Spatial distributions of secondary minerals in the Martian meteorite MIL 03346,168 determined by Raman spectroscopic imaging

Abstract

AbstractMiller Range (MIL) 03346 is a nakhlite meteorite that has been extensively studied due to its unique complex secondary mineral phases and their potential implications for the hydrologic history of Mars. We conducted a set of Raman spectroscopic and Raman imaging studies of MIL 03346,168, focusing on the secondary mineral phases and their spatial distributions, with a goal to better understand the possible processes by which they were generated on Mars. This study revealed three types of calcium sulfates, a solid solution of (K, Na)‐jarosite and two groups of hydrated species with low crystallinity (HSLC) in the veins and/or mesostasis areas of the meteorite. The most abundant Ca‐sulfate is bassanite that suggests two possible paths for its direct precipitation from a Ca‐S‐H2O brine, either having low water activity or with incomplete development (producing bassanite with gypsum microcrystals) on Mars. The second most abundant Ca‐sulfate is soluble γ‐CaSO4 which raises a new question on the origins of this phase in the Martian meteorite, since γ‐CaSO4 readily hydrates in the laboratory but is apparently stable in Atacama Desert. The close spatial relationship of (K, Na)‐jarosite solid solutions with rasvumite (KFe2S3), magnetite, HSLC, and fine‐grained low‐crystallinity alkali feldspar in mesostasis suggests a potential in situ formation of mesostasis jarosite from these Fe‐K,Na‐S‐O‐H2O species.