While we're at it, what's the difference between a "3" and a "3.0?" Does a "3" imply that no one made any finer discrimination? Or does a "3" imply that it's really a "3.0?" Cheers, Nick
At 08:23 AM 4/14/2004, Jörn Koblitz wrote:
Dear Pierre,
> I've got a (stupid ?) question about the classification of > the chondrites. > > What is the difference between this kind of classification : > For example L3.6, L3-6 or H5/6 > > Is the sign "-" the same as "/" or "." in this case ?
Regarding the use of hyphens and slashes, see the postings to the list of March 19 to 23 (pasted below).
The use of "." in the classification (e.g. L3.6) is used in case that a petrologic SUBtype has been obtained, either by measuring the induced thermoluminescence (TL) or by calculation of the percentage mean deviation (PMD) of the fayalite and ferrosilite contents of olivine and pyroxene, respectively, measured by microprobe (EPMA). The subtype is just a finer subdivision and is only used for unequilibrated (i.e. type 3) chondrites. It is a scale for the amount of thermal metamorphism a chondrite has experiences since its accretion. In this respect, a 3.0 indicate the least metamorphosed (or most primitive / less heated) type 3 chondrite. On the other hand, a type 3.9 chondrite is almost chemically equilibrated like type 4 and higher, as it has experienced considerable heating (e.g. by impact shock) during its lifetime on the parent-body (planetesimal or asteroid).
Hope this answers your question.
Best regards,
Joern
_______________________________________________________________________________ Joern Koblitz MetBase Editor The MetBase Library of Meteoritics and Planetary Sciences Benquestrasse 27 D-28209 Bremen, Germany phone: +49 421 24 100 24 fax: +49 421 24 100 99 email: [EMAIL PROTECTED] _______________________________________________________________________________
Hello John, David and Bernd,
Sorry for my late reply - I'm not online on weekends.
You are right, it's a messy situation with the use of slashes "/" and hyphens "-" and as Jeff outlined long time ago, it actually depends on the research group who does the classification. With MetBase, I stick to the presently preferred rules that "/" indicates a transitional type and "-" a breccia. However, as complicated as it could be, imagine that a transitional group like H/L contains clasts of different petrologic types, e.g. 4 and 6: should it then be designated H/L4-6 or (H/L)4-6 or H4-6/L4-6?
Regarding the transitional petrologic type designations, e.g. H5/6: beware that there is always a personal bias by the person who did the classifications: one researcher will classify an H chondrite H5, another researcher the same chondrite H6 and a third person would give it H5/6: there is always an uncertainty of +/- 0.5 for equilibrated ordinary chondrites. That's why some researchers think that it is always appropriate to assign straight numbers and to prevent transitional numbers, which is rather a sign of shakiness. Regarding the use of parentheses, e.g. "LL/(L)3" or "LL(L)3": this problem is rather restricted to very unequilibrated chondrites as Jeff pointed out. Since highly unequilibrated chondrites show large variations in mineral chemistry (e.g. wide ranges of olivine, pyroxene or metal compositions), one has to do a large number of microprobe and (oxygen) isotopic measurements to gain certainty on the classification. This is very time-consuming and expensive. Further, many hot-desert finds are higly weathered which makes it difficult to classify them based on chemical compositions (terrestrial contamination).
David: Regarding the differences in designations beween Met. Bulletin and MetBase, I have to check the literature sources of the MetBase information and let you know lateron if I can clearify.
Joern
> -----Ursprüngliche Nachricht----- > Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Gesendet: Freitag, 19. März 2004 22:27 > An: [EMAIL PROTECTED] > Cc: [EMAIL PROTECTED]; Jörn Koblitz; > [EMAIL PROTECTED] > Betreff: Re: [meteorite-list] Hyphens / Slashes > > > Bernd. Dave, Joern and others, > > Bernd, thanx for the previously submitted info from Jeff on > slashes and dashes. > > That should certainly clear it up the confusion, right Dave. :) > > John > > BTW: Joern...in all seriousness I really appreciate you > responding to this thread. > > > > > For chondrite groups, petrologic types, shock stages, and > weathering > > > grades, slashes (e.g., H5/6) indicate transitional > assignments. Hyphens > > > in petrologic type assignments for chondrites (e.g., > H5-6) indicate the > > > range of types observed in breccias. Group names such as > "L(LL)" indicate > > > uncertain assignments, with the less probable group in > parentheses. > > > > Hello All, > > > > I was waiting for Jeff Grossman to chime in here, because > > on Monday, 07 Sep 1998, Jeff wrote to this to the List (excerpts): > > > > Right now we have a literature polluted with this and other > nomenclatures > > (like using a "/" instead of a "-" for the same thing), and > the community has > > no way of looking at a catalog and knowing what's what. The > Meteorite > > Nomenclature committee has no jurisdiction over meteorite > classification; > > it just oversees meteorite names. It's just a mess. > > > > There is NO convention for naming brecciated chondrites. > Many, including the > > group at Muenster, like to use a slash to separate > components of a breccia. > > However, nobody has ever written a paper on the subject, > and the rules are up > > for grabs. I happen to be of the opinion that the slash is > ridiculous for many > > reasons, > > including the one brought up here: we will always need to > be reclassifying > > breccias > > whenever somebody finds a new lithology among the clasts. > This is not feasible. > > > > These parentheses are used by some researchers when they > cannot determine with > > certainty the group assignment of a meteorite. L(LL)3 means > that they lean > > towards > > L3, but it could be an LL3. Indeed, it is very difficult to > differentiate > > between L3 and LL3 > > chondrites, as they may have similar sized chondrules, > similar metallography, > > similar > > silicate compositions (i.e., highly heterogeneous), and > even oxygen isotope > > compositions > > and trace elements cannot always resolve them well. Even > some of the most > > famous, best > > studied meteorites have been given various classifications > in different parts of > > the literature > > (e.g., Tieschitz, Krymka, Bishunpur). > > > > If any meteorite has been called "LL/(L)3", I have no clue > what this means. > > > > > > To: [EMAIL PROTECTED] > > [EMAIL PROTECTED] > > Cc: [EMAIL PROTECTED] > > > > > > ______________________________________________ > > Meteorite-list mailing list > > [EMAIL PROTECTED] > > http://www.pairlist.net/mailman/listinfo/meteorite-list >
> -----Ursprüngliche Nachricht----- > Von: Pierre-Marie PELE [mailto:[EMAIL PROTECTED] > Gesendet: Mittwoch, 14. April 2004 08:15 > An: [EMAIL PROTECTED] > Betreff: [meteorite-list] Classification question > > > Hello to the List ! > > I've got a (stupid ?) question about the classification of > the chondrites. > > What is the difference between this kind of classification : > For example L3.6, L3-6 or H5/6 > > Is the sign "-" the same as "/" or "." in this case ? > > Thanks a lot, > > Pierre > ------------------------------------------ > > Faites un voeu et puis Voila ! www.voila.fr > > > > ______________________________________________ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://www.pairlist.net/mailman/listinfo/meteorite-list >
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