Transmission X-ray diffraction of undisturbed soil microfabrics obtained by microdrilling in thin sections

Clay mineralogical studies by X-ray diffraction performed on extracted <2-m u m fractions do not always represent all clay mineral constituents present in the soil. In this work, transmission X-ray diffraction (TXRD) was appli ed to undisturbed microsamples of optically homogeneous mineral soil fabric s and features. These microsamples were isolated by microdrilling their per iphery in soil thin sections, then removing them, and transferring them to glass capillaries for TXRD analysis. The usefulness of this technique for s upplying in situ mineralogical information on identification, structure, an d natural orientation of soil constituents was tested on mineral microfabri cs and features of primary and secondary phyllosilicates. The study demonst rated that TXRD allowed detailed, representative interpretations of undistu rbed mineral features and fabrics. In particular, this technique allowed us (1) to compare mineralogical compositions at selected microlocalities, (2) to study natural preferred orientations, and (3) to detect small amounts o f minor mineral interstratification phases. In addition, complementary info rmation on crystallography and crystal chemistry may be obtained by perform ing analytical transmission electron microscopy on the same microsample.