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Re: Classifying Dar al Gani 140
Jeff Grossman schrieb:
> Bernd and list,
> This is not a typo, but I'm doing my best to eliminate such notation.
> Basically, this is the notation that certain meteoriticists want to
> use to denote breccias. It means that there is a range of petrologic
> types represented amond the various clasts and matrix in the breccia.
> In the case of DaG 140, at least type 3.9 and type 6 material was
> observed. I think that this is POOR nomenclature, and I'm involved
> with trying to find a better way. Here are the reasons that it is
> lousy:
> 1) The hyphen implies a continuous range, and also implies that there
> is no dominant lithology in the breccia. Yet, DaG 140 could be: a) a
> type 3 chondrite with a single equilibrated clast found; b) a type 6
> chondrite with a single type 3 clast found; c) a mixture of types 3,
> 4, 5, and 6 material; a light-dark breccia with mostly comminuted
> matrix and only a few clasts, including type 3 and 6 ones. So, no
> matter what I'm interested in, I have no idea if DaG 140 is
> interesting.
> 2) The classification is likely based on one thin section. If
> somebody else looks at this breccia and they find a type 3.4 clast,
> we would have to reclassify the meteorite. This could happen A LOT
> of times for a single meteorite.
> 3) If the meteorite is like Sharps, a type 3 ordinary chondrite with
> 1% CM2 clasts, how do we name that? H2-3.4? H3.4-CM2? What about
> Kaidun, a breccia of CM, CR, EL, EH and God knows what else...
> CM2-CR2-EL3-6-EH3-4? Ugh.
> 4) Another meteorite might also be a breccia, but a monomict one. It
> might only have type 4 clasts and matrix. It might even be a regolith
> breccia. Yet, it would be classified only as H4.
> So, right now we have a literature polluted with this and other
> nomenclatures (like using a "/" instead of a "-" for the same thing),
> and the community has no way of looking at a catalog and knowing
> what's what. The Meteorite Nomenclature committee has no jurisdiction
> over meteorite classification; it just oversees meteorite names. It's
> just a mess.
> I plan on publishing my recommendations and a statement about this
> problem either in the next Meteoritical Bulletin, or in that same
> issue of MAPS as a refereed paper.
> I'm trying to find a concensus among my colleagues right now. I'll
> post my suggested scheme on the web for public comments this winter
> (I'll tell the list when this happens). Comments are welcome. jeff
Jeff, thank you very, very much for this thoroughly competent, detailed
answer. I am sure that the community would appreciate very much a more
uniform classification system that leaves no doubt as to what we are
dealing with! Looking forward to your ideas!!
Best regards,
Bernd
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