Two kaolinitic clays were selected for this studyone low-Fe clay (1.1 wt.% Fe2O3), and one Fe-rich clay (24.4 wt.% Fe2O3) (Table ). The chemical oxide composition of the clays was measured by X-ray fluorescence (XRF) spectroscopy (Table ), using a Rigaku ZSX Primus II, with the fused bead preparation method and a loss on ignition (LOI) heating step carried out at 900°C for 2 hours.