X-RAY-DIFFRACTION ANALYSIS OF THIN CLAY FILMS FROM DILUTE SUSPENSIONSUSING GLANCING INCIDENCE DIFFRACTION

X-ray diffraction (XRD) analysis of small quantities of clay mounted o n glass slides using conventional Bragg-Brentano geometry generally pr oduces unsatisfactory low intensity reflections masked by amorphous su bstrate scatter. Glancing-incidence asymmetric Bragg diffraction, an a lternative uncoupled geometry, uses a fixed low-incidence angle and pa rallel-beam optics to increase path length through the sample and decr ease X-ray penetration into the substrate. To evaluate this technique on thin soil clay films, results from conventional Bragg-Brentano and glancing-incidence diffraction (GID) were compared for progressively d iluted clay suspensions separated from 2 southeastern soils with typic al mineral assemblages. Patterns produced by GID showed overall higher reflection intensities and reduced substrate scatter, especially at h igher 2 theta angles within the amorphous glass region. Using GID, pos itive identification of clay minerals was obtained from sample quantit ies as small as 0.005 mg cm(-2) and suspensions as dilute as 29 mg L-1 .