The water uptake and release by perchlorate salts have been well studied since the first in situ identification of such salts in the Martian soil by the Phoenix mission in 2008. However, there have been few studies on the effect of the insoluble regolith minerals on the interaction of perchlorate with water vapor. In this work, we investigate the impact of a Mars-relevant mineral, montmorillonite, and a Mars soil analog, Mojave Mars Simulant (MMS), on the deliquescence (transition from dry crystalline to aqueous via water vapor absorption), ice formation, and efflorescence (transition from aqueous to dry crystalline via loss of water) of pure magnesium perchlorate. We studied mixtures of magnesium perchlorate hexahydrate with either montmorillonite or MMS. Although montmorillonite and MMS are materials that may serve as nuclei for either ice nucleation or salt efflorescence, we find that these soil analogs did not affect the phase transitions of magnesium perchlorate. The salt-mineral mixture behaved similarly, within estimated uncertainties, to pure magnesium perchlorate in all cases. Experiments were performed in both N 2 and CO 2 atmospheres, with no detectable difference. We use data from the Mars Science Laboratory Rover Environmental Monitoring Station instrument and the Phoenix Thermal and Electrical Conductivity Probe, as well as modeling of the shallow subsurface, to determine the likelihood of these perchlorate phase transitions occurring at Gale Crater and the northern arctic plains (Vastitas Borealis). We find that aqueous solutions are predicted in the shallow subsurface of the Phoenix landing site, but not predicted at Gale Crater. Plain Language Summary Most previous studies on Mars-relevant salts have looked at the water uptake and release of the pure salts, but few have looked at the effect that insoluble minerals might have on the water uptake and release. This is an important potential effect because the surface of Mars is mainly composed of (~99%) mineral dust and we might not be accurately predicting if liquid solutions are possible on Mars today. However, this study shows that a Mars-relevant mineral (montmorillonite) and a Mars surface analog (Mojave Mars Simulant) did not have a significant effect on the water uptake of magnesium perchlorate. In addition, the Phoenix landing site is more favorable to support liquid solutions of magnesium perchlorate, rather than Gale Crater (Curiosity's current site).

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Structural parameters and their thermal changes in natural magnetite, Fe3O4, have been studied using the single-crystal X-ray diffraction method in the temperature range 126–773 K. The cell dimensions, oxygen coordinate and atomic mean square displacements (m.s.d.'s) reversibly change as a function of temperature. The coordinate of oxygen remains almost constant at x = 0.2549 (1) below ~600 K, but increases with increasing temperature above this temperature. This characteristic behavior of the oxygen coordinate with temperature indicates that the cation disordering over the tetrahedral (A) and octahedral (B) cation sites occurs above 600 K. All atomic m.s.d.'s increase monotonously with temperature rise. The m.s.d.'s of the B atom show a unique temperature dependence. At lower temperatures the B atom prefers to vibrate along [111], but this preference is reduced with a temperature rise up to 630 K, above which the m.s.d. normal to [111] becomes dominant.

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Unit cell parameters, Raman scattering profiles and DTA curves were measured on monoclinic tridymite from fired silica brick. Ten peaks appear in the Raman measurements from 100 to 1250 cm 1 at 25 C, and their positions and widths show no significant change up to 110 C. The monoclinic unit cell parameters, a, b, c and , slightly increase or remain nearly constant with increasing temperatures up to 110 C. Both the Raman spectra and the unit cell parameters undergo significant changes in the range from 110 to 115 C. Only two endothermic peaks, at 117 and 166 C, appear in the DTA curve measured on a powdered sample of nearly pure monoclinic phase in a heating run from 25 to 300 C. In X ray single crystal refinements, the structural parameters including anisotropic temperature factors of atoms were fully determined for the monoclinic phase at 25, 80, 90 and 100 C, and the orthorhombic phase at 140 C. The difference between the temperature factors on both sides of the transition point is the most remarkable: 0.0286 A 2 in average for all O atoms at 100 C in the monoclinic phase and 0.0713 A 2 at 140 C, both for B eq . The averaged Si O distances calculated for the atomic mean positions decrease with increasing temperatures: 1.599 A at 25 C, 1.595 A at 100 C and 1.576 A at 140 C, whereas the values corrected for the thermal displacement parameters remain unchanged at 1.61 A through all the temperatures studied.