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Moessbauer spectra of olivine-rich achondrites - Evidence for preterrestrial redox reactionsMoessbauer spectral measurements at 4.2 K were made on several ureilites and the two shergottites found in Antarctica, as well as two ureilite falls, three SNC meteorite falls, and two finds in order to distinguish products of preterrestrial redox reactions from phases formed during oxidative weathering on the earth. The spectra indicated that several ureilites contain major proportions of metallic iron, much of which resulted from preterrestrial carbon-induced reduction of ferrous iron in the outermost 10-100 microns of olivine grains in contact with carbonaceous material in the ureilites. The cryptocrystalline nature of these Fe inclusions in olivine renders the metal extremely vulnerable to aerial oxidation, even in ureilites collected as falls. It is inferred that the nanophase ferric oxides or oxyhydroxides identified in Brachina and Lafayette were produced by terrestrial weather of olivines before the meteorites were found. The absence of goethite in two olivine-bearing Antarctic shergottites suggests that the 2 percent ferric iron determined in their Moessbauer spectra also originated from oxidation on Mars.
Document ID
19910057730
Document Type
Conference Paper
Authors
Burns, R. G. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Martinez, S. L. (MIT Cambridge, MA, United States)
Date Acquired
August 15, 2013
Publication Date
January 1, 1991
Subject Category
LUNAR AND PLANETARY EXPLORATION
Meeting Information
Lunar and Planetary Science Conference(Houston, TX)
Funding Number(s)
CONTRACT_GRANT: NAGW-2037
CONTRACT_GRANT: NSG-7604
CONTRACT_GRANT: NAGW-1078
Distribution Limits
Public
Copyright
Other