Evidence for platy hematite grains in Sinus Meridiani, Mars

Abstract

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.