A Tofsims Study of Pristine Presolar

Introduction: All presolar graphite grains analyzed to date were extracted from their host meteorite using acid dissolution techniques [1-3]. However, recent studies have suggested that the use of harsh acids may significantly alter the outer surface of presolar SiC grains extracted in this way [4], and similarly may also affect graphite grains. We have previously described a technique for " gently separating " presolar SiC (i.e. without the use of acids) from meteorites [5], and have now adapted this procedure in order to isolate presolar graphite. Separation: Approximately 116mg of CAI-and chondrule-free Murchison matrix material was crushed using a stainless steel mortar and pestle. This was further broken down into grain sizes of <20μm with 138 freeze-thaw cycles while suspending the sample in ultra-pure water. Using a fixed angle rotor centrifuge the grains were first separated into four grain-size fractions. A series of organic, heavy liquids was used to separate each size fraction according to density, selecting for presolar graphite between 1.6-2.26gcm