Abstract
The distinction between kaolinite and metahalloysite occurring in some lateritic soils was examined by electron microscopy, X-ray diffraction method, infrared absorption spectroscopy and thermal analyses. The results are summarized as follows:
(1) In electron micrograph, kaolinite and metahalloysite show the shape of hexagonal plate and tube, respectively. The particle size of soil minerals is smaller than that of geological origins.
(2) The basal spacings of kaolinite are 7.2 and 3.59 Åfor primary and secondary reflection, respectively, while, they are 7.4 and 3.62Åin metahalloysite. The intensity ratios of secondary versus primary reflections are 0.8 for kaolinite and 0.5 for metahalloysite.
(3) The infrared absorption band associated with 0-H stretching vibration of structural hydroxyl groups in kaolinite at the range from 3700 to 3600 cm-1 is split to three or four lines, but that in metahalloysite is split to only two lines. The absorption band associated with Si-0 stretching vibration at the range about 1100 to 1000 cm-1 is also split to three lines in kaolinite and two lines in metahalloysite.
(4) By thermogravimetry and differential thermal analysis, it is difficult to distinguish between kaolinite and metahalloysite.
(5) X-ray diffraction method is most effective to distinguish metahalloysite from halloysite. Therefore, a method of electron microscopy and infrared absorption spectroscopy is appropriate besides X-ray diffraction method for the identification of kaolinite and metahalloysite.
