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

From: Matt Morgan <mail_at_meteoritecentral.com>
Date: Wed, 16 Dec 2009 16:04:07 +0000
Message-ID: <1007140231-1260979442-cardhu_decombobulator_blackberry.rim.net-413127853-_at_bda667.bisx.prod.on.blackberry>

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!
>> >
>> >
>> >
>> >__________________________________________________________________
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>> >
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>> >
>> >______________________________________________
>> > http://www.meteoritecentral.com
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>> > Meteorite-list at meteoritecentral.com
>> > http://six.pairlist.net/mailman/listinfo/meteorite-list
>> >
>> >______________________________________________
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>> > 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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>> Meteorite-list mailing list
>> Meteorite-list at meteoritecentral.com
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>>
>>______________________________________________
>> 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

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Received on Wed 16 Dec 2009 11:04:07 AM PST