Electron Micrographic Studies of Clays
In order to provide a set of reference photographs to be used in identification studies, electron micrographs at relatively high magnification (40,000 to 132,000 diameters), together with some electron diffraction patterns, have been obtained of a group of (a) kaolinites, (b) halloysites, and (c) South Texas outcrop soil samples. Some of the kaolinites consist of well-formed hexagonal crystal plates with edges still sharp at a magnification of 132,000 diameters. Other kaolinites consist of irregular, relatively thin crystal sheets, which may be bent or folded. In one instance it has been possible to demonstrate that the average thickness of the sheets is only 10 Å. At high magnification the halloysite clay minerals exhibit a structure consisting of rolled sheets, rather than hollow rods. In some cases, it is evident that several separate crystal sheets are coaxially rolled to form multiple concentric hollow tubes. In the South Texas outcrop samples, the morphology is very complex, as the samples do not consist of one uniform type of particle. Matted sheets composed of interlaced bundles of lath-like particles have been observed. These oriented particles exhibit typical “fiber” type electron diffraction patterns. Kikuchi lines were observed in a thin quartz crystal plate, examined for comparative purposes.
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