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

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu, 17 Dec 2009 05:50:09 -0500
Message-ID: <OFFB6954EB.0675413E-ON0525768F.003B8C01_at_usgs.gov>

Types 2 and 3 are describing two different
parameters. Type 2 (and 1) means that a
meteorite has experienced aqueous
alteration. Because such effects are prominent
in the CI, CM and CR groups, nearly all of them
are traditionally (since the 1960s) described as
types 1 and 2. Types 3-6 are traditionally used
to describe metamorphic effects in chondrite
groups where thermal processing has been
important, such as CO, CV, CK, OCs, ECs,
etc. Although most meteorites in the first list
above are hydrated but unmetamorphosed and most
meteorites in the second list are metamorphosed
but unhydrated, there is crossover that leaves us
without an adequate vocabulary to describe. Some
CM and related chondrites have been heated to
levels similar to a type 3.2 chondrite, yet they
are still called type 2 due to alteration. Some
low-type-3 ordinary and CV chondrites have
hydrated phases and Ni-bearing sulfides like a
type 2 chondrite might, yet they are called type
3.0 to distinguish them from more-heated group members.

So, when I say that most CR chondrites are type
3.00, I mean that their thermal histories are
similar to those of type 3.00 ordinary or CO
chondrites; they have never gotten very hot for
very long. But most CR chondrites are ALSO type
2. Most CM chondrites are type 2 (alteration)
AND type 3.00 (metamorphism). But somehow,
alteration trumps metamorphism for carbonaceous
chondrites and nobody calls them type 3.00 even
thought this describes them well. Strangely, when
a CR chondrite lacks alteration, many people are
happy to call it type 3 (e.g., MET 00426). But
when an ordinary chondrite is hydrated, nobody
would ever think of calling it type 2 (e.g., Semarkona).

This is called a lousy nomenclature system.

jeff g.

At 05:25 AM 12/17/2009, Jeff Kuyken wrote:
>Hi Jeff,
>
>Inrteresting stuff indeed. One thing just caught
>my attention though. You mentioned that "CR
>chondrites which are mostly type 3.00" which I
>have not heard of before. The Met Bull lists
>nearly all as CR2, some as just CR and an odd
>CR1. My crude understanding of type-2 vs type-3
>is that type-2 never received thermal alteration
>whereas type-3 is where that starts. Am I wrong there?
>
>So would CR3.00 tell us that the particular
>meteorite in question did not go through any
>thermal metamorphism? How would that vary from CR2?
>
>Thanks,
>
>Jeff
>
>
>----- Original Message ----- From: "Jeff Grossman" <jgrossman at usgs.gov>
>To: <Meteorite-list at meteoritecentral.com>
>Sent: Thursday, December 17, 2009 3:12 AM
>Subject: Re: [meteorite-list] Ordinary
>chondrites - decimal metamorphic grade question
>
>
>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
>
>
>______________________________________________
>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
Received on Thu 17 Dec 2009 05:50:09 AM PST