WG: [meteorite-list] Classification question

From: Nicholas Gessler <gessler_at_meteoritecentral.com>
Date: Wed May 12 20:30:13 2004
Message-ID: <6.0.0.22.2.20040512172832.03fc3b48_at_mail.ucla.edu>

While we're at it, what's the difference between a "3" and a "3.0?"
Does a "3" imply that no one made any finer discrimination?
Or does a "3" imply that it's really a "3.0?"
Cheers,
Nick

At 08:23 AM 4/14/2004, J?rn Koblitz wrote:
>Dear Pierre,
>
> > I've got a (stupid ?) question about the classification of
> > the chondrites.
> >
> > What is the difference between this kind of classification :
> > For example L3.6, L3-6 or H5/6
> >
> > Is the sign "-" the same as "/" or "." in this case ?
>
>Regarding the use of hyphens and slashes, see the postings to the list of
>March 19 to 23 (pasted below).
>
>The use of "." in the classification (e.g. L3.6) is used in case that a
>petrologic SUBtype has been obtained, either by measuring the induced
>thermoluminescence (TL) or by calculation of the percentage mean deviation
>(PMD) of the fayalite and ferrosilite contents of olivine and pyroxene,
>respectively, measured by microprobe (EPMA). The subtype is just a finer
>subdivision and is only used for unequilibrated (i.e. type 3) chondrites.
>It is a scale for the amount of thermal metamorphism a chondrite has
>experiences since its accretion. In this respect, a 3.0 indicate the least
>metamorphosed (or most primitive / less heated) type 3 chondrite. On the
>other hand, a type 3.9 chondrite is almost chemically equilibrated like
>type 4 and higher, as it has experienced considerable heating (e.g. by
>impact shock) during its lifetime on the parent-body (planetesimal or
>asteroid).
>
>Hope this answers your question.
>
>Best regards,
>
>Joern
>
>_______________________________________________________________________________
>Joern Koblitz
>MetBase Editor
>The MetBase Library of Meteoritics and Planetary Sciences
>Benquestrasse 27
>D-28209 Bremen, Germany
>phone: +49 421 24 100 24
>fax: +49 421 24 100 99
>email: info_at_metbase.de
>_______________________________________________________________________________
>
>
>
>
>
>
>
>
>Hello John, David and Bernd,
>
>Sorry for my late reply - I'm not online on weekends.
>
>You are right, it's a messy situation with the use of slashes "/" and
>hyphens "-" and as Jeff outlined long time ago, it actually depends on the
>research group who does the classification. With MetBase, I stick to the
>presently preferred rules that "/" indicates a transitional type and "-" a
>breccia. However, as complicated as it could be, imagine that a
>transitional group like H/L contains clasts of different petrologic types,
>e.g. 4 and 6: should it then be designated H/L4-6 or (H/L)4-6 or H4-6/L4-6?
>Regarding the transitional petrologic type designations, e.g. H5/6: beware
>that there is always a personal bias by the person who did the
>classifications: one researcher will classify an H chondrite H5, another
>researcher the same chondrite H6 and a third person would give it H5/6:
>there is always an uncertainty of +/- 0.5 for equilibrated ordinary
>chondrites. That's why some researchers think that it is always
>appropriate to assign straight numbers and to prevent transitional
>numbers, which is rather a sign of shakiness. Regarding the use of
>parentheses, e.g. "LL/(L)3" or "LL(L)3": this problem is rather restricted
>to very unequilibrated chondrites as Jeff pointed out. Since highly
>unequilibrated chondrites show large variations in mineral chemistry (e.g.
>wide ranges of olivine, pyroxene or metal compositions), one has to do a
>large number of microprobe and (oxygen) isotopic measurements to gain
>certainty on the classification. This is very time-consuming and
>expensive. Further, many hot-desert finds are higly weathered which makes
>it difficult to classify them based on chemical compositions (terrestrial
>contamination).
>
>David: Regarding the differences in designations beween Met. Bulletin and
>MetBase, I have to check the literature sources of the MetBase information
>and let you know lateron if I can clearify.
>
>Joern
>
> > -----Urspr?ngliche Nachricht-----
> > Von: j.divelbiss_at_att.net [mailto:j.divelbiss@att.net]
> > Gesendet: Freitag, 19. M?rz 2004 22:27
> > An: bernd.pauli_at_paulinet.de
> > Cc: dgweir_at_earthlink.net; J?rn Koblitz;
> > meteorite-list_at_meteoritecentral.com
> > Betreff: Re: [meteorite-list] Hyphens / Slashes
> >
> >
> > Bernd. Dave, Joern and others,
> >
> > Bernd, thanx for the previously submitted info from Jeff on
> > slashes and dashes.
> >
> > That should certainly clear it up the confusion, right Dave. :)
> >
> > John
> >
> > BTW: Joern...in all seriousness I really appreciate you
> > responding to this thread.
> >
> >
> > > > For chondrite groups, petrologic types, shock stages, and
> > weathering
> > > > grades, slashes (e.g., H5/6) indicate transitional
> > assignments. Hyphens
> > > > in petrologic type assignments for chondrites (e.g.,
> > H5-6) indicate the
> > > > range of types observed in breccias. Group names such as
> > "L(LL)" indicate
> > > > uncertain assignments, with the less probable group in
> > parentheses.
> > >
> > > Hello All,
> > >
> > > I was waiting for Jeff Grossman to chime in here, because
> > > on Monday, 07 Sep 1998, Jeff wrote to this to the List (excerpts):
> > >
> > > 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.
> > >
> > > There is NO convention for naming brecciated chondrites.
> > Many, including the
> > > group at Muenster, like to use a slash to separate
> > components of a breccia.
> > > However, nobody has ever written a paper on the subject,
> > and the rules are up
> > > for grabs. I happen to be of the opinion that the slash is
> > ridiculous for many
> > > reasons,
> > > including the one brought up here: we will always need to
> > be reclassifying
> > > breccias
> > > whenever somebody finds a new lithology among the clasts.
> > This is not feasible.
> > >
> > > These parentheses are used by some researchers when they
> > cannot determine with
> > > certainty the group assignment of a meteorite. L(LL)3 means
> > that they lean
> > > towards
> > > L3, but it could be an LL3. Indeed, it is very difficult to
> > differentiate
> > > between L3 and LL3
> > > chondrites, as they may have similar sized chondrules,
> > similar metallography,
> > > similar
> > > silicate compositions (i.e., highly heterogeneous), and
> > even oxygen isotope
> > > compositions
> > > and trace elements cannot always resolve them well. Even
> > some of the most
> > > famous, best
> > > studied meteorites have been given various classifications
> > in different parts of
> > > the literature
> > > (e.g., Tieschitz, Krymka, Bishunpur).
> > >
> > > If any meteorite has been called "LL/(L)3", I have no clue
> > what this means.
> > >
> > >
> > > To: dgweir_at_earthlink.net
> > > koblitz_at_microfab.de
> > > Cc: meteorite-list_at_meteoritecentral.com
> > >
> > >
> > > ______________________________________________
> > > Meteorite-list mailing list
> > > Meteorite-list_at_meteoritecentral.com
> > > http://www.pairlist.net/mailman/listinfo/meteorite-list
> >
>
> > -----Urspr?ngliche Nachricht-----
> > Von: Pierre-Marie PELE [mailto:pierre.pele_at_voila.fr]
> > Gesendet: Mittwoch, 14. April 2004 08:15
> > An: meteorite-list_at_meteoritecentral.com
> > Betreff: [meteorite-list] Classification question
> >
> >
> > Hello to the List !
> >
> > I've got a (stupid ?) question about the classification of
> > the chondrites.
> >
> > What is the difference between this kind of classification :
> > For example L3.6, L3-6 or H5/6
> >
> > Is the sign "-" the same as "/" or "." in this case ?
> >
> > Thanks a lot,
> >
> > Pierre
> > ------------------------------------------
> >
> > Faites un voeu et puis Voila ! www.voila.fr
> >
> >
> >
> > ______________________________________________
> > Meteorite-list mailing list
> > Meteorite-list_at_meteoritecentral.com
> > http://www.pairlist.net/mailman/listinfo/meteorite-list
> >
>
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Received on Wed 12 May 2004 08:30:07 PM PDT