[meteorite-list] Re: Rubble pile asteroids
From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:32 2004 Message-ID: <20020926175454.52797.qmail_at_web80304.mail.yahoo.com> --- Herbert Raab <herbert.raab_at_utanet.at> wrote: > > I still think that there might be fuzzy borders > between > metamorphic grades, or that a small thin section is > not representative for the whole specimen. > Once again, Herbert has hit the nail square on the head. It is a lot to ask of a single thin section to speak for an entire meteoroid, let alone parent body. But with a strewn field you have the opportunity to sample multiple specimens, and with each additional thinsection you add to your confidence level for class (and metamorphic grade). I have never seen a table of Gold Basin specimens that have been classified, so I can only speak for the 22 stones that I have had analyzed, and the consensus among researchers is that there was, indeed, an L6 meteorite fall in the Gold Basin Area. How to reconcile that fall and the Gold Basin (L4) fall, hasn't been decided, yet. Herbert continues: > I just want to caution that there might be > UNCERTAINTIES in the assignement of metamorphic > grades, but I am no scientist, so I don't really > know. > Just my three (Euro) Cents worth of thoughts... Well, in defense of all the petrologists that determine the classifications of our meteorites, you can rest assured that they have no uncertainty when they assign a metamorphic grade. When researchers examine the petrologic fabric of a stony in thin section, and those petrologists find orthopyroxenes, or they find feldspars, there is no uncertainty in that observation, and hence there is no uncertainty in which metamorphic grade they must assign. Of course, if the sample is extremely small, or the classifier "spends too little time examining a thin section, this could pose problems, but I wouldn't call it "uncertainty". ("Uncertainty in assignment" is probably just an unfortunate choice of words. I prefer to use the term "differing institution-criteria", but I'd rather not "go there" at this time;-) Bob V. __________________________________________________ Do you Yahoo!? New DSL Internet Access from SBC & Yahoo! http://sbc.yahoo.com Received on Thu 26 Sep 2002 01:54:54 PM PDT |
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