The Montagnola Senese marbles (Siena, Italy). Study of the microfabric and physical decay processes.

The aim of this study was to characterize the Montagnola Senese marbles (Siena, Italy), widely used in historical Sienese monuments, and to define the relationships between the marble’s microfabric and physical decay processes. A mineralogical-petrographic analysis of the most common varieties was conducted by light microscopy, computerized image analysis, cathodoluminescence, XRD and X-ray textural goniometry. Heating and cooling cycles were applied to different lithotypes to evaluate the role of the microfabric in physical decay induced by thermal stress. Water absorption trials were conducted on unaltered and aged samples to test the physical features and to evaluate the effects of artificial ageing. Finally, we studied the decay behaviour of these marbles in monuments in the historical centre of Siena. The results indicate markedly different water absorption properties of the various marble varieties and differences in their decay behaviour, both in the laboratory and in the monuments. This is mainly related to the microstructural features of the marbles, especially the grain size and grain boundary corrugation.