WG: [meteorite-list] Classification question

From: Jörn Koblitz <koblitz_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:14 2004
Message-ID: <E5E6112EA31FA24CB448E091C6883C0517A01B_at_server2000.microfab.de>

Dear Pierre,

> I've got a (stupid ?) question about the classification of=20
> the chondrites.
>=20
> What is the difference between this kind of classification :=20
> For example L3.6, L3-6 or H5/6
>=20
> 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?=20
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=FCngliche Nachricht-----
> Von: j.divelbiss_at_att.net [mailto:j.divelbiss@att.net]
> Gesendet: Freitag, 19. M=E4rz 2004 22:27
> An: bernd.pauli_at_paulinet.de
> Cc: dgweir_at_earthlink.net; J=F6rn Koblitz;
> meteorite-list_at_meteoritecentral.com
> Betreff: Re: [meteorite-list] Hyphens / Slashes
>=20
>=20
> Bernd. Dave, Joern and others,
>=20
> Bernd, thanx for the previously submitted info from Jeff on=20
> slashes and dashes.
>=20
> That should certainly clear it up the confusion, right Dave. :)
>=20
> John
>=20
> BTW: Joern...in all seriousness I really appreciate you=20
> responding to this thread.=20
>=20
>=20
> > > For chondrite groups, petrologic types, shock stages, and=20
> weathering
> > > grades, slashes (e.g., H5/6) indicate transitional=20
> assignments. Hyphens
> > > in petrologic type assignments for chondrites (e.g.,=20
> H5-6) indicate the
> > > range of types observed in breccias. Group names such as=20
> "L(LL)" indicate
> > > uncertain assignments, with the less probable group in=20
> parentheses.
> >=20
> > Hello All,
> >=20
> > I was waiting for Jeff Grossman to chime in here, because
> > on Monday, 07 Sep 1998, Jeff wrote to this to the List (excerpts):
> >=20
> > Right now we have a literature polluted with this and other=20
> nomenclatures
> > (like using a "/" instead of a "-" for the same thing), and=20
> the community has
> > no way of looking at a catalog and knowing what's what. The=20
> Meteorite
> > Nomenclature committee has no jurisdiction over meteorite=20
> classification;
> > it just oversees meteorite names. It's just a mess.
> >=20
> > There is NO convention for naming brecciated chondrites.=20
> Many, including the
> > group at Muenster, like to use a slash to separate=20
> components of a breccia.
> > However, nobody has ever written a paper on the subject,=20
> and the rules are up
> > for grabs. I happen to be of the opinion that the slash is=20
> ridiculous for many=20
> > reasons,
> > including the one brought up here: we will always need to=20
> be reclassifying=20
> > breccias
> > whenever somebody finds a new lithology among the clasts.=20
> This is not feasible.
> >=20
> > These parentheses are used by some researchers when they=20
> cannot determine with
> > certainty the group assignment of a meteorite. L(LL)3 means=20
> that they lean=20
> > towards
> > L3, but it could be an LL3. Indeed, it is very difficult to=20
> differentiate=20
> > between L3 and LL3
> > chondrites, as they may have similar sized chondrules,=20
> similar metallography,=20
> > similar
> > silicate compositions (i.e., highly heterogeneous), and=20
> even oxygen isotope=20
> > compositions
> > and trace elements cannot always resolve them well. Even=20
> some of the most=20
> > famous, best
> > studied meteorites have been given various classifications=20
> in different parts of=20
> > the literature
> > (e.g., Tieschitz, Krymka, Bishunpur).
> >=20
> > If any meteorite has been called "LL/(L)3", I have no clue=20
> what this means.=20
> >=20
> >=20
> > To: dgweir_at_earthlink.net
> > koblitz_at_microfab.de
> > Cc: meteorite-list_at_meteoritecentral.com
> >=20
> >=20
> > ______________________________________________
> > Meteorite-list mailing list
> > Meteorite-list_at_meteoritecentral.com
> > http://www.pairlist.net/mailman/listinfo/meteorite-list
>=20

> -----Urspr=FCngliche 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
>=20
>=20
> Hello to the List !
>=20
> I've got a (stupid ?) question about the classification of=20
> the chondrites.
>=20
> What is the difference between this kind of classification :=20
> For example L3.6, L3-6 or H5/6
>=20
> Is the sign "-" the same as "/" or "." in this case ?
>=20
> Thanks a lot,
>=20
> Pierre
> ------------------------------------------
>=20
> Faites un voeu et puis Voila ! www.voila.fr=20
>=20
>=20
>=20
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
> http://www.pairlist.net/mailman/listinfo/meteorite-list
>=20
Received on Wed 14 Apr 2004 11:23:45 AM PDT