The red–orange patina developed on a monumental dolostone

Orange and reddish patinas developed on a dolostone of the cathedral of Lleida (Spain) have been analysed and characterised by XRD, SEM/EDX, ICP/MS, optical microscopy and Mِssbauer spectroscopy. From the experimental data, a biologically induced transformation of the dolomite rock forming crystals, which form a dolomitic patina of micrite size, can be stabilised. Furthermore, the iron oxides as determined by Mِssbauer spectroscopy play a role as colouring patina, together with organic matter from the bioactivity. Erosive and constructive processes, as determined through the SEM observations, lead to aesthetical and microstructural changes in the stone surface.