Laboratory Analogues of Microdiamonds Present in Meteorites

Details Laboratory Analogues of Microdiamonds Present in Meteorites Laboratory Analogues of Microdiamonds Present in Meteorites

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27s.210c&link_type=abstract

Meteoritics, vol. 27, no. 3, volume 27, page 210

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The diamonds present in meteorites consist of tiny (average size 26 Angstrom) particles that have been examined in the laboratory (Lewis et al. 1987, 1989). Although various hypotheses about the formation have been formulated, many questions still remain (Anders et al. 1989). Detonation soots contain diamonds that appear similar to the meteoritic samples (Greiner et al. 1988). A systematic analysis of these "analogue" materials can help clarify both the actual nature and the origin of meteoritic diamonds. We analysed three diamond residues extracted by HClO4 oxidation from detonation soots: H1059, H1170, and #27 TNT/RDX (see Greiner et al. 1990 for details about production). Transmission electron microscopy (TEM) has allowed us to determine average sizes of the diamond grains, ~= 40-70 Angstrom, which are in agreement with previous results (Greiner et al. 1988). In addition, dark-field TEM micrographs show a large number of bright irregular spots corresponding to the diamond crystallites. About 1% by mass of each sample was embedded in KBr matrix (200 mg) to perform both Raman and infrared (2.5-20 micrometer) spectroscopy. Raman spectra show a dominant band around 1310 cm^-1, close to the Raman active mode of diamond. It is quite broad due to the small size of the grains. The infrared bands have been compared with those detected both in diamond samples, isolated from Murchison C2 and Allende C3V chondrites (Lewis et al. 1989), and in the organic residues of the Orgueil (Wdowiak et al. 1988) and the Murchison meteorites (Cronin and Pizzarello 1990). The bands can be attributed to functional groups present on the surface of the grains. The bands of #27 TNT/RDX and H1170 samples match in position the features of meteoritic diamonds at 2.94, 3.17, 3.42, 3.51, 4.27, 5.64, 6.10, 6.86, 7.13, 8.10, 8.53, and 9.02 micrometers, while most of them are lacking in the spectrum of H1059. Therefore, we tend to exclude the extraction method as the main cause of their presence. On the other hand, we note that most of the bands are observed also in organic residues. Only some features appear typical of diamond samples. An intense peak at 5.64 micrometers for meteoritic diamonds is attributed to C=O vibration in -COOH and, perhaps, also in -CHO (Lewis et al. 1989). Sample #27 TNT/RDX has a similar peak, while H1170 diamond and the meteoritic organic residues show a peak shifted to 5.8-5.9 micrometers. A broad band around 8.5 micrometers is present in all the diamond samples and it may be due to N in diamond and/or to a C-O stretching resonance (Lewis et al. 1989). A similar feature is shifted to 8.1 micrometers in organic compounds. In conclusion, only some of the diamond samples extracted from detonation soots well reproduce the crystallographic, size, and optical properties of extraterrestrial microdiamonds. Therefore, it appears of great interest to relate systematically the characteristics of the laboratory products to their formation conditions. This analysis will provide useful hints also about the actual origin and formation mechanisms of diamonds present in meteorites. Acknowledgments: J.R. Stephens acknowledges support from a NATO Collaborative Research Fellowship. This work was partly supported by ASI, CNR, and MURST 40% and 60 %. References: Anders, E., Lewis R.S., Ming T., and Zinner E. (1989) In Interstellar dust (eds. L.J. Allamandola and A.G.G.M. Tielens), pp.389-402. Kluwer Acad. Publ., Dordrecht. Cronin J.R. and Pizzarello S. (1990) Geochim. Cosmochim. Acta 54, 2859-2868. Greiner, N.R., Phillips, D.S., Johnson J.D., and Volk F. (1988) Nature 333, 440-442. Greiner, N.R., Rogers Y.C., and Spall W.D. (1990) Los Alamos National Laboratory document LA-11837-MS. Lewis, R.S., Bright D., and Steel E. (1987) Meteoritics 22, 445. Lewis, R.S., Ming T., Wacker J.F., Anders E., and Steel E. (1987) Nature 326, 160-162. Wdowiak, T.J., Flickinger G.C., and Cronin J.R. (1988) Astrophys. J. 328, L75-L79.

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