Quantitative Clay Mineralogical Analysis of Soils and Sediments
The objective of this paper is to present flow sheets for a system of quantitative minera-logical analysis of clays of soils and sediments and to show representative results. Selective dissolution analysis by the Na2S2O7-HCl-NaOH procedure yields the quartz and feldspar contents (0 to 63%) and differentiates feldspar K from mica K. The NaOH-thermal system of selective dissolution yields the allophane plus gibbsite, kaolinite plus halloysite, and dickite contents (0 to 84% for the sediments; 1 to 25% for soil clays) Mica contents (0 to 92% for the rock specimens, 7 to 43% for soil clays) are determined by nonfeldspathic K (and Na). Vermiculite contents (1 to 97% of specimens; 3 to 21% for soil clays) are measured by blocking of interlayer CEC by drying at 110°C while K saturated and replacing with NH4Cl. Montmorillonite (and palygorskite) contents (0 to 85% of specimens; 3 to 36% of soil clays) are determined by the CEC not blocked by the K and NH4 sequence for vermiculite. Chlorite contents (0 to 85% for specimens; 0 to 37% for soil clays) are determined by thermal gravimetric analysis, after allocation of OH water lost between 300 and 950°C to other hydrous minerals determined.
The best evidence of the accuracy of the system of analysis lies in the consistent total recovery of 24 standard mineral samples averaging 100.4 ± 1.3 (± standard error of means) and of 22 soil clay samples averaging 99.5 ± 0.8. The different constituents were present in widely different proportions in the various samples, and were determined by independent methods. The complementary total of near 100% (maximum range 95 to 105% for specimens; 95 to 103% for soil clays) for the analyses is a significant measure of the specificity of the several determinations.
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