Carbynes Allende

Another recent interesting finding is that previously unknown organic polymers or "amorphous carbon," which are noble gas carriers in meteorites, are actually carbynes. Five different carbynes have been identified in the Murchison and Allende carbonaceous... 

Smith, P. P. K. Buseck, P. R. 1981a Carbon in the Allende meteorite evidence for poorly graphitised carbon rather than carbyne. Proc. Lunar. Sci. Conf. 12b, 1167-1175. 

Most of the carbon in the Allende C3V chondrite is present in elemental form, rather than as polymer or extractable organic compounds (Breger et al., 1972). It was originally called amorphous carbon , since it is amorphous to x-rays. However, recent work shows it to be carbyne (Whittaker et al., 1980 Hayatsu et al., 1980b) a triply bonded, linear allotrope of elemental carbon. Carbyne exists in at least 10 varieties, ranging between graphite and diamond in hardness and density (Whittaker, 1978 and references therein). 

At least 4 carbynes — carbon VI ( ), VIII, X, and XI — have been identified in Allende on the basis on x-ray diffraction (Whittaker et al., 1980). Ion microprobe data (specifically, the predominance of even-numbered carbon fragments) suggests that at least 80% of the acid-insoluble carbon fraction is carbyne. Some of the carbynes are thermally labile, and at 250-330 °C give off various fragments, in-clpding 2 ( = 1-5) and (CsC) CN (n = 1-3). Smaller amounts of carbynes have been found in the Murchison C2 chondrite (Whittaker et al., 1980), where they are masked by the abundant organic polymer (Hayatsu et al., 1977). 

Chemical state of carbon in carbonaceous chondrites agrees with that predicted from their formation conditions (indicated by boxes), as inferred from isotopic fractionation of O and C, or abundanc es of volatile metals (Table 1 and Fig. 11 Onuma et al., 1972, 1974 Anders et al., 1976). Cl and C2 chondrites, having formed between 360 and 400 K, contain mainly organic compounds with only traces of carbynes (Whittaker et al., 1980). C3 chondrites contain mainly elemental carbon, which, at least in the case of Allende, is present as carbynes rather than graphite... 

Murchison and Allende meteorites contained a substantial number of individual crystalline carbyne grains [21] was almost certainly incorrect. In yet another ultrathin section and acid-resistant residue of the Murchison meteorite C=C functional groups were identified but they were linked to aromatic carbons [61]. The only reliable evidence for carbyne (i.e. chaoite) in meteorites [20] suggests it formed in situ by solid-state carbon annealing that is an acceptable geological process. A tenet of cosmochemistry is that all solids initially formed by condensation from a cooling vapor phase. Whether condensation proceeded at (near) thermodynamic equilibrium, kinetically controlled, metastable equilibrium, or a combination, remains open to debate. Kinetically controlled, metastable condensation is likely for silicates [6,79] and was proposed for carbyne condensation from interstellar polycyanoacetylenes [80]. 

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