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Structural and isotopic microanalysis of presolar SiC from supernovae
Author(s) -
Mairin HYNES K.,
Kevin CROAT T.,
AMARI Sachiko,
MERTZ Aaron F.,
BERNATOWICZ Thomas J.
Publication year - 2010
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2010.01045.x
Subject(s) - murchison meteorite , presolar grains , microanalysis , meteorite , crystallography , microstructure , materials science , diffraction , grain size , supernova , analytical chemistry (journal) , chondrite , mineralogy , chemistry , metallurgy , physics , astrophysics , astrobiology , optics , organic chemistry , chromatography
– We report on the microstructure, crystallography, chemistry, and isotopic compositions of seven SiC X grains and two mainstream grains from the Murchison meteorite. TEM crystallographic analysis revealed that the X grains (approximately 3 μm) are composed of many small crystals (24–457 nm), while the similarly sized mainstream grains are composed of only a few crystals (0.5–1.7 μm). The difference in crystal size likely results from differences in their formation environments: the X grain crystals evidently formed under conditions of greater supersaturation and rapid growth compared to their mainstream counterparts. However, the same polytypes are observed in both mainstream and X grains. Six X grains and both mainstream grains are entirely the 3C‐SiC polytype and one X grain is an intergrowth of the 3C‐SiC and 2H‐SiC polytypes. EDXS measurements indicate relatively high Mg content in the X grains (≲5 atomic%), while Mg was undetectable in the mainstream grains. The high Mg content is probably from the decay of 26 Al into 26 Mg. Estimates of the 26 Al/ 27 Al ratios, which range from 0.44–0.67, were made from elemental Mg/Al ratios. This range is consistent with the 26 Al/ 27 Al ratios inferred from previous isotopic measurements of X grains. We also report the first direct observations of subgrains in X grains, including the first silicides [(Fe,Ni) n Si m ]. Diffraction data do not match any previously observed presolar phases, but are a good fit to silicides, which are predicted stable SN condensates. Eight subgrains with highly variable Ni/Fe ratios (0.12–1.60) were observed in two X grains.