Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..442b&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 442-443
Computer Science
1
Aerodynamic Heating, Cosmic Dust, Fine Structure, Meteoritic Composition, Micrometeorites, Mineralogy, Temperature Effects, Abundance, Antarctic Regions, Atmospheric Entry, Chemical Analysis, Grain Size, Olivine, Porous Materials, Silicates
Scientific paper
The observation of hydrous phases in a micrometeorite from Antarctica has shown that 100-micron-sized cosmic dust particles can enter the Earth's atmosphere with only minor modifications due to thermal processing. In order to obtain compositional information on the preatmospheric mineralogy of fine-grained unmelted micrometeorites, a number of these particles were studied by Transmission Electron Microscopy (TEM). Presently, the least biased samples of micrometeorites were collected in Antarctica. Among the micrometeorites collected in Antarctica a set of unmelted porous or scoriaceous particles exists. In our study these fine-grained particles (50-100 microns in size) comprise about 60% of the total extraterrestrial material. In our study 16 particles were investigated by TEM measurements; most of them primarily consist of small olivines (typically less than 100 nm) with variable Fa contents of 15 to 68 mol%. Less abundant are magnetites, pyroxenes, and glass. Analyses obtained from the interior of the micrometeorite are characterized by low totals compatible with the presence of water-bearing phases. Analyses obtained close to the surface of the particle represent mixtures of anhydrous phases, as indicated by the analytical totals of about 100 wt%. They are probably derived from the decomposition of phyllosilicates due to thermal processing. The presence of phyllosilicates in the interior and of olivines and magnetites close to the surface argues in favor of a thermal gradient throughout hydrous micrometeorites caused by atmospheric heating. The transformation of phyllosilicates into Fe, Mg silicates is well known. The observations in the micrometeorite BI 54 B-4 #9 clearly demonstrate such a transformation during atmospheric entry. Therefore, we assume that phyllosilicate-rich micrometeoroids are most probably common precursors of the fine-grained porous particles primarily consisting of small olivines.
Beckerling W.
Bischoff Addi
Kloeck Wolfgang
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