Evidence for platy hematite grains in Sinus Meridiani, Mars

Midinfrared (∼1600-200 cm^-1) spectral data received from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) have provided evidence for a large hematite-bearing (α-Fe₂O₃ deposit in Sinus Meridiani, Mars. We report here the results of a laboratory spectroscopic investigation of 24 hematite samples, including polycrystalline hand samples (massive and schistose textures), single-crystal hand samples, and particle-size fractions (single-crystal and polycrystalline discrete particles). Laboratory midinfrared analyses of crystallographically oriented hematite samples suggest that the hematite emission in Sinus Meridiani (SM) is predominantly from the crystallographic c-face of hematite. This observation implies the presence of platy hematite particles, with the plate face being the crystallographic c-face. The observations are consistent with a formational model where the platy, gray hematite originated as an iron-oxide, chemically precipitated from Fe-rich aqueous and/or hydrothermal solutions on early Mars, that was buried, recrystallized to platy hematite, and subsequently reexposed as lenses of schistose hematite in a friable, consolidated stratigraphic unit. Unconsolidated platy hematite particles are also likely to be present as a physical-weathering product of the schistose hematite lenses.