title: Pigmenting agents in Martian soils: inferences from spectral, Mossbauer, and magnetic properties of nanophase and other iron oxides in Hawaiian palagonitic soil PN-9.
abstract: We have examined a Hawaiian palagonitic tephra sample (PN-9) that has spectroscopic similarities to Martian bright regions using a number of analytical techniques, including Mossbauer and reflectance spectroscopy, X-ray diffraction, instrumental neutron activation analysis, electron probe microanalysis, transmission electron microscopy, and dithionite-citrate-bicarbonate extraction. Chemically, PN-9 has a Hawaiitic composition with alkali (and presumably silica) loss resulting from leaching by meteoric water during palagonitization; no Ce anomaly is present in the REE pattern. Mineralogically, our results show that nanophase ferric oxide (np-Ox) particles (either nanophase hematite (np-Hm) or a mixture of ferrihydrite and np-Hm) are responsible for the distinctive ferric doublet and visible-wavelength ferric absorption edge observed in Mossbauer and reflectivity spectra, respectively, for this and other spectrally similar palagonitic samples. The np-Ox particles appear to be imbedded in a hydrated aluminosilicate matrix material; no evidence was found for phyllosilicates. Other iron-bearing phases observed are titanomagnetite, which accounts for the magnetic nature of the sample; olivine; pyroxene; and glass. By analogy, np-Ox is likely the primary pigmenting agent of the bright soils and dust of Mars.
authors.affiliation: Planetary Science Branch, NASA Johnson Space Center, Houston, TX 77058, USA.
authors.forename: R V
authors.initials: RV
authors.lastname: Morris
authors.forename: D C
authors.initials: DC
authors.lastname: Golden
authors.lastname: Bell JF 3rd
authors.forename: H V
authors.initials: HV
authors.lastname: Lauer
authors.forename: J B
authors.initials: JB
authors.lastname: Adams
mesh_terms: D019419:Evolution, Planetary; D005290:Ferric Compounds / Q000032:analysis; D006254:Hawaii; D018535:Mars; D008854:Microscopy, Electron; D008903:Minerals / Q000032:analysis*; D010316:Particle Size; D012987:Soil / Q000032:analysis*; D015204:Spectroscopy, Mossbauer; D018707:Volcanic Eruptions
chemical_list: D005290:Ferric Compounds; D008903:Minerals; D012987:Soil; C000499:ferric oxide