Investigation of lichens using molecular techniques and associated mineral accumulations on a basaltic flow in a Mediterranean environment

The role of lichens in the breakdown of rocks in various environments is well documented. We investigated the formation of secondary minerals under 13 different fungal species growing on a basaltic flow in Sanliurfa (Turkey) to understand the influence of lichen species on the transformation of minerals in a Mediterranean environment. We used molecular technique (rDNA sequence) to identify 13 different species of lichens (7 crustose, 5 foliose and 1 pathogenic). X-ray diffraction and scanning electron microscopy were used to determine the composition of mineral accumulations. The formation of quartz and 2:1 phyllosilicates in various layers (top, brown and white) of the weathered basaltic flows under all the lichen colonies may be the result of precipitated silica alone (quartz) or in combination with aluminum (2:1 clays) released as a by-product during the breakdown/weathering of primary silicate minerals present in the basalt. However, aeolian deposition may also be a possible source of these mineral species. Whewellite, a calcium oxalate mineral, accumulates in the weathered basalt underneath all the species of lichens. We believe that the formation of whewellite was due to organic acids excreted by fungal hyphae to dissolve primary minerals (e.g., olivine and feldspars); this lichen-mediated process released enough calcium and generated oxalate necessary for the formation of whewellite.