Natural Stones Used in the Orsi-Marconi Palace Façade (Bologna): A Petro-Mineralogical Characterization

Ancient buildings are important components of the Italian Cultural Heritage and, since the Etruscan Period, Bologna (north-eastern Italy) has always been one of the most flourishing cities both culturally and economically in the Italian and European panorama. The Orsi-Marconi Palace in Bologna presents a monumental façade decorated with many sandstone ornaments of the 16th century. Different samples from different parts of the façade of the building were collected and firstly characterised by macroscopic observations to determine the structural aspect. A petro-mineralogical study on the surfaces of the samples was conducted using a stereomicroscope and Optical Transmitted Light Polarized Microscopy. In addition, X-Ray Fluorescence and X-Ray Powder Diffractometer analyses were carried out to better understand the mineralogical composition of the sandstone materials used and the degradation products from the façades of this historical building. The aim of this work was to better understand how to revalue the sandstone decorations severely affected by deterioration phenomena.