Clay Mineralogical Analysis Using the <0.05-mm Fraction for Forensic Science Investigation—Its Application to Volcanic Ash Soils and Yellow-Brown Forest Soils

Abstract

Abstract Clay mineralogical analysis is conducted with a fraction size of less than 0.05 mm in diameter (<0.05-mm fraction), without extraction of the clay fraction (<0.002 mm), using X-ray diffraction (XRD), infrared absorption (IR), and differential thermal (DTA) techniques. Volcanic ash soils and yellow-brown forest soils were used as samples in this experiment. On the basis of IR spectra, clay mineralogical compositions of volcanic ash soil samples could be classified into four groups. XRD was the most effective to discriminate among the yellow-brown forest soil samples and DTA was sensitive for gibbsite. The following procedure was concluded as the most effective one to discriminate small amounts of soil samples. First, IR is used to classify the samples into an allophane-rich type and a siliceous type. To the former type, DTA is applied, and, to the latter, XRD is applied, followed by DTA. Sample was sufficient for this method, including IR, XRD, and DTA, if about 50 mg of the <0.05-mm fraction was obtained.