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Extreme Si-29 and Si-30 enrichments found in
rare Murchison SiC-containing graphites.
Croat K. and Stadermann F. J. (2008)
Lunar & Planet. Sci. 39, Abstract #1739.
ABSTRACT
Although rare (in <1% of graphites), silicon carbides
are found as internal grains within Murchison KFC1 onion
graphites, with four instances reported thus far. These
composite grains (e.g. SiCs found within graphite) are of
particular interest, as they are a clear case in which both
presolar phases form from the same star. Here we report on
the microstructure as well as the chemical and isotopic
compositions of two newly-discovered graphites containing
relatively large internal SiCs (100-225 nm in size).
NanoSIMS isotopic analyses of both SiC-containing graphites
reveal large 29Si and 30Si enrichments
indicative of a massive star origin, with one nearly as
extreme as the unusual SiC previously found. Until now, an
anomaly of this type had been measured only once among tens
of thousands of presolar SiCs.
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