Evidence for a Hematite Mineral Deposit on Mars

ABSTRACT
Midinfrared spectral data received from the Mars Global
Surveyor Thermal Emission Spectrometer (MGS-TES) instrument
indicate the presence of a large deposit of hematite (a-Fe2O3) in
Sinus Meridiani, Mars. This hematite deposit, that is accompanied
by basalt, encompasses an area ~350 by 500 km.
To understand the geologic context of this large hematite mineral
occurrence, a detailed laboratory spectroscopic investigation
was conducted using more than 25 terrestrial hematite samples so
that their spectra could be compared to the hematite spectrum of
Sinus Meridiani (SM). The samples represented a wide variety of
physical properties and included red and gray polycrystalline hand
samples, gray single-crystal hand samples, and red and gray fineand
coarse-grained particulates. The laboratory analyses provided
thermal emissivity spectra that, when compared to the hematite
emissivity spectra from Mars, suggest the SM hematite is possibly
an exposure of oriented hematite grains. These grains are likely
coarser that 10 mm (and may be much larger) and gray in color. The
characteristic of oriented grains is suggested by the apparent crystal
axis-dependence of the energy emitted from the surface of Mars.
The strong degree of crystal alignment exhibited in the emissivity
spectra of the SM hematite suggests that it occurs either as outcrops
comprised of aligned specular hematite grains (schistose texture), as
well-aligned platy particles, or as a rock rind. We favor the SM
hematite to be schistose rock, and suggest that it originated as a
chemical precipitate in an early body of water that was later buried,
recrystallized and grain-oriented, then subsequently reexposed.