Importance of Sample Pretreatment for X‐Ray Diffraction and X‐Ray Fluorescence of River Sand

ABSTRACT The river sands from the Sakawa River Basin, Kanagawa Prefecture, Japan were characterized by X‐ray diffraction (XRD) and X‐ray fluorescence (XRF) analyses. The river sand samples were subjected to heavy‐liquid separation using a sodium polytungstate solution to separate heavy and light minerals for XRD analysis. In addition, the river sand samples and the mineral samples were melted with lithium tetraborate to prepare glass beads for XRF analysis. Five types of heavy minerals—hornblende, epidote, olivine, augite, and hypersthene—were identified in the XRD patterns of the river sand samples, and four types of river sands were differentiated based on heavy‐mineral assemblages. The composition of plagioclase, that is, the anorthite (An) mole percent content, in the river sand samples was determined using XRD and XRF. The composition of plagioclase in the river sands ranged from An 41 mol% to An 86 mol%, and two river sands with similar heavy‐mineral assemblages were differentiated by their plagioclase composition. A principal component analysis (PCA) was performed using the concentrations of 10 major elements (Na, Mg, Al, Si, P, K, Ca, Ti, Mn, and Fe) obtained by XRF. Based on the results of PCA, the two river sands with similar heavy‐mineral assemblages and plagioclase compositions were differentiated. In this study, we differentiated eight river sand samples collected from the Sakawa River Basin based on (1) heavy‐mineral assemblage, (2) plagioclase composition, and (3) PCA.