抄録
Natural growth faces and cleavages of kaolinite crystals were characterized by electron microscopy using a gold decoration method. The cleaved surfaces of kaolinites treated with urea followed by wet-grinding showed slip steps but not growth spirals, whereas the surfaces of kaolinites etched with NH4F showed growth spirals. Therefore, the surface microtopographs of kaolinites with different crystallinities from deposits and soils were compared before and after etching with NH4F. Well-crystallized kaolinites from hydrothermal deposits exhibited growth spirals with wide spacings, irrespective of whether they were etched with NH4F or not, and were characterized by spiral growth from solution phase of low supersaturation. Poorly-crystallized kaolinites from sedimentary deposits showed growth spirals on the surface etched with NH4F but not on the original surface. The concentration of NH4F solution suitable for removal of the surface layers of kaolinite crystals was 5 to 15 %. The relationships between the crystallinity and the type of growth spirals observed before and after etching with NH4F were similar for kaolinites from residual soils other than one transported soil and kaolinites from deposits. The differences in environmental conditions of their formation were discussed.
