Original paper

Stacking defects and long-period polytypes in kaolin minerals from a hydrothermal deposit

Kogure, Toshihiro; Inoue, Atsuyuki


Stacking defects in kaolin minerals (mainly dickite) from a hydrothermal deposit have been characterized using high-resolution transmission electron microscopy (HRTEM) with sufficient image quality to determine the defect structures. A comprehensive correspondence between the stacking sequences for kaolin polytypes belonging to subfamily A and their HRTEM contrasts recorded along the hexagonal ai axes is described. Both disorder of the layer orientations (equivalent to octahedral vacancy sites) and that of the directions for interlayer shift were observed. The probability to form the stacking sequence in which the direction of the interlayer shift and layer orientation in the lower or upper layer are the same is very low but not zero. Long-period polytypic sequences with three- and five-layers periodicities were found. One MDO polytype in the trigonal system with three-layers periodicity was discovered among them. Such long-period polytypes in kaolin minerals are explained by spiral growth with a multilayered ledge, like in micas.


kaolindefectspolytypeshrtemstructure imaging