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The examination of the surface deposit of various lichens with X-ray diffraction methods, correlated with scanning electron microscopical (SEM) studies, have shown that calcium oxalate is present as two different hydrates; weddellite (CaC2O4-(2 + x)H2O), in three slightly different morphologies, and whewellite (CaC2O4H2O). The reason for the formation of calcium oxalate is not known and the presence of the various crystal forms is yet to be explained. However, the various hydrates may have some role in the water balance as they are different in dry and humid sites.

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