Study of the biogenic weathering of calcareous litharenite stones caused by lichen and endolithic microorganisms

The aim of this work was to study the bioweathering processes caused by lichen and their accompanying endolithic microorganisms living in calcareous rock of the Roman Cathedral of Jaca, Spain. Samples were taken from Cathedral. Diploicia canescens (Dicks.) Marsal., Lecania rabenhorstii (Hepp) Arnold., Caloplaca and Xanthoria lichen species were detected on the stone surface. After preparation the samples were examined with scanning electron microscopy equipped with a back-scattered electron detector and energy dispersive x-ray spectroscopy. The results demonstrated various types of stone damage caused by lithobiontic microorganisms: Chlorite sheet separation by algae, calcium carbonate nodule trapping by hyphae, and cross-linear alteration and subsequent pellicular alteration patterns in calcite grains by hyphae-were the main bioweathering features of the calcareous substrata. Both epilithic and endolithic fungal cells were found to be responsible for stone decay. (C) 1998 Elsevier Science Ltd. All rights reserved.