Hello Lance, Bernd, and list, Nanodiamonds are found not just in carbonacous chondrites and enstatite chondrites, but also in ordinary chondrites of low metamorphic grade. See for example the article "Ubiquitous interstellar diamond and SiC in primitive chondrites - Abundances reflect metamorphism" by Gary R. Huss in Nature, vol. 347, Sept 13, 1990, pp. 159-162. An abstract is available online in the NASA ADS database:
"It is shown here that interstellar diamond and SiC were incorporated into all groups of chondrite meteorites. Abundances rapidly go to zero with increasing metamorphic grade, suggesting that metamorphic destruction is responsible for the apparent absence of these grains in most chondrites. In unmetamorphosed chondrites, abundances normalized to matrix content are similar for different classes. Diamond samples from chondrites of different classes have remarkably similar noble-gas constants and isotropic compositions, although constituent diamonds may have come from many sources. SiC seems to be more diverse, partly because grains are large enough to measure individually, but average characteristics seem to be similar from meteorite to meteorite. These observations suggest that various classes of chondritic meteorites sample the same solar system-wide reservoir of interstellar grains." A more accessible article is "Presolar diamonds in Allende" by Tyrone L. Daulton, in Meteorite!, February 1999, pp. 26-29. For those who can stomach a rather technical treatment of the subject, there is a long (39 pages) two-part paper "Noble gases in presolar diamonds" by Gary R. Huss and Roy S. Lewis in Meteoritics 29 (1994) pp. 791-829. This paper is available online from the NASA ADS database: http://adsabs.harvard.edu/abstract_service.html Enter "presolar diamonds" as Title Words, choose Combine with: AND, and click Send Query. The list of results will include other relevant and more recent articles as well. In their introduction to their 1994 paper, Huss and Lewis say, "Presolar diamonds are relatively abundant in the most primitive members of all chondrite classes." Their study included these meteorites: Orgueil (CI) Semarkona (LL3.0) Bishunpur (LL3.1) Ragland (LL3.5) Mezo Madaras (L3.5) ALHA77214 (L3.5) Tieschitz (H3.6) Dimmitt (H3.8) Qingzhen (EH3) Indarch (EH3-4) Leoville (CV3) Vigarano (CV3) Allende (CV3) Kainsaz (CO3.2) Meteorites mentioned in more recent papers as sources of nanodiamonds include: Axtell (CV3) Roosevelt County 075 (H3.2) Efremovka (CV3) Boriskino (CM) Kaidun (CR/CI polymict breccia) Don't be in a big rush to put your Allende slice under a microscope looking for nanodiamonds. They are VERY tiny, as the "nano-" prefix suggests -- each nanodiamond contains only a few thousand carbon atoms, with diameters ranging from 0.2 to 10 nanometers, and an average of about 2.8 nanometers. This means that one gram of Allende contains about 10 million billion nanodiamonds -- this figure from Tyrone Daulton's article. Best wishes to all, Piper ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
