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Fisenko, A.V.; Verchovsky, A.V.; Semenova, L.F. and Pillinger, C.T.
(2002).
Abstract
Amounts and isotopic compositions of C, N, and noble gases were measured in the same gas portions extracted by step heating (over the temperature interval of 300–2000°C) of two different-size fractions of interstellar diamond from the Efremovka CV3 chondrite. The analysis of these data and their comparison with the data obtained for the same fractions during their oxidation and with results of the pyrolysis of whole-rock diamond samples from other chondrites led us to conclude that (1) the fine-grained diamond is more heat-resistant than the coarse-grained diamond, perhaps, because of an increase in the percentage of defect grains and the concentrations of defects in them with an increase in the grain size; (2) graphitization and oxidation of nanometer-sized diamond grains result in an uniform (for example, layer by layer) mechanism of destruction; (3) N, He, and, to a lesser degree, Ne release during pyrolysis proceeds predominantly by means of diffusion, whereas Ar and Xe are liberated mostly during grain destruction; (4) coarse-grained diamond is enriched in associations of two and more N atoms, which can be released at lower temperatures than those of single N atoms; and (5) an increase in the thermal-metamorphism grade of the parental material of chondrites leads to a more rapid destruction of coarse-grained diamond than its fine-grained analogue. For example, the material of the Indarch chondrite, which was affected by the most intense thermal metamorphism among all chondrites considered,
contains mainly fine-grained interstellar diamond.
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