AW: [meteorite-list] Anomalous and Ungrouped Ordinary Chondrites

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:32 2004
Message-ID: <5.1.0.14.2.20031019193221.01b903f8_at_gsvaresm02.er.usgs.gov>

Norbert stated the facts well about ungrouped and anomalous chondrites.

There are no rules or guidelines for grouping meteorites. However, a lot
of researchers subscribe to the idea, which I think originated with John
Wasson, that it takes 5 to sufficiently define the properties of a bunch of
related meteorites that a name could be proposed. The Editors of the
Meteoritical Bulletin and the Catalogue of Meteorites probably wouldn't
endorse a group-name if there were less than 5. Of course, there are
researchers who really want to be the ones to coin new names, and they
sometimes get a bit hasty. Anyway, for smaller sets of meteorites, the
term "grouplet" is preferred by many, as is the suffix "-like", each
modifying the name of the best-known member.

jeff

At 11:19 PM 10/19/2003 +0000, j.divelbiss_at_att.net wrote:
>Norbert,
>
>I didn't read your comment very closely. It looks like you are saying it
>takes 5 samples to make a group. Where does that criteria come from? I know
>you are involved with the Society...so maybe there are known guidelines after
>all. thanx in advance.
>
>John
>
> > Hi John, and list,
> >
> > As to the ungrouped HaH 180, and Deakin 001, it has been suggested
> > that both represent samples of a new and previously unsampled parent
> > body. If that holds to be true, they will never get a LL or L
> > classification. Ungrouped just means that a sample can't be
> > assigned to any of the established groups, and that means also
> > that they do most probably represent a unique parent body. Now,
> > if we find three more meteorites like HaH 180, or Deakin 001,
> > scientists will most likely create a new group, and then these
> > samples won't be ungrouped, any longer.
> >
> > The term "anomalous" is used for meteorites that actually can be
> > assigned to an existing group, but that differ in some aspects from
> > the other known members of that group. Thus, HaH 180 isn't anomalous,
> > it's simply ungrouped.
> >
> > Short: an ungrouped chondrite most probably stems from an asteroid
> > that hasn't been sampled so far. An anomalous LL, for example, is
> > most probably from the LL parent body/asteroid, but it differs from
>
> > the other LL members in some respect. The petrologic grades have
> > nothing to do with that, and of course an ungrouped chondrite can
> > be a 3.5, or a plain 6.
> >
> > Hope this helps ;-)
> >
> > Best,
> > Norbert
> >
> > A puzzled John wrote:
> >
> > > Hello all,
> > >
> > > I've always been intrigued but puzzled about the classification of a few
> > > ordinary chondrites into the black hole of assigned classification
> > > names...ungrouped and/or anomalous. Some are specified with petrologic
> > > assignments and others without. Ebay on occasion offers us Hah
> > > 180 that is classified as an anomalous 3.5 ordinary chondrite and
> > > Dhofar 535 that is classified as ungrouped, and without a petrologic
> > > designation in its' description. According to David's site below...Hah
> > > 180 is similar to Deakin 001. And there maybe others I am not thinking
> > > of. Oxygen isotopes and weathering seem to be some of the key factors...
> > > and as stated on David's site they may come from a proximity close to
> > > where enstatite chondrites were formed, and in my opinion their
> appearance
> > > makes them at least look like some of the EL3's out there.
> > >
> > > Does anyone know what the latest theory is for these and will
> > > they one day
> > > get an official LL3 to 3.5 anomalous label which would finally
> > > give them a
> > > home? Seems to me to call them anything else puts them/keeps them in
> > > classification limbo.
> >
>
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Dr. Jeffrey N. Grossman phone: (703) 648-6184
US Geological Survey fax: (703) 648-6383
954 National Center
Reston, VA 20192, USA
Received on Sun 19 Oct 2003 07:48:18 PM PDT