Characterization, usage and provenance of building rocks in the Fortress of São José of Macapá (Amazon, Brazil)

Abstract

The use of rocks in historical buildings is recurrent, and in the Amazon, it denotes the use of local materials or even those from other continents. In the military fortifications the most usual is the use of easily accessed rocks found in natural outcrops. These structures were pioneered in American cities colonized by Europeans. Historical building restoration involves knowledge of materials and the original quarry sources. With respect to fortresses, is important to understand how rock is used in different functions and treatments. Studying the Fortress of São José de Macapá in Amapá, Brazil, which is exemplary of the 18th century, this paper aims to characterize the rocks in military fortifications according to their architectural applications and their raw material source. For this characterization, mapping and mesoscopic analyses were carried out in association with the analytical techniques of optical microscopy, scanning electron microscopy (SEM) with an analytical system (EDS), X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), and compressive resistance. The results indicated the use of sedimentary rocks and lateritic crusts from the geological environment of the implantation site and its surroundings. However, in the same geological context, they are classified as ferruginized sandstones (FSS), ferruginous lateritic crusts (FLC) and iron stones (IST), all of which are primarily composed of goethite, hematite, quartz and kaolinite. Due to their compositional, textural and physical characteristics, it was possible to correlate their uses and functions in the fortress, which indicated a formal and constructive logic that suited the raw materials available to the builders.