Chromatic weathering of black limestone quarried in Varenna (Lake Como, Italy).

The causes of chromatic weathering in black limestone have been investigated on samples from the main quarry of Varenna (Lake Como, Italy), which provided building stones for Lombard architecture. Our studies have been carried out combing colorimetric, mineralogical, chemical, microstructural and geochemical observations. The results suggest that the chromatic weathering affecting the surfaces of black limestone is not due to oxidation of the original organic matter present in the bulk, as believed. Chemical and mechanical weathering associated with the deposition of new organic matter are the most important phenomena occurring on the surface, leading to a diffuse roughness of surface and de-cohesion.