> They had to have been carbonaceous meteorites of some sort to begin > with, but the articles I've seen don't seem to offer a clear picture > of what they were like before they were shocked. CM, perhaps?
Hello Marc, Fr�d�ric, and List, Here is what I've harvested during the last few minutes: Cyrena Anne Goodrich, Lunar and Planetary Laboratory, University of Arizona Invited Review - Ureilites: A critical review (Meteoritics 27-4, 1992, pp. 327-352): 1) Nilpena contains clasts of carbonaceous chondrite matrix material. Detailed petrographic and mineralogic studies have shown that this material has close affinities to CI - and differs substantially from CM-matrix (Brearley and Prinz, 1989; 1992). Fr�d�ric, "close affinities to CI" would also explain why we do not find any chondrules or relict chondrules in ureilites - there have never been any. But, ... now look at this - it is from the same review by C.A. Goodrich: 2) CI-matrix clasts in Nilpena have an oxygen-isotope composition plotting on the extension of the Allende mixing line on the 17^O-rich side of the terrestrial fractionation line, rather than within the field of CI matrix compositions (Brearley and Prinz, 1992). So the starting material may have been CI- o r CV-like. If it was CV-like, we might really expect to find traces of chondrules or at least chondrule precursor material. Best wishes, Bernd ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://six.pairlist.net/mailman/listinfo/meteorite-list
