Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..443k&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 443
Computer Science
Iron Meteorites, Iron Oxides, Meteoritic Composition, Meteoritic Microstructures, Weathering, Chemical Analysis, Chile, Crystal Structure, Intergranular Corrosion, Mineralogy, Mossbauer Effect, Oxidation, Shales
Scientific paper
Monturaqui is a meteorite crater, 370 m diameter, in the Andes Mountains, Chile. The surface topography and the state of the corroded meteorite suggest, however, that the climate some time ago must have been more humid. Small fragments of severely corroded iron meteorites have been collected in the vicinity, 50-200 m from the crater rim. Fourteen fragments of iron shale have been examined in order to determine the corrosion products of an entirely disintegrated iron meteorite. Polished sections display some vugs and microporosities and are more than 99.9% oxidic. The nonoxidic parts are minute particles of taenite (38-42 wt% Ni), shcreibersite, rabdite (42 wt% Ni, 0.13 wt% Co, 12.5 wt% P), and cohenite (microhardness 1100 +/- 50). The overall morphology of the oxide shales, which sometimes are of breadcrust type, is that of a coarse octahedrite. X-ray diffractometry on powder samples discloses goethite and maghemite, and occasionally peaks from lepidocrocite and reevesite were identified. Peaks from magnetite, akaganeite, and hematite were not identified. The mineralogy and oxidation state of Fe was also investigated by Fe-57 Mossbauer spectroscopy. Spectra of a representative powder sample were obtained between 16 and 350 K. No indication of purely Fe(II)-containing compounds was present. The dominating components in the Mossbauer spectra are due to maghemite and goethite. The chemistry of the oxides was investigated by microprobe analysis including Fe2O3, NiO, CoO, SiO2, Al2O3, SO3, and Cl in the scheme. The total of the analyses varied from 80.3 to 100.9 wt% with a mean of 87.9 wt%. Despite the relatively simple mineralogy, it is not simple to relate the analyzes to different mineralogies (or mixtures) because of the unknown porosity of the analyzed points and the content of structural hydroxyls in goethite. Point analyses having totals close to 100 may be considered to be dominated by relatively bulky aggregates of maghemite.
Buchwald Vagn F.
Koch Bender Chr.
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