Quantitative Measurement of Paramagnetic Fe3+in Kaolinite

A method is proposed to measure the absolute concentration of paramagnetic Fe3+ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+signal is calibrated by calculating the powder EPR spectra of Fe3+ions in corundum and low-defect kaolinite. The paramagnetic Fe3+concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ions and other iron species, such as Fe3+concentrated phases and Fe2+ions. The concentration of isolated structural Fe3+ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.