The dehydration behavior of a natural cavansite from Poona (India) was investigated by in-situ FTIR and Raman spectroscopy. The thermal induced variations of the water molecule were followed as indicative of the dehydration process. The total mass loss (about 15.12%) occurred at least in four stages viz., 360 K (2.27%), 470 K (6.30%), 560 K (11.31 %) and 760 K (15.11 %). The observed spectral variations indicate that cavansite undergoes a completely reversible dehydration at about 500 K without significant structural changes. It completely dehydrates at around 775 K, above which it is in amorphous phase. Induced spectral variations also indicate that the water molecule coordinated with VO5 group is weakly bonded and detached during early stages of dehydration. (c) 2007 Elsevier B.V. All rights reserved.