Differential thermal analysis and thermogravimetry have been used to compare the dehydration and dehydroxylation behaviour of a series of nontronites including two newly discovered nontronites from Uley, South Australia. A comparison is made with the thermal behaviour of ferruginous smectite. Three dehydration endotherms were found at around 60 degrees C, 100 degrees C acid 160 degrees C. A strong dehydroxylation endotherm for all samples was found at similar to 430 degrees C. The nontronites from Hohen-Hagen and Garfield show well-defined steps for dehydroxylation whereas the two Uley nontronites showed continuous dehydroxylation. The intensities of the infrared spectra of the hydroxyl-stretching region showed excellent correlation with the nontronite dehydroxylation endotherms. The infrared spectra of the water bending region showed two bands centred at similar to 1630 and 1670 cm(-1). These bands are attributed to adsorbed water and coordinated water.