PRACTICAL DETERMINAT ION OF ALLOPHANE AND SYNTHET IC ALUMINA AND IRON OXIDE GELS BY

A B S T R A C T: X-ray diffraction methods are effective and practical for the quantitative analysis of the often forgotten amorphous material phase in sediments. The method reported is simple, employing normal oriented samples, and quartz or fluorite as a diluent. However, special care must be taken to prepare the samples properly, to ensure optimum conditions for diffraction, and to measure accurately the scattering bands. The classical methods for determining the amorphous inorganic omponents of sediments are based on selective dissolution analysis (Smith & Mitchell, 1984). As these are time-consuming and imprecise, several authors have shown that the nature and the quantity of amorphous components can be determined by X-ray diffraction (XRD) (Bardossy, 1965; Crespo, 1975). Lapaquellerie (1987) proposed a method based on the precise measurement of the scattering band surface representing the amorphous constituent. The method uses mixtures containing different proportions of amorphous material (biogenic silica and volcanic ashes) and crystalline silica to obtain the calibration curves for amorphous silica. These curves have to be determined for several amorphous components and this is difficult for natural materials because these often contain more than one amorphous component