Biomineralization Processes on Rock and Monument Surfaces Observed in Field and in Laboratory Conditions

Abstract

Monument surfaces lack mechanisms of self-protection and regeneration but tend to accumulate inorganic and organic substances from the surrounding environment, most of which can serve as nutrients for many microorganisms. When the precipitation of mineral phases is faster than the decay mechanisms, as a consequence of interactions among rock surfaces, pollutants, climate, and microorganisms, then crusts and patinas are formed. We report laboratory studies to characterize microorganisms, recreate geomicrobial processes, and characterize the mechanisms involved through the use of experimentally infected stone slabs. The aim of our article was to combine the characterization of natural stone and microflora presently colonizing rock surfaces and the laboratory experiments in which controlled conditions were applied to the observation of geomicrobial processes leading to surface deterioration. The results show that the majority of bacteria isolated from stone surfaces are able to precipitate CaCO3 in the form of calcite. This phenomenon was strictly controlled by the growth of microbial colonies on a solid substrate. In infected slab stones the process was reproduced, but newly mineralized phases contained phosphate (apatite and wilkeite).