The presence of crusts of different composition and origin is a threat to cultural heritage throughout the world. In Brazil, most of the prehistoric paintings are found on rock walls exposed to atmospheric weathering. For this research, samples were taken in the Cavernas do Peruaçu National Park, located in Minas Gerais, Southeastern Brazil. The physico-chemical characterization was carried out using Thermogravimetry (TG), Differential Thermal Analysis (DTA), Energy Dispersive Spectroscopy (EDS), X-ray Powder Diffraction (XDR) and Fourier Transform Infrared Spectroscopy (FTIR). The analyses indicated the presence of aragonitea CO3, calcium carbonate), distinguished by XRD, as a degradation product and showed weddellite (CaC2O4· 2H2O, calcium oxalate dihydrate) and gypsum (CaSO4· 2H2O, calcium sulfate dihydrate) in areas where a lichen grows. This microorganism, probably the lichen Aspicilia calcarea, has already been found in archaeological sites around the globe.