The soapstone present in elements of the cultural heritage of humanity in Congonhas - Brazil: interactions from the quarry to the monuments
Authors: Costa Antônio 
Published: February 2023

The earth is a complex planet in permanent modification and the set of its changes includes the degradation of its stony constituents. These degradations result from the interactions of these constituents with an environment that presents conditions different from those where they were formed and in two-time scales: the geological and the time of man and his projects. About the degradations that occurred over geological time and inside the Earth's crust, we can learn about them from the exposure of stony materials close to the surface, due to uplifts and exhumations resulting from tectonic movements. From the interaction of these materials with these new conditions and, through human interference, the speed of transformation is further increased, whether using extraction, processing, and application techniques. As a result, there is inevitable degradation, which in turn will mean deterioration involving, from contemporary buildings to cultural heritage elements. Situations involving these interactions and their different forms of degradation, whether in extraction or application, can be observed around the world, both in constructions and sculptural sets, produced in stone, and in their respective quarries of origin. In this direction, and as an example, we are bringing information about geological interactions of ultramafic rocks, which underwent transformations inside the Earth's crust, generating steatite. Then, and already in the time of man and his projects, we bring information about the results of interactions of this steatite with the environment from which they were extracted and where they were applied, as in the case of the architectural complex of Congonhas, Brazil, which is a cultural heritage of humanity. As a mineralogical association, these steatites are essentially constituted by minerals such as: talc, serpentine, chlorite, and amphiboles. Subordinately, the presence of carbonates and opaque minerals is observed, all with variable contents. In the case of Congonhas, the carbonate is dolomite, pyrite was the sulphide and magnetite the oxide, often altered to hematite and goethite/limonite. These alterations present in the extraction fronts are very similar to those observed in the elements of the cultural heritage of Congonhas. Both in the quarries and in the applications, the forms of degradation result from rock interactions in geological time and application. Of this set of degradations, those involving chromatic variations, loss of parts by differential erosion with elimination of soft components, by mechanical actions and by dissolution, which in this case involve minerals such as carbonates and opaques, are most visible. Presents are other forms, such as patinas, fissures and biological colonizations. Due to lack of adequate information, mainly involving the dissemination of geological knowledge, as well as participatory approaches with local communities, Congonhas&#8217; heritage is at risk of permanent damage. With the publicity about these degradations, which are progressive, it is expected a greater awareness and measures on the part of the agencies responsible for the conservation of this cultural heritage.