Revised Methods for Rapid Quantitative Determination of Minerals in Soil Clays

Abstract

Abstract A set of quantitative mineralogical methods was revised and evaluated for routine and rapid mineralogical characterization of clays from southern soils and sediments. The procedures adopted consist of soil dispersion in a pH 9.5 suspension by ultrasonics, centrifuge fractionation to give 300 mg of clay, K‐ and Mg‐saturation by millipore filtration for x‐ray diffraction (XRD), x‐ray emission spectroscopy (XRES), differential scanning calorimetry, and thermogravimetric analyses. Smectite, vermiculite, kaolinite, halloysite, gibbsite, and calcite were quantified from thermal data, hydroxyinterlayered vermiculite and quartz from XRD, using indigenous kaolinite determined by thermal methods as an internal standard, and free iron oxides and mica from XRES analysis. The mean total recovery on 79 samples was 99.9 ± 0.6%. Very good agreement and small average deviations were obtained between mineral quantities determined by these procedures and values reported by other laboratories for several of the same samples. Because the accuracy of the data exceeded most quantitative mineralogical interpretative needs, these methods can be used for routine quantitative mineralogical characterization of most southern soils.