Spectroscopic investigation of iron stains on carbonatic stones

In Cultural Heritage carbonatic stones, such us Carrara and Travertine, sometimes may shows anaesthetically chromatic alteration, due to the presence of metal oxide, such as Iron oxides, diffused on the surface. In fact Iron stains, that may be composed by different iron oxides (lepidocrocite, goethite or hematite), can be considered a common form of alteration (UNI 11182-2006). The elimination of these stains is strongly related to the mineral phase formed and then to their solubility. For this reason it is important to know what we are going to remove. In this study we report results obtained by a natural staining of Carrara marble specimens, i.e., exposed in outdoors environment, in contact with Iron (in form of cubes, nails) for one or more season. The speciation state of the so formed iron stains was investigated by means of spectroscopic techniques such as Raman, Mössbauer and X-ray Photoelectron Spectroscopy.