The stages and sequence of the reactions between silica-rich natural aluminosilicates and Al in N-2 presence were studied. In this case diatomite-Al-N-2 and bentonite-Al-N-2 reactions were studied up to 1650 degrees C using TG-DTG-DTA and XRD techniques. Thermal effects associated with the nitridation reactions were determined. The final phases formed were sialon-alumina mixtures with silicon and aluminium nitride as important intermediaries. The phases formed were the same as those predicted by the Si-Al-O-N phase diagram.