Biomineral deposits and coatings on stone monuments as biodeterioration fingerprints

Study of the Geochemical Decay and Environmental Causes of Granite Stone Surfaces in the Built Heritage of Barbanza Peninsula (Galicia, NW Spain)

“…Thus, despite the weathering indices probably not being resolutive enough, the SEM provided evidence of weathering. Due to the presence of biological colonization and the high humidity and average annual precipitation, we cannot discard the biological weathering as responsible for these effects [14]. Indeed, Ti and Fe were identified under the SEM, previously reported in FRX, possibly related to oxides (Figure 9l).…”

“…There is a significant positive correlation between oxides of Fe2O3 and MgO (Figure 4d), fundamentally due to the content in biotite and with ZnO related mainly to Fe-Zn oxides (Figure 4e). These elements are interesting as the oxidation of Fe and Mn due to chemical and biological processes usually results in visible chemical weathering effects such as stains and coatings [14,25] Other elements, such as P2O5, are present in all samples with an average of 0.4% and showing a positive correlation with CaO (Figure 4f), probably due to the formation of The samples presented an average concentration of SiO 2 of 68.3% and Al 2 O 3 in the order of 16.9%. Both show an inverse trend among them (Figure 4a), as expected, due to their contents in feldspars and micas.…”

“…Thus, some weathering features can be observed in most buildings. This is indicative of two possible explanations: (i) there is a local component of the weathering and processes that cause the formation of stains and coatings, such as local architectural features or façade orientation [2,14,23,24]; (ii) there is some previous inherited weathering of the granites used in the construction of the buildings that must also be taken into account. To clarify these two possibilities, more samples should be studied in the future [8,14,23]…”

“…In general, such effects include a significant loss of valuable building materials, architectural elements and details, considering aesthetic damage (e.g., discoloration) and the definitive loss of material (e.g., detachment, scaling) [11], as it can be observed in sculptural objects of façades, which are sometimes deficient in the conservation conditions of such materials through time [3,12,13]. After decades of studies on monuments around the world [11], it is well known that the decay of stone materials is often a complex phenomenon due to a combination of the natural processes of physical, chemical and biological weathering that can act simultaneously over a long time period, meaning that it is necessary to study Heritage buildings from case to case [14][15][16][17]. Moreover, while the detachment of stone can be very easily observed by the naked eye, other processes such as chemical weathering are difficult to assess.…”

“…Moreover, while the detachment of stone can be very easily observed by the naked eye, other processes such as chemical weathering are difficult to assess. Chemical weathering can affect to the whole stone block, or stone surfaces, sometimes being involved in the growth of stone coatings, discoloration or color changes, as well as the loss of mechanical strength of stones [5,14,18,19] Indeed, coatings can result from biological growth or other physico-chemical processes, and they have been related to stone decay but also stone preservation due to their possible role in the increase in surface hardness [3,14,18].…”