[meteorite-list] LL6/7 classification answers

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:55 2004
Message-ID: <>

I don't think I explained the point I was trying to make very
well. Because all of the properties used to distinguish the petrologic
types are continuous, the Van Schmus and Wood scheme isn't really meant to
have transitional types. There aren't gaps between the types as there are
between, say, the olivine compositions of H and L, or L and LL
chondrites. In the latter case, when a meteorite like Bjurboele comes
along with a truly intermediate composition, one can classify it as L/LL to
point up its difference from members of the two groups. However with
petrologic types, most workers try to assign chondrites to one of the
grades or another. If one property seems more like type 6 and other
properties seem more like type 5, most researchers would choose the one
that seems best --type 5-- and not worry too much about it. Now there are
some people who would resolve such conflicts by using a slash, but most of
us wound not. Both ways are OK; it's a matter of taste. But more
classifiers would decide one way or the other rather than sit on the fence.

At 11:48 AM 3/27/2004 -0500, David Weir wrote:
>Hello list,
>I'm staying out of the fray here, but since I shared my thoughts on
>Mike's new meteorite classification (NWA 2092), and since we heard from
>Jeff Grossman on the possible ambiguity of the exact meaning of this
>classification, and since Mike wasn't able to share the classification
>details, I felt compelled to investigate this classification with the
>source, Dr. Ted Bunch, and report back here.
>He told me that the LL6/7 was meant to imply a transition from 6 to 7,
>and shared with me his reasons, which are consistent with a transitional
>metamorphic stage between 6 and 7, despite any mutual exclusivity that
>Dodd's rules may imply. Ted's use of a slash between the 6 and 7 is
>consistent with the recommendations of NomCom, and is not used to imply
>an "I'm not sure" scenario, which Jeff indicated is sometimes done. I'll
>let the write-up speak for itself, which Ted says will likely be a full
>separate entry in the Bulletin.
>Meteorite-list mailing list

Dr. Jeffrey N. Grossman
Chair, Meteorite Nomenclature Committee (Meteoritical Society)
US Geological Survey
954 National Center
Reston, VA 20192, USA
Phone: (703) 648-6184 fax: (703) 648-6383
Received on Sat 27 Mar 2004 01:25:38 PM PST

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