Genetic Significance of Paramagnetic Centers in Kaolinites
Paramagnetic impurities, Fe3+, Mn2+ and vanadyl (VO2+) ions, along with paramagnetic radiation-induced defect centers, trapped holes, have been investigated with electron paramagnetic resonance (EPR) in more than 350 kaolin samples from different localities. The trace elements determined are either substituted (Fe3+) or adsorbed (Mn2+ and VO2+). The thermal stability of the radiation-induced defects has been determined. The genetic significance of the EPR spectra has been considered on the basis of previous data from the literature and new informations obtained in this study. It is shown that paramagnetic centers: (1) can be used to differentiate kaolinites from the three major environments at the Earth’s surface, hydrothermal, weathering and sediments; (2) are indicators of growth conditions of kaolinite; (3) provide a basis for interpreting conditions of kaolinite formation in different environments; and (4) fingerprint accurately several stages of kaolinite growth and/or successive geochemical events.