Abstract
A white powdery clay mineral with 28.8Å. spacing was found in the kaolinite vein of the Uku mine, Yamaguchi Prefecture. The interplaner spacings of stronger X-ray powder diffraction lines of the mineral are as follows: 28.8±0.1, 14.5±0.1, 4.82±0.02 and 1.4893±0.0005Å.. The 14.5Å. line shifts to 15.4±0.2Å. and the 28.8Å. line is persistent in the temperature range from 20° to 300°C., but completely disappears above 400°C.. The 14.5Å. line is replaced by the 12.4Å. line at 400°C.. which is persistent up to 600°C. but disappears above 700°C. At 1200°C. the specimen is transformed to mullite.
It is considered that, as T. Sudo et al. have already pointed out, the unusually long spacing of 28.8Å. is the result of a regularly alternating stacking of two kinds of layer lattices; one is the ordinary montmorillonite lattice with the basal spacing of about 14.8Å. and the other is a hypothetical aluminium chlorite lattice with the basal spacing of about 14.0Å..
