The biodeterioration of diverse natural and man-made substrata by Caloplaca aurantia, Lecanora muralis and Acarospora oxytoma has been studied using FT-Raman spectroscopy with 1064 nm laser excitation. Each of the three lichen species produce relatively large amounts of calcium oxalate in encrustations at the thallus-substratum interface during the biodeterioration process; the Raman spectroscopic technique is capable of identifying non-destructively the monohydrate, with ν(CO) stretching bands at 1463 and 1496 cm - 1 and the dihydrate, with a ν(CO) stretching band at about 1475 cm(su-1). In this work, the presence of calcium oxalate monohydrate and dihydrate in the lichen encrustations is identified for these high-oxalate producing biodeteriorative lichen systems. The results indicate that the lichens adopt different methods for the production and removal of the hydrated calcium oxalates in the encrustations.