Caracterização tecnológica de rochas ornamentais da província Borborema - quartzitos coloridos do Seridó paraibano.

Abstract

The ornamental stones have been used by humanity since the dawn of human civilization, during the Paleolithic/Neolithic period. Due to its aesthetic beauty, the use of marble, granite and other rocks in modern architecture increases every year around the world. The ornamental stone sector (prospecting, producing, extracting and processing) is an industry in constant expansion. Brazil is one of the world's largest players with a broad portfolio comprising granite, slate, serpentinite, metaconglomerates, marble and quartzite, etc. The Southeast and Northeast regions are the main producers, with emphasis on the states of Espírito Santo and Minas Gerais (Southeast) and Bahia, Ceará, Rio Grande do Norte, Paraíba, and Pernambuco (Northeast). This research brings the technological characterization of eight colored quartzite samples (blue, green, gray, light pink, dark pink, white, yellow, and silver) from the region of Junco do Seridó and Várzea, Seridó Paraibano, submitted to the laboratory tests for obtaining its best applicability as a coating. For this purpose, magnetic susceptibility, thermal conductivity, geochemical analysis, petrographic descriptions and integration with data on porosity, ultraviolet radiation, flexural strength at three and four points and uniaxial compression strength were performed. An important parameter for the comfort is the thermal conductivity which one has ranged from 1.91W/ m.K (light pink quartzite) to 4.25 W/m.K (gray quartzite). Petrographic studies have classified this lithotype, as a slightly deformed quartzite, with compositional variations only regarding to the predominance of micas such as lepidolite, muscovite, fuchsite; and occurrences of secondary and accessory minerals such as feldspar, apatite, zircon, epidote, tourmaline, magnetite, calcite, and others. The flexural strength tests at 3 (RF3) and 4 (RF4) points showed higher strengths for gray (43.47MPa@RF3 and 160.65MPa@RF4) and white (22.22MPa@RF3 and 119.83MPa@RF4) quartzites. The smallest measured porosities, 2.90% and 2.70%, were also in these quartzite, gray and white colors, respectively. The structural elements present as prominent schistosity planes and foliation marked the high values obtained in the magnetic susceptibility anisotropy, in silver, white and dark pink quartzites (0.094x10-3 SI, 0.080x10-3 SI and 0.079x10-3 SI, respectively). An ultraviolet radiation, whose simulation evaluated the weathering in the stones, is shown to be high for green, yellow and gray quartzite. Chemical analysis have showed a relationship between silica content and thermal conductivity, with K, Al, Na, Fe being some the most importante elements in terms of concentration and, secondarily; Li, La, Y, Ga, Cs. The uniaxial compressive strength tests revealed greater strength for lithofacies in gray (225MPa) and blue (220MPa) quartzite colors. Based on the results obtained, the quartzites from Junco do Seridó and Várzea have a strong aesthetic bias and would fit as internal and external cladding rocks, however, in the scope of external cladding, their applicability may be limited by geographic location, technical characteristics and severe weather.