Four Chinese palygorskites clay minerals have been analysed by thermogravimetric analysis-mass spectrometry and X-ray diffraction. The structural water of the palygorskite dehydrates in the temperature range of 30-625 degrees C, as shown in the thermogravimetric analysis and mass spectrometric curves. The mass spectrometric curves combined the differential thermogravimetric curves enable the detailed determination of the main dehydration steps. The results show that the dehydration occurs in four main steps: (a) elimination of interparticle water and partial zeolitic water at below 110 degrees C, (b) release of the rest part of zeolitic water from the structural layer of palygorskite at about 160 degrees C, (c) dehydration of one part of bound water at about 340 degrees C and (d) loss of the rest part of bound water at around 450 degrees C. The temperatures of dehydration of the palygorskite minerals are found to be influenced by the geological environment and the amount and kind of impurities. The evolved gases in the decomposition process are various because of the different amounts and kind of impurities. It is also found that decarbonization takes place at around 600 degrees C due to the decomposition of calcite and dolomite impurities in these minerals. It is evident by the mass spectrometric curve that the water is given out from the samples and carbon dioxide originates from the impurity calcite and dolomite. (C) 2010 Elsevier B.V. All rights reserved.