Saxicolous lichens and associated mosses, and their weathered and fresh rock zones, were collected from a number of locations. All material was treated with hydrogen peroxide and infrared spectra of the remanining mineral matter were obtained.Spectra of the mineral matter obtained from the lichens and mosses differ generally from those of the substrata. There is evidence that quartz and dioctahedral structures could be products of weathering of rocks by lichens and mosses. It is likely that saxicolous lichens obtain at least part of their minerals from the substrata. There is no indication of the presence of magnesium or of carbonates in the peroxidized material of lichens obtained from calcareous or dolomitic substrata. Peroxidation of the organic tissues leads, in the presence of calcium, to the formation of calcium oxalate; the relative intensities of the bands related to calcium oxalate, in particular those at 1325 and 780 cm−1, may be used to assess the amount of calcium present. It is suggested that this change in intensity may be a useful criterion in evaluating the transformation of Chernozemic humic acids to Podzolic humic acids in soil.