The iron meteorite cooling rates generally range from about 1 - 100ºC/Myr. The reason for such slow rates is that the metal cores are buried deeply within silicate mantles and heat cannot readily escape. The coarseness of the Widmanstatten pattern is a function of cooling rate -- more slowly cooled irons will develop thicker kamacite lamellae. But there are two other factors that govern the coarseness of the structure -- the Ni concentration and the nucleation temperature. The lower the Ni concentration in the metal, the more kamacite will develop upon cooling. Metal that begins to nucleate at a higher temperature will have a longer period within which kamacite can grow.
Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
