Infrared Studies of Ni-bearing Clay-minerals of the Kerolite-pimelite Series

Abstract--Two kerolite and one garnierite samples were subjected to progressive heat reatments prior to their examination by infrared spectroscopy (IR) in the 1200-600-cm-1 and 3800-3000-cm-1 regions. The heat reatment ofthe garnierite (a mixture of nepouite and pimelite) selectively dehydroxylated the nepouite thus allowing an examination to be made of the OH-vibration bands due to the pimelite. Both the relative intensities of the 710-670-cm-1 doublet and of the different OH-stretching bands indicated the Ni content of this pimelite to be about 70%. The heat reatments did not modify the 1200-600-cm 1 region of the spectra of kerolites but caused a noticeable sharpening inthe OH-stretching region. The relative intensities of the structural OH-stretching bands of dehydrated kerolites showed that they differ from Ni-talcs of similar composition i the distribution of Ni and Mg in the octahedral sites. These cations are randomly distributed in Ni-talc but are mainly segregated into Mg and Ni domains in kerolite. Changes in sharpness, intensity, and position of the structural OH-stretching bands of the kerolites as temperature increases and dehydration progresses are similar to those undergone by Mg- or Li-saturated trioctahedral smectites, Also thermal analysis curves of these minerals how similarities with those of Mg- and Ni-saturated smectites, and sug-gest that in kerolites too, the hydration water is associated with interlayer (though non-exchangeable) Ni and/or Mg cations

An Occurrence of Interstratified Kaolinite-smectite Minerals in a Red-black Soil Toposequence

ABSTRACT: Interstratified kaolinite-smectite minerals form the major part of a pedon transitional between 'red ' kaolinitic and black smectitic soils in a soil toposequence derived from basalt in Burundi, Central Africa. These interstratified kaolinite-smectites have many X-ray, morphological and chemical features incommon with 'tabular halloysite'. Modifications tothe 001 spacings of these minerals brought about by thermal nd chemical treatments, however, show that they are not halloysite but consist of a mixture of ~ 70~o kaolinite and 30~o smectite randomly interstratified. Field evidence indicates that hese clays can be considered asa transient stage in the overall reaction smectite--,kaolinite + ron oxides, which takes place in this landscape whenever the slope gradients give rise to better drainage conditions. When Wilson & Cradwick (1972) reported the first occurrence of interstratified kaolinite-smectite n soils, they suggested that, as X-ray criteria for identifying such clays had now been made available, further accounts of such occurrences could be expected. Although several subsequent papers described similar minerals occurring in sediment