Chemical and mineralogical changes in the textural fractions of quartzite-derived tropical soils, along weathering, assessed by portable X-ray fluorescence spectrometry and X-ray diffraction

Abstract

The variability of mineralogical and chemical characteristics of soils reflects their parent material, the different weathering degrees and soil formation processes. Through the association of portable X-ray fluorescence (pXRF) spectrometry and X-ray diffraction (XRD), this work aimed to evaluate the concentration of major and minor elements and their relationship with the mineralogy of the sand, silt and clay fractions in a catena of soils derived from quartzite with different weathering degrees in Southern Minas Gerais State, Brazil. Five soil profiles were described and sampled: Lithic Ustorthent, Typic Ustorthent, Typic Dystrustept, Xanthic Haplustox, and Typic Ustifolist. Sand, silt and clay fractions were separated and analyzed with pXRF and XRD for characterization of elemental contents and mineralogy, respectively. For all soils, Si content was higher in the sand fraction, corresponding to quartz, confirmed by XRD, a predominant mineral in quartzite and in the sand fraction of tropical soils. Al content was always higher in the clay fraction, reflecting the presence of kaolinite, gibbsite and mica. Quartz, mica and kaolinite were the dominant minerals in the silt fraction. Si in the sand fraction showed a strong and negative correlation with K and Ca, while Al in the sand fraction showed high and positive correlations with Ca and Fe. Fe, K, Ca and Al were released from the most weathered soils, while Si remained almost constant due to its large presence in quartz. The pXRF in tandem with XRD provided in-depth clarifications on the chemical and mineralogical differentiation of the sand, silt and clay fractions of soils along weathering.