A COMPARISON OF DEHYDRATION PROCESSES OF Al-, Fe

Introdution: Hydrous sulfates (Ca-, Mg-, Fesulfates, and recently Al-sulfates) have been found on Mars by OMEGA (Mars Express orbiter) [1], CRISM (Mars Reconnaissance orbiter) [2], the Spirit and Opportunity rovers [3], and Phoenix lander [4]. Furthermore, the change in hydration degree of Fe 3+ -sulfates after exposed to the current Martian atmospheric condition was suggested by long-duration repeating observations of the Spirit rover [5]. Laboratory experiments on the fundamental properties of hydrous sulfates would help us to link these mission observations to geochemical and hydrological processes that have happened at Martian surface or within the subsurface. A recent study reported the using of a set of dehydration experiments under Mars relevant atmospheric pressure (P), and partial water pressure (PH2O) to derive the dehydration halflife of epsomite (MgSO4.7H2O) at low temperature (T), and suggested a large amount of hydrous Mg-sulfates may still remain within the subsurface on Mars [6]. In this study, we conducted two sets of similar experiments on alunogen [Al2(SO4)3.17H2O] and melanterite [FeSO4.7H2O]; the two sulfates having the highest hydration degrees in their series. These two minerals were observed occurring at terrestrial geological setting, as precipitation products from aqueous solution at middle to low T. The purpose of our study is to compare their dehydration pro-