Aspectos macroscópicos dos esteatitos encontrados no Santuário Bom Jesus do Matosinhos, Congonhas/MG

Abstract

Meta-ultramafic rocks, here generically called steatites, stand out among those used in the building of The Sanctuary of Bom Jesus de Matosinhos, where they were mostly employed in the production of several ornaments, both in its external and internal portions. Of the whole complex, what stands out the most are the church’s main portal and the churchyard’s twelve statues representing the prophets, which are the object of this study. In this context, this paper seeks to identify and describe macroscopically the steatites employed in these elements, analysing especially their mineralogical, textural and structural differences and similarities. The types described in this corpus of rocks were rich in serpentine or, in other cases, in talc, with their colour ranging from grey to light green. Besides the presence of structures such as layers of various dimensions, some textures that were macroscopically identified indicated the absence of foliation, but also had various degrees of orientation to their mineralogical constituents, and some were anastomosed or even stretched. Texturally, the types found in this study varied among massive, mylonitc and lepidonematoblastic, the latter being distinguished by the orientation of minerals like serpentines, talc, chlorites and amphiboles with a thin to very thin granulation, which sometimes hinders the macroscopic mineralogical identification. The fact that the textural variations in those rocks are so marked can be associated to the structural and mineralogical differences found in the same extraction site or to the possibility of those materials having been extracted from more than a single source. On the other hand, such variations have an impact on the degradation processes verified in this study and, if properly identified, they can contribute for a successful performance of the conservation and restoration works.