Salts with high hydration states have the potential to maintain high levels of relative humidity (RH) in the near subsurface of Mars, even at moderate temperatures. These conditions could promote deliquescence of lower hydrates of
ferric sulfate,
chlorides, and other
salts. Previous work on deliquesced ferric
sulfates has shown that when these materials undergo rapid
dehydration, such as that which would occur upon exposure to present day Martian surface conditions, an amorphous phase forms. However, the fate of deliquesced halides or mixed
ferric sulfate-bearing brines are presently unknown. Here we present results of rapid
dehydration experiments on Ca-, Na-, Mg- and Fe-
chloride brines and multi-component (Fe2 (SO4)3 ± Ca, Na, Mg, Fe, Cl, HCO3) brines at ∼21°C, and characterize the
dehydration products using visible/near-infrared (VNIR) reflectance spectroscopy, mid-infrared attenuated total reflectance spectroscopy, and X-ray diffraction (XRD) analysis. We find that rapid
dehydration of many multicomponent brines can form amorphous solids or solids with an amorphous component, and that the presence of other elements affects the persistence of the amorphous phase under RH fluctuations. Of the pure
chloride brines, only Fe-
chloride formed an amorphous solid. XRD patterns of the multicomponent amorphous
salts show changes in position, shape, and magnitude of the characteristic diffuse scattering observed in all amorphous materials that could be used to help constrain the composition of the amorphous
salt. Amorphous
salts deliquesce at lower RH values compared to their crystalline counterparts, opening up the possibility of their role in potential deliquescence-related geologic phenomena such as recurring slope lineae (RSLs) or soil induration. This work suggests that a wide range of aqueous mixed
salt solutions can lead to the formation of amorphous
salts and are possible for Mars; detailed studies of the formation mechanisms, stability and transformation behaviors of amorphous
salts are necessary to further constrain their contribution to Martian surface materials.