Two evaporite minerals fro the El Jaroso Ravine, Spain have been analysed by thermogravimetry coupled with an evolved gas mass spectrometer. X-ray diffraction results proved the evaporite minerals were a mixture of sulphates including the minerals magnesiocopiapite, coquimbite and possibly alunogen. Thermal decomposition of the unoxidised samples showed steps at 52, 99, 143 degrees Celsius confirmed by mass spectrometric results and attributed to adsorbed water, interstitial water and chemically bonded water. This evaporite mineral rock showed two higher temperature decomposition steps at 555 and 599 degrees Celsius with mass losses of 19.6 and 7.8%. Slightly different temperatures for the thermal decomposition of the oxadada sample were observed at 52, 64.5 and 100 degrees celsius. Two higher temperature mass loss steps at 560.5 and 651 degrees Celsius were observed for the oxidised sample. By comparison of the thermal analysis patterns of halotrichite and jarosite it can be shown that the El Jaroso samples are mineral sulphates and not halotrichite or jarosite.