Raman Spectroscopy - a Study of Iron Sulfate Minerals: Raman Spectroscopic Study of Ferrous Sulfate Hydrates and Jarosites

Raman spectroscopy has been used to study hydrous sulfate minerals of importance to planetary science. These minerals are the mono-, tetra- and heptahydrates of ferrous sulfate and minerals of the jarosite group including Na-, K- and NH4-jarosite. Each mineral has its characteristic spectrum that can be used for remote identification on planetary surfaces and is important in the study of past geological environment. Effects from the waters of crystallization and hydrogen bonding on the Raman spectra of ferrous sulfate hydrates have been studied. Structural changes and phase transitions in these hydrates under cryogenic temperatures and high pressures have been studied. In the study of jarosites, the variations observed in the Raman spectra at room temperature and cryogenic temperatures are discussed in terms of changes in unit cell dimensions influenced by different interlayer cations. The Raman and IR spectra of K-jarosite after heating to 230 and 400 °C showed the presence of yavapaiite, which was also detected in the Raman spectra of K-jarosite at room temperature under reduced water vapor pressure in conditions that can be found on the surface of Mars.