Lichen weathering of minerals: implications for pedogenesis

Summary The weathering of primary rock-forming minerals beneath crustose lichens is due principally to the activity of the fungal component in excreting extracellular organic acids, particularly oxalic acid. This results in extensive surface etching of the minerals, the conversion of some minerals to siliceous relics, the formation of poorly ordered weathering products and the crystallization of oxalates at the rock/lichen interface and within the lichen thallus. Interpretation of these features is facilitated by the fact that they can be simulated experimentally. The relevance of lichen weathering to the pedogenic weathering predominant in soils under a cool temperature climate is discussed.