PARTICLE-SHAPE VERSUS COHERENT SCATTERING DOMAIN OF ILLITE SMECTITE -EVIDENCE FROM HRTEM OF DOLNA-VES CLAYS/

Fundamental Particle thickness measurements of Doing Ves hydrothermal illite/smectite (I/S) samples confirmed earlier findings regarding the content of fixed cations in illite interlayers (ca. 0.9/O-10(OH)(2)). The distributions of fundamental particles and mixed-layer crystals o f a given sample are internally consistent. In samples dominated by bi layer fundamental particles, mixed-layer crystals most often contain e ven numbers of layers. The expandabilities measured by XRD are much hi gher than so-called minimum expandabilities obtained from HRTEM measur ements. This discrepancy is explained by assuming that the coherent sc attering domains of Dolna Ves clays do not correspond to natural mixed -layer crystals but are thicker, probably due to parallel association of crystals on the oriented XRD slide. This tendency to produce interc rystal contacts is probably related to the unusually large ab dimensio ns of crystals of Dolna Ves clays.