trace of fossils). The greater compactness of samples from Camelio compared to the other two is related to their higher ultrasonic velocities, better mechanical properties and reduced capability to absorb water by capillarity and total immersion which are related to the textural features. The existence of two lithofacies better explains the heterogeneity of degradation forms (chiefly consisting of differential degradation, alveolization, detachment and chromatic alteration) that can be observed on the monuments built in these stone materials. The main causes of deterioration have been related to bioturbation, as well as to the occurrence of expandable clay minerals (smectite) and to salt crystallization. The presence of bioturbation also affects the mechanical characteristics of these stones.