Biodeterioration of granite monuments by Ochrolechia parella (L.) mass: an FT Raman spectroscopic study.

Ochrolechia parella is one of the most abundant lichens colonizing granite monuments in the region of Galicia (N.W. Spain). Its interaction with granite used in the construction of four ancient monuments was studied using FT Raman spectroscopy to evaluate the production of calcium oxalate by this lichen and the relationship of this production with different environmental conditions, particularly humidity. The results obtained showed that Ochrolechia parella is an aggressive colonizer, causing chemical disturbances to the granite through the formation of both calcium oxalate monohydrate and dihydrate. Apothecial development appears to be related to the production of calcium oxalate, and humidity determines the state of hydration of the calcium oxalate in the thallus.