Evidence for crystalline hematite as an accessory phase in Martian soils

Details Evidence for crystalline hematite as an accessory phase in Martian soils Evidence for crystalline hematite as an accessory phase in Martian soils

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992msat.work..134s&link_type=abstract

In Lunar and Planetary Inst., Workshop on the Martian Surface and Atmosphere Through Time p 134-135 (SEE N92-28988 19-91)

Computer Science

Crystallinity, Hematite, Mars Surface, Soils, Amorphous Materials, Color, Emission Spectra, Glass, Mars Photographs, Near Infrared Radiation, Oxidation, Oxides, Spectra

Scientific paper

Based on visible and near-IR spectral images of Mars obtained by us in 1988, we have confirmed the occurrence of bulk crystalline hematite as a minor or accessory phase on the surface. This hematite is not uniformly distributed, being less abundant or absent in certain northern low-albedo regions. Even where most abundant, bulk hematite is not the primary coloring agent of heavily weathered materials on Mars. The primary coloring agent is apparently an amorphous or nanophase Fe3(+) phase, analogous to the coloring agent in certain Hawaiian palagonites (e.g. Adams and Evans, 1980; Singer, 1982; Morris et al, 1989). Based on these results, we can say with considerable certainty that bulk crystalline hematite exists on Mars in small amounts, in addition to the more ubiquitous nanophase or poorly crystalline ferric oxide phase(s). We conclude that Type 2 low-albedo regions (typified by Acidalia Planitia) contain less of this hematite than Type 1 regions (typified by Meridiani Sinus). Oxia Palus shows indication of slightly more oxidation and bulk hematite than Acidalia. This may be a real compositional difference, indicating that Oxia is in some sense transitional between Type 2 and Type 1 regions, but we cannot rule out the possibility of some optical mixing with surrounding higher-albedo regions. We are currently investigating the relationship of ferric-oxides in high-albedo regions to both types of low-albedo regions. As expected, spectral ratios of data from western Arabia to dark regions show considerably greater Fe3(+) in Arabia. There are not obvious spectral indications of a difference in ferric-oxide composition between Arabia and Type 1 low-albedo regions, implying that Arabia also contains minor bulk hematite.

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