AN APPROACH TO STONE AND FRESCO LICHEN BIODETERIORATION THROUGH FOURIER-TRANSFORM RAMAN MICROSCOPIC INVESTIGATION OF THALLUS SUBSTRATUM ENCRUSTATIONS

The Fourier transform Raman spectra of thallus-substratum interfaces o f Xanthoria parietina growing in situ on sandstone and gypsum were obt ained for the first time. The presence of small amounts of calcium oxa late in thallus-substratum interfaces was confirmed spectroscopically and evidence for biodeterioration via lichen metabolic by-products was also noted. Although the oxalate determined spectroscopically was in good agreement with the results from thermogravimetric measurements th ere was also spectroscopic evidence for incorporation of stone particl es into the lichen encrustation. Comparisons are made with Raman spect roscopic studies of the thalli of the high oxalate-producing lichen Di rina massiliensis forma sorediata. The Raman spectra Ochrolechia parel la growing in association with Xanthoria parietina on maritime sandsto ne were also recorded and the spatial discrimination of the techniques for these high and low oxalate-producing lichens was demonstrated.