[meteorite-list] Ordinary chondrites - rarest to the most common classes

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Wed, 16 Dec 2009 10:26:00 -0500
Message-ID: <OFD810B48C.266EF23D-ON0525768E.0054D395_at_usgs.gov>

At 09:27 AM 12/16/2009, Chladnis Heirs wrote:
>Indeed,
>
>it's for the first time, that I read that R-chondrites are included in the
>OC-group. If so, why exactly them and not the K-chondrites, the Carbonaceous
>from grade 3-6, the ungrouped and the enstatite chondrites too?

I didn't say they ARE included in the OCs... I
said that I thought they should be. As far as I
know, I am alone in this opinion. There are only
two Kakangari-like chondrites, and I am not
prepared to put them anywhere. I'm not sure what
the rest of the question means, but many
ungrouped chondrites can be and are associated
with a major class, as in "ungrouped carbonaceous chondrite".

jeff


>
> >valuable type of OC from a
> >scientific perspective is petrologic type 3.00-3.01
>
>Where one has to say, that it's maybe too early to say that,
>Because the classification with decimal places, (even with two!), is a
>relatively new occurrence - most classifiers seems still to prefer to use a
>simple "3" - so that in case, there are still a lot known type-3ers awaiting
>to be revisited regarding the degree of their (un)equilibration.
>
>But I agree - "Ordinary" is a somewhat misleading term,
>- as the ordinary chondrites have told us most about the origin and
>formation of the solar system, the planets and ourselves, more than any iron
>or any lunar rock!
>
>Keep that always in mind, if you are tempted, now in the end of the
>desert-era and the decreed end of meteorite finding in so many countries,
>with all their weird and fancy exotic types, to wrinkle your nose about the
>"ugly" ordinary 25$-a-kilo-chunk from NWA-wonderland!
>Rare as brilliants they are - and they were our beginnings!
>
>Happy holidays to all!
>Martin
>
>
>-----Urspr?ngliche Nachricht-----
>Von: meteorite-list-bounces at meteoritecentral.com
>[mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von Jeff
>Grossman
>Gesendet: Mittwoch, 16. Dezember 2009 11:33
>An: Meteorite-list
>Betreff: Re: [meteorite-list] Ordinary chondrites - rarest to the most
>common classes
>
>I agree with Doug... the rarest and most valuable type of OC from a
>scientific perspective is petrologic type 3.00-3.01, from any of the
>chemical groups. Only one is known... Semarkona. If we take a more
>expansive definition of "ordinary chondrite" than most of my rather
>conservative colleagues are normally willing to accept, I would say that
>the rarest group of OCs is the R chondrites (only ~100 are known and
>many of those are paired). In addition, a number of unique ungrouped
>meteorites are OC-like. But again, I don't know of any colleagues who
>agree with me that R chondrites are in the OC class. [I would say that
>the OC class has two clans, the H-L-LL clan and the R clan].
>
>Jeff
>
>Mexicodoug wrote:
> > Hi Melanie and thanks for the enthusiasm you add to the list ...
> >
> > Here's a high to low sorting of the "ordinary chondrites", for over
> > 32,000 meteorites:
> >
> > 22.0% L6 ("most common")
> > 19.9% H5
> > 12.9% L5
> > 12.3% H4
> > 11.5% H6
> > 7.8% LL5
> > 4.2% LL6
> > 3.3% L4
> > 2.2% H3
> > 2.0% L3
> > 0.8% LL4
> > 0.8% LL3
> > 0.1% L7
> > 0.1% LL7
> > 0.03% H7 ("least common")
> >
> > But this "common" and "rare" is a misleading label. That is a harder
> > question if you look too closely at the deails and consider
> > inhomogeneous and brecciated ordinary chondrites. That can all become
> > somewhat unique if you ask the right person. Then there are the motley
> > crew of ungrouped ordinary chondrites where it is hard to generalize.
> > Some may be a weak classification while others might truly be weird
> > ("rare").
> >
> > Just a few notes: the H7, L7, LL7 types are not widely used in the
> > literature and border on impact melts, so I'd take them with a grain
> > of salt unless someone goes postal on me in which case they are right
> > in whatever they say. The way I listed these, the meteorites are
> > counted by the lowest number and won't show up in the higher thermal
> > (metamorphosed) levels. In other words, for example, an LL3.8-6 is
> > counted with the LL3's.
> >
> > If you have a special meteorite, it can sometimes be a "rarer" type if
> > you start to split hairs, like H3.8 instead of just grouping it within
> > the H3's, but there is some degree of arbitrariness to this. The
> > tendency is that more virgin Solar system stuff (closer and closer
> > 3.00) is more special and like a holy grail ("rare" in a sense) to
> > some who study that - since it is more representative of the original
> > material before water and heat were added and did their thing. From
> > hat we can try to get the proof we need to work out early formation
> > processes and theorize on the related dynamics happening. By this
> > logic, and considering it is a very studied meteorite, the precious
> > meteorite SEMARKONA (LL3.00 or is it 3.01 :-)), a witnessed fall from
> > India, is rather unique being the only one with that 3.00
> > classification, which makes it super intact since formation and
> > especially interesting to experts, and most notably Dr. Jeff Grossman
> > who reviewed and updated its classification upon careful study.
> >
> > By another measure, the "common" ordinary chondrite, L5, Canadian
> > witnessed fall, VILNA, is one of those very few special meteorites
> > that was imaged during atmospheric entry and a precise orbit was
> > determined. It was not too far from Buzzard Coulee, and what makes it
> > even more special is that it was classified from a (although witnesses
> > heard pieces whizzing around) 94 milligram fragment with fusion crust.
> > The only other specimen found was a 48 milligram piece! This becomes a
> > wild anecdote of a meteorite tale when one considers that the bolide
> > passed directly over the only camera recording the sky for 500 miles
> > (over 800 km) and headed for the newly constructed and world's only
> > UFO landing site which had been built for the Canadian Centennial
> > exposition in St. Paul, Alberta, where it showered sparks
> > ("retro-rockets" to some folks). In case you wondered, I believe the
> > Japanese classified on Antarctic meteorite with 10 milligrams, if you
> > can believe that!
> >
> > So what actually makes a meteorite rare can turn into a matter of
> > semantics and who you ask. Even the scale of 3 to 6 (or 7) is somewhat
> > arbitrary and just looks for convenient thermally changed cairns along
> > the path toward melting. So if we went the other way, if H, L, and LL
> > correspond to only three parent bodies, the frequency of the types
> > follows:
> >
> > H 45.0%
> > L 40.6%
> > LL 14.3%
> >
> > Hope this helps a little with that general question!
> >
> > Kind wishes,
> > Doug
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: Melanie Matthews <miss_meteorite at yahoo.ca>
> > To: meteorite-list at meteoritecentral.com
> > Sent: Tue, Dec 15, 2009 7:01 am
> > Subject: [meteorite-list] Ordinary chondrites - rarest to the most
> > common classes
> >
> >
> > G'mornin' listites,,
> > What is the least common type of ordinary chondrite, as well as the
> > most common?
> >
> >
> >
> > Thanks
> > -----------
> > Melanie
> > IMCA: 2975
> > eBay: metmel2775
> > Known on SkyRock Cafe as SpaceCollector09
> >
> > Unclassified meteorites are like a box of chocolates... you never know
> > what
> > you're gonna get!
> >
> >
> >
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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
>
>
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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 Wed 16 Dec 2009 10:26:00 AM PST