Fe-sulfate minerals are commonly formed by oxidation of pyrite (FeS2) and the following evaporation/crystallization. A variety of factors contribute to the stability of the products of this process, including temperature, redox conditions, pH, and relative humidity. This study focuses on the effect of relative humidity on formation of these minerals. Locations rich in Fe-sulfates can be found on Earth in areas of acid mine drainage. These systems release acidity and toxic metals, causing environmental damage. Understanding the complex chemical processes behind acid mine drainage could give insight into more effective ways to treat it. Analysis of soil on the Martian surface has also revealed a high level of sulfate minerals, especially Fe-sulfate minerals. It appears that they are not formed through pyrite oxidation, but rather through the interaction of acid with iron-rich rocks. Relative humidity varies greatly on the Martian surface, and therefore similar transitions are expected to happen there as well, linking these two environments.

The main goal of our research is to investigate the stability of these Fe-sulfate minerals, mainly as a function of relative humidity. The first step is the synthesis and isolation of a variety of sulfate minerals, all occurring in acid mine drainage environments and found or inferred to occur on the Martian surface. As relative humidity also affects the evaporation/crystallization of these minerals, it will be monitored during this stage as well. The synthesized material will then be examined in situations of varying relative humidity. X-ray diffraction will be used to characterize the samples both in-situ and after time in a humidity-buffered environment.