Built cultural heritage of Ouro Preto, Brazil: an architectural legacy edified in quartzite stone

The city of Ouro Preto, located in Minas Gerais, Brazil, a cultural heritage of humanity since 1980, has still preserved within its listed urban site, buildings built from the 18th century, when Brazil was still a Portuguese colony. In a geological context, it is certain that the city grew in the middle and is surrounded by mountain ranges formed by quartzite crests with some occurrence of schist and steatites in the regions of its valleys. Based on comparisons with other regions of the country, it can be stated that due to this particular geodiversity, the city stands out even from others in Minas Gerais, due to the volume and diversity of quartzite material used in its buildings. The architectural ensemble that served as the basis for the granting of the title by Unesco includes buildings and monuments with public, religious and private purposes, which make up a legacy of importance for the history of Minas Gerais and Brazil. The set built using quartzite material, however, inspires attention, since the artisanal process of extracting and processing the pieces did not take into account properties suitable for applications, which until then were little known. Taken from known areas around the city and located in the mountains known as Ouro Preto and Itacolomy, it appears that the process did not involve steps and procedures that are typical of quarries, especially those we know today. These rocks were, for the most part, collected both in the form of blocks and plates, later undergoing some kind of processing. The blocks were widely used as structuring elements, such as pillars and columns, door and window frames and the plates, used in external and internal coatings. With some frequency, blocks were also used in decorative elements in masonry, such as portals on church facades and even in sculptural art, with the production of elements that make up various building facades such as, for example, the former Chamber and Prison House, currently headquarters of the Museum of the Inconfidence. With a greater or lesser degree of detail, these works can also be seen in the nineteen churches and chapels inserted in the listed perimeter. Sculptural elements are also present in a good part of the various fountains built in different parts of the old city, among them, six individually listed and whose objective was to facilitate the supply of water to the city. With some rarity, compositions involving the use of schists and steatite in decorative arrangements with quartzites are observed. It is understood that the survey of information on the former extraction areas of these rocks, on the various types of applications and on the buildings that are part of this architectural set, as well as on their deterioration processes, will be of importance to support conservation actions of this cultural heritage.