Graphite Whiskers Discovered in Cv 3 Meteorites .

Introduction: We report the serendipitous discovery of a small number of graphite whiskers (GWs), a rare polymorph of carbon, in a range of settings within several CV3 meteorites [1]. Currently accepted growth conditions for GWs indicate that this unusual phase requires that the parent mineralogy experienced high temperature processing in contact with a carbon-containing gas. Description of Graphite Whiskers: Morphology. GWs are essentially rolled spindles of graphite, somewhat tapered towards one end and typically microns in length (Figure 1). They are distinct from carbon nanotubes, which are seamless tubes of graphite, and from carbon fibers, which typically consist of soild, mixed turbostratic and graphitic carbon. GW Synthesis. The formation conditions of GW are not adequately characterized, but the laboratory synthesis methods available in literature involve temperatures ranging up to 2273 K in flowing gas [2] and ~3900 K in an arc discharge [3]. One study shows that, on the basis of thermodynamics calculations, growth of graphite whiskers is preferred over planar graphite at high temperatures [4]. GWs have been described in only three terrestrial settings, all of which contained graphite deposited or altered at high temperatures [5-7]. One study of GW synthesized from charcoal found a range of morphologies including shorter, conical GW, spindle-shaped whiskers, and other variations [8]. These shapes are arguably the result of heteroatom contaminants arising from a natural carbon sample as opposed to the high-purity gases used to produce GW in other laboratory experiments. It is reasonable to expect that such a range of shapes can be expected in meteoritic and other natural settings. While further work is required to properly refine GW formation conditions , the bulk of available information implies that the presence of GW implies that the parent mineralogy experienced high temperature exposure to a carbon-containing vapor. Alternatively, GW may pre-date their parent mineral assemblages. It is worth noting that both the high temperature necessary for GW synthesis and their rarity in natural settings make them an unlikely laboratory contaminant. Raman Spectra. Investigation by Tan et al showed that GWs feature unique Raman spectral features that simplify their identification, namely a second-order carbon D (disorder) band (or D*) around 2680 cm