[meteorite-list] Ordinary chondrites - decimal metamorphic grade question

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Wed, 16 Dec 2009 11:29:59 -0500
Message-ID: <OF72E2197F.84B2B8AD-ON0525768E.005AA8E6_at_usgs.gov>

p.s.: I can determine the 3.00-3.05-3.10-3.15
subtypes reasonably well on most ordinary
chondrites using a thin section and a petrographic microscope.

jeff

>The hundredths place is only defined for type 3s
>that are lower than type 3.2. This is because
>there is a lot of variation in metamorphic
>effects in the low end of the range, too much to
>cram into just types 3.0 and 3.1. Initially, I
>define 4 new classes: 3.00, 3.05, 3.10 and 3.15
>(Grossman and Brearley 2005, in
>MAPS). Subsequently Kimura, I and others have
>realized that there are subtle variations that
>may require more categories between 3.00 and
>3.05, e.g. Semarkona as a type 3.01, as compared
>with CR chondrites which are mostly type 3.00.
>
>You do not need specialized equipment other than
>an electron microprobe to determine
>this. However, with high-resolution FE-SEM
>imaging, you can see structures in the metal and
>olivine that also give this classification
>information. Raman spectroscopy also helps classify meteorites in this range.
>
>Jeff


At 11:04 AM 12/16/2009, Matt Morgan wrote:
>Since Darryl brought up his incredible LL3.05, I
>have to ask how does/can one classify the
>metamorphic grade to the to the tenths or now
>the hundredths of a decimal? I have had some
>tell me this is subjective and others say you
>need specialized equipment. Please, any researchers, explain.
>
>Darryl-
>I don't mean to pick on your material, but it is
>a question that has been nagging me for sometime and you stirred my brain!
>
>Thanks in advance!
>Matt
>----------------------
>Matt Morgan
>Mile High Meteorites
>http://www.mhmeteorites.com
>P.O. Box 151293
>Lakewood, CO 80215 USA
>
>-----Original Message-----
>From: Darryl Pitt <darryl at dof3.com>
>Date: Wed, 16 Dec 2009 10:35:38
>To: Jeff Grossman<jgrossman at usgs.gov>
>Cc: <Meteorite-list at meteoritecentral.com>
>Subject: Re: [meteorite-list] Ordinary chondrites - rarest to the most
> common classes
>
>
>
>Get ready for NWA 5717.....
>
>Initially "anomalous," the classification had to be changed to
>"ungrouped" as it was too difficult to determine what it was anomalous
>to. 3.05 subtype. More to follow....
>
>
>
>
>
>On Dec 16, 2009, at 10:26 AM, Jeff Grossman wrote:
>
> > 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!
> >> >
> >> >
> >> >
> >> >__________________________________________________________________
> >> > Looking for the perfect gift? Give the gift of Flickr!
> >> >
> >> > http://www.flickr.com/gift/
> >> >
> >> >______________________________________________
> >> > http://www.meteoritecentral.com
> >> > Meteorite-list mailing list
> >> > Meteorite-list at meteoritecentral.com
> >> > http://six.pairlist.net/mailman/listinfo/meteorite-list
> >> >
> >> >______________________________________________
> >> > http://www.meteoritecentral.com
> >> > Meteorite-list mailing list
> >> > Meteorite-list at meteoritecentral.com
> >> > http://six.pairlist.net/mailman/listinfo/meteorite-list
> >> >
> >>
> >>
> >> --
> >> Dr. Jeffrey N. Grossman phone: (703) 648-6184
> >> US Geological Survey fax: (703) 648-6383
> >> 954 National Center
> >> Reston, VA 20192, USA
> >>
> >>
> >>______________________________________________
> >> http://www.meteoritecentral.com
> >> Meteorite-list mailing list
> >> Meteorite-list at meteoritecentral.com
> >> http://six.pairlist.net/mailman/listinfo/meteorite-list
> >>
> >>______________________________________________
> >> http://www.meteoritecentral.com
> >> Meteorite-list mailing list
> >> Meteorite-list at meteoritecentral.com
> >> http://six.pairlist.net/mailman/listinfo/meteorite-list
> >
> > Dr. Jeffrey N. Grossman phone: (703) 648-6184
> > US Geological Survey fax: (703) 648-6383
> > 954 National Center
> > Reston, VA 20192, USA
> >
> >
> >______________________________________________
> > http://www.meteoritecentral.com
> > Meteorite-list mailing list
> > Meteorite-list at meteoritecentral.com
> > http://six.pairlist.net/mailman/listinfo/meteorite-list
>
>______________________________________________
>http://www.meteoritecentral.com
>Meteorite-list mailing list
>Meteorite-list at meteoritecentral.com
>http://six.pairlist.net/mailman/listinfo/meteorite-list

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 11:29:59 AM PST