Abstract
A kaolin mineral in the form of long fibres, similar to the fibrous kaolin from Brazil (de Souza Santoset al., 1965), was found in the a= 7·056 andc= 9·730 Å, and was confirmed by electron diffraction from selected grains. Evidence of chemical composition was obtained by XRF and IR spectrometry. Bastnaesite can be mistaken for gibbsite because their strongest reflections have nearly the same spacing,d= 4·85 Å, when unheated oriented specimens are used. The occurrence of bastnaesite indicates that it is formed when the rock weathers, but is unstable in the soil.