Microorganisms (bacteria, fungi and others) are considered to be the pioneers of the settlement under extreme conditions and take an active part in biomineralization and soil formation. We studied biofilms and for the first time identified the presence of microbial biomineralization in extreme conditions of Tolbachik Volcano area, Russia. Rock samples with lichen / cyanobacteria biofilms were studied by a complex of methods (optical and scanning electron microscopy, powder X-ray diffraction and energy-dispersive X-ray spectroscopy). We found that the acidic environment of biofilms favor oxalate biomineralization under the action of lichens and suppresses the carbonate biomineralization under the action of cyanobacteria. Calcium (whewellite, Ca(C2O4)·H2O, and weddellite, Ca(C2O4)·(2.5-x)H2O (0 ≤ x ≤ 0.25)) and copper oxalates (moolooite, Cu(C2O4)·nH2O) were found in lichen biofilms. Direct relationship between the age of lichen and intense of biomineralization was discovered. It was shown that the lichens not only extract calcium and heavy metals (Cu, Pb) from the basaltic rock (both in situ and from weathered particles of the same rock brought by the wind) but increase their content in biofilm. The lichen species Psilolechia leprosa, Sarcogyne hypophaea, Rinodina cf. gennarii, and Ochrolechia subplicans subsp. subplicans can form oxalates. It was also found that (1) calcium and copper oxalates can be localized in the same lichen, (2) the species producing oxalic acid do not always produce oxalates and (3) the ratio of whewellite and weddellite formed by the same species lichen can vary significantly. Obtained results show high abundancy of biomineralization in terrestrial environment, including extreme and provide some insights into mechanisms of microbial biomineralization.