Mathematics – Logic
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.518p&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 518-519
Mathematics
Logic
Achondrites, Iron Compounds, Magnesium Compounds, Meteoritic Composition, Meteoritic Microstructures, Olivine, Chemical Composition, Fractures (Materials), Lamella (Metallurgy), Mineralogy, Transmission Electron Microscopy
Scientific paper
The Divnoe meteorite is a granoblastic olivine-rich primitive achondrite whose textural and mineralogical characteristics suggest extensive recrystallization during slow cooling in the temperature range from approximately 1000 to approximately 500 C and lower. Olivine grains in this meteorite show a lamellar appearance in BSE images, caused by minor micrometer-scale chemical variations in Fe, Mg, and Mn contents between adjacent lamellae. Ten grains of lamellar olivine were studied in detail by Electron Probe Microanalysis (EPMA) and optical microscopy and two of these by Transmission Electron Microscopy (TEM). The olivine grains studied are essentially free of minor elements (Ti, Al, Cr, Ni, Ca, Na) except for Mn, and fall in the compositional range found by an earlier study. While the compositional ranges of Fe-poor and Fe-rich lamellae overlap, the differences between lamellae richest and poorest in Fe are quite similar, suggestive of their formation by an equilibrium process. Fine-scale microprobing has confirmed earlier compositional data, but has reduced lamella thicknesses to a few micrometers, which is in a good agreement with TEM observations. The structural and compositional data obtained strongly suggest that the lamellar structure in these olivine grains was produced by an exsolution process, which is in qualitative agreement with a recent thermodynamic analysis of phrase relations in the system Mg2SiO4-FeSiO2. Cracks in Fe-rich lamellae could result from expansion during the exsolution process due to the volume difference between Fe-rich and Fe-poor lamellae.
Brearley Adrian J.
Petaev Michael I.
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