Matt Morgan wrote: > I always thought that all ureilites were "primitive".
On the one hand, ureilites are igneous (= evolved) rocks - i.e. they were formed by the solidification of a molten magma and this implies differentiation processes of a planetary-sized asteroidal body. On the other, and this causes scientists a lot of headaches, ureilites display several p r i m i t i v e characteristics. Among these are the following: - high abundances of siderophile elements, - carbon which contains planetary-type noble gases - oxygen isotopic signature of unequilibrated (= primitive / unprocessed) solar system materials A.H.Treiman, J.L.Berkley (1994) Igneous Petrology of the New Ureilites Nova 001 and Nullarbor 010 (Meteoritics 29-6, 1994, 843-848, excerpt): "Ureilites are achondrite meteorites, composed principally of olivine, pyroxenes, and graphite. Ureilites display a bewildering variety of "primitive" and "evolved" characteristics, so that little of their origin is known with certainty." References: CHIKAMI J. et al. (1996) Ureilite formation process with regard to the LEW 88774 ureilite (Meteoritics 31-4, 1996, A027-A028). WANG M.-S. and LIPSCHUTZ M.E. (1994) Constraints on ureilite origin from trace-element contents (Meteoritics 29-4, 1994, 546). Goodrich C.A. (1992) Ureilites: A critical review (Meteoritics 27-4, 1992, 327-352). Best wishes, Bernd ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://six.pairlist.net/mailman/listinfo/meteorite-list
