[meteorite-list] Ordinary chondrites - decimal metamorphic grade question
From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Thu, 17 Dec 2009 21:25:50 +1100 Message-ID: <BE7A2D5D97234A95A46DD906A4A10773_at_JeffPC> 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 Received on Thu 17 Dec 2009 05:25:50 AM PST |
 StumbleUpon del.icio.us reddit Yahoo MyWeb
|