silicon and forsterite

Liquid water is essential to life as we know it on Earth; therefore, the search for water on Mars is a critical component of the search for life. Olivine, a mineral identified as present on Mars, has been proposed as an indicator of the duration and characteristics of water because it dissolves quickly, particularly under low-pH conditions. The duration of olivine persistence relative to glass under conditions of aqueous alteration reflects the pH and temperature of the reacting fluids. In this paper, we investigate the utility of 3 methodologies to detect silicate weathering in a Mars analog environment (Sverrefjell volcano, Svalbard). CheMin, a miniature X-ray diffraction instrument developed for flight on NASA's upcoming Mars Science Laboratory, was deployed on Svalbard and was successful in detecting olivine and weathering products. The persistence of olivine and glass in Svalbard rocks was also investigated via laboratory observations of weathered hand samples as well as an in situ burial experiment. Observations of hand samples are consistent with the inference that olivine persists longer than glass at near-zero temperatures in the presence of solutions at pH approximately 7-9 on Svalbard, whereas in hydrothermally altered zones, glass has persisted longer than olivine in the presence of fluids at similar pH at approximately 50 degrees C. Analysis of the surfaces of olivine and glass samples, which were buried on Sverrefjell for 1 year and then retrieved, documented only minor incipient weathering, though these results suggest the importance of biological impacts. The 3 types of observations (CheMin, laboratory observations of hand samples, burial experiments) of weathering of olivine and glass at Svalbard show promise for interpretation of weathering on Mars. Furthermore, the weathering relationships observed on Svalbard are consistent with laboratory-measured dissolution rates, which suggests that relative mineral dissolution rates in the laboratory, in concert with field observations, can be used to yield valuable information regarding the pH and temperature of reacting martian fluids.

Topics: Elements; Extraterrestrial Environment; Glass; Iron Compounds; Magnesium; Magnesium Compounds; Mars; Microscopy, Electron, Scanning; Porosity; Silicates; Silicon; Silicon Compounds; Spectrum Analysis; Surface Properties; Svalbard; Volcanic Eruptions; Water; Weather

The average value of g factor (i.e., g ) of Cr4+ ions in forsterite (Mg2SiO4) is calculated with the cubic symmetry approximation from the complete high-order perturbation formula of g factor for 3d2 ion in cubic tetrahedral cluster. In the formula, the contribution to g factor from the charge-transfer mechanism (which is neglected in the crystal-field theory) is considered in addition to that from the widely used crystal-field mechanism. From the calculations, the reasonable observed value of g is suggested (note: the experimental values of g by various authors are scattered) and the important contribution of charge-transfer mechanism to g factor can be found.

Topics: Chromium; Crystallization; Electron Spin Resonance Spectroscopy; Electrons; Ions; Magnesium; Magnetics; Models, Statistical; Oxygen; Silicon; Silicon Compounds