[meteorite-list] Ordinary chondrites - decimal metamorphic grade question
Darryl Pitt
darryl at dof3.com
Thu Dec 17 08:19:33 EST 2009
Good Morning,
Thank you so much for this! Finally get the nuances...
Darryl
On Dec 17, 2009, at 5:50 AM, Jeff Grossman wrote:
> 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
>>> >>
>>> >>
>>> >> -----Ursprüngliche 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
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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
>>
>>
>> ______________________________________________
>> 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
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