Crystallographic and mineralogical analyses of quartz extracted from the mine of Terra Branca, Minas Gerais, Brazil

Abstract

In this study, a structural and chemical analysis of quartz from a mine in Terra Branca, Bocaiúva, MG, Brazil was performed. The assay was performed by chemical analysis using XRF, XRD, and Rietveld refinement. In the first two analyses, a high degree of similarity between the samples was found; however, differences were revealed using the Rietveld method. In the latter, it is possible to quantify the degree of perfection of the crystal lattice using its parameters for the unit cell of the crystal. Based on the results discussed above, we can conclude that the hyaline sample has a higher degree of order than the milky quartz sample. This difference is because the unit cell of the milky quartz is more expanded; that is, it has a larger volume, which means that the crystal has deviations from the ideal organization, which can manifest as defects, cracks, and inclusions of air bubbles. The SEM and TEM images also reveal differences between the two samples in terms of morphology. A map of the pore size distribution was also obtained in this study.