Mathematics – Logic
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.136..677g&link_type=abstract
Earth and Planetary Science Letters, vol. 136, Issue 3-4, pp.677-692
Mathematics
Logic
4
Scientific paper
An attempt has been made to isolate the carriers of isotopically `heavy' ( 15 N-enriched) nitrogen in the unusual chondrite Acfer 182, by preparing an oxidised HF/HCl-resistant residue. Analysis of the residue showed that, along with much of the carbon, almost all of the isotopically heavy nitrogen was removed by the acid treatment, suggesting that this component is associated with carbonaceous material. Several new nitrogen-bearing components were revealed. Most of the nitrogen left in the sample (which has a total 15 N ca. -110 ) is enriched in 14 N, and contained in clumps of nanodiamonds, similar in appearance, grain size, 13 C, 15 N and C/N ratio to the interstellar nanodiamonds found in primitive carbonaceous, ordinary and enstatite chondrites. The abundance of nanodiamonds in Acfer 182 (10-15 ppm) can best be explained if they are carried by the clasts of CM-like matrix material present in the whole-rock sample. The remainder of the carbon and nitrogen in the residue was present as three further populations of morphologically distinct diamonds, with different isotopic compositions and C/N ratios, implying different (solar system) formation origins. In addition to diamonds, carbon occurs as a hexagonal polymorph of SiC. Unfortunately, mixing of carbon combusting from diamond with that from SiC precluded determination of a true 13 C for the SiC, but it is conceivable that, like interstellar nanodiamonds, SiC is presolar and occurs in the matrix clasts. Acfer 182 might also contain silicon nitride (Si 3 N 4 ; nierite), although none was identified by TEM.
Arden John W.
Grady Monica M.
Lee Martin R.
Pillinger Colin T.
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