An ESR study of kaolinite under extreme conditions
Abstract Kaolinite exhibits two principal ESR resonances centred at g ∼4 and g ∼2. Following heat treatment at 500°C, the low-field resonance collapses with a simultaneous increase in intensity of the central line. Similar results were obtained from dry-ground kaolinite and this change is attributed partly to oxidation of Fe 2+ . X-irradiation resulted in new paramagnetic species on the clay surfaces and a corresponding intense signal at g =2, while treatment with solutions of a strong acid and a strong base produced no significant change in the spectrum.