Abstract
It has been found that aspidolite, the Na analogue of phlogopite, has an unusual interlayer structure for micas. HRTEM and electron diffraction analyses indicate a large layer offset, i.e., lateral shift between the two tetrahedral sheets across the sodium-bearing interlayer region. The amount of the layer offset is about 0.09 nm (ca. a/6) and the direction is one of [-100], [110] and [1-10]. By combination of the intralayer shift and layer offset, the ordered aspidolite has different one-layer structures with monoclinic and triclinic cells. Both structures were identified in powder X-ray diffraction patterns. This is the first report that structural variations are generated in micas by the combination of the intralayer shift and layer offset.
