Microstructural study of the origin of color in Rosa Porrio granite and laser cleaning effects

In this work we have studied the micro- and nanostructure, together with the chemical composition, of the feldspar areas of Rosa Porrio granite in order to relate them with the fading of pink color produced after laser cleaning. Transmission electron microscopy and related techniques, such as electron energy-loss spectroscopy, energy-dispersive spectroscopy or high-angle annular dark field imaging, have been mainly employed in this work, due to their high spatial and point resolution. The presence of a high quantity of ZnFe2O4 nanoparticles embedded in vitreous KAlSi3O8 in the original granite feldspar areas has been detected. We have observed a very low number of these nanoparticles in the irradiated granite, together with a severe surface damage (through scanning electron microscopy images), which can be directly related to the loss of the characteristic pink hue of this material.