High-Resolution TEM Investigation of Halloysite

Halloysite has long been regarded as being highly-disordered or even turbostratic structurally. TEM study of halloysite in the past showed little detail in the basal fringes due to rapid beam damage. Most TEM images of halloysite with various morphologies reported in recent literature are at low-magnification. In this study, tubular halloysites from six localities in Australia and New Zealand were intensely examined with HRTEM and electron diffraction using a JEOL 200CX. The results are presented in this paper. Tubular halloysite (Fig. la) HRTEM images recorded show a 7-Å fringe spacing (Fig. lb), which suggests that halloysite has lost its all interlayer water and has collapsed under the high-vacuum conditions in the TEM. The 7-A lattice fringes revealed on the walls of halloysite tubes are similar to those of kaolinite stacks, and exhibit relatively straight layers with fewer defects compared with smectite fringes.