Pyrite Decay of Large Fossils: The Case Study of the Hall of Palms in Padova, Italy

Pyrite decay is arguably the major problem in geological and palaeontological conservation, as it can cause total destruction in valuable specimens. Various methods have been devised since the 19th century to treat and prevent it with different degrees of success. Nevertheless, the conservation of large fossils at risk of pyrite decay remains an unsolved issue, because a feasible method for maintaining them in a controlled microclimate that is suitable for specimens on public display has remained elusive. This paper describes the study carried out to investigate the alterations that developed in a large fossil palm of the collection of the Museum of Geology and Palaeontology in Padova (Italy), already treated for pyrite decay several years before. Results of X-ray powder diffraction and Raman spectroscopy performed on samples collected from that fossil palm confirmed that the alterations were due to pyrite decay. The microclimate indoors (inside showcases and in the Hall itself) and outdoors was monitored for one year to investigate its possible relation with the damage observed. The measured thermo-hygrometric conditions exceeded the recommended thresholdsforthepreventionofpyriteoxidationandindicatedthefossilswereathighriskofdamage from that process. This study demonstrates that treatment alone is not sufficient for the conservation of fossils at risk of pyrite decay and that it can be ineffective without a proper management of the microclimatic conditions under which the fossils are preserved.