Re-2: [meteorite-list] CH or CB Chondrite?
From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:56 2004 Message-ID: <5.1.0.14.2.20030916072617.02fca3e0_at_gsvaresm02.er.usgs.gov> --=====================_410367250==_.ALT Content-Type: text/plain; charset="us-ascii"; format=flowed At 10:30 PM 9/15/2003, j.divelbiss_at_att.net wrote: >2. If all these variations on CB's and CH's are actually part of the CR clan, >then why don't we start with calling them CR's, and then give them a suffix >of some kind to differentiate them CRL(low metal), CRB-1 and CRB-2, CRH(high >metal), etc.. Designations of CBa & b, CH, CR, and who knows what next...all >under one umbrella(CR clan) does not make sense to this simpleton. Kinda like >what we are heading for with olivine diogenites. I know tradition, known >name, etc. Change before it is too late!!! When we say "clan" we mean a number of meteorite groups that are related, not closely enough to be a single group, but by sharing enough properties that it seems likely they formed in a similar way or in a similar time or place (it's all very vague). It's a very loose term meant to convey a relationship. Bencubbin and Renazzo look nothing like each other, but share certain chemical and isotopic properties than lead researchers to place them in the same clan. Nobody would or should ever put these in the same group. "Groups," on the other hand, refer to groups of meteorites that are alike in most of their primary properties (chemistry, texture, isotope systematics), and which probably formed together in one parent body. If you show an expert two members of the same group with identical secondary histories (metamorphic, shock, aqueous alteration, and terrestrial weathering), in most cases he/she would have a very hard time telling them apart. (Of course, a 4-year-old could tell Bencubbin apart from QUE 94411, which is part of the reason I object to putting them in the same "CB" chondrite group.) Above both of these are "classes," which for chondrites include ordinary, carbonaceous, and enstatite. I would put R chondrites in the ordinary class, but others prefer to call it its own class. K chondrites also may or may not belong in their own class. Classes are related by broad chemical properties, especially oxidation state of Fe and ratios between various major elements. Classes may comprise more than one clan and many groups. Classes convey even broader relationships than clans, and possibly indicate the general region or heliocentric distance at which the chondrites formed. Your proposal to use terms like CRH, CRL, etc., would essentially elevate the CR clan to "class" status. I don't think this is appropriate. It could also be considered an attempt to formalize "clan" nomenclature, but clans are so loose and poorly defined that this is not practical (AND, it would require renaming many other chondrites, like the clans CV-CK, CM-CO, and H-L-LL). jeff Dr. Jeffrey N. Grossman phone: (703) 648-6184 US Geological Survey fax: (703) 648-6383 954 National Center Reston, VA 20192, USA --=====================_410367250==_.ALT Content-Type: text/html; charset="us-ascii" <html> At 10:30 PM 9/15/2003, j.divelbiss_at_att.net wrote:<br> <blockquote type=cite class=cite cite>2. If all these variations on CB's and CH's are actually part of the CR clan, <br> then why don't we start with calling them CR's, and then give them a suffix <br> of some kind to differentiate them CRL(low metal), CRB-1 and CRB-2, CRH(high <br> metal), etc.. Designations of CBa & b, CH, CR, and who knows what next...all <br> under one umbrella(CR clan) does not make sense to this simpleton. Kinda like <br> what we are heading for with olivine diogenites. I know tradition, known <br> name, etc. Change before it is too late!!!</blockquote><br> When we say "clan" we mean a number of meteorite groups that are related, not closely enough to be a single group, but by sharing enough properties that it seems likely they formed in a similar way or in a similar time or place (it's all very vague). It's a <b>very </b>loose term meant to convey a relationship. Bencubbin and Renazzo look nothing like each other, but share certain chemical and isotopic properties than lead researchers to place them in the same clan. Nobody would or should ever put these in the same group.<br><br> "Groups," on the other hand, refer to groups of meteorites that are alike in most of their primary properties (chemistry, texture, isotope systematics), and which probably formed together in one parent body. If you show an expert two members of the same group with identical secondary histories (metamorphic, shock, aqueous alteration, and terrestrial weathering), in most cases he/she would have a very hard time telling them apart. (Of course, a 4-year-old could tell Bencubbin apart from QUE 94411, which is part of the reason I object to putting them in the same "CB" chondrite group.) <br><br> Above both of these are "classes," which for chondrites include ordinary, carbonaceous, and enstatite. I would put R chondrites in the ordinary class, but others prefer to call it its own class. K chondrites also may or may not belong in their own class. Classes are related by broad chemical properties, especially oxidation state of Fe and ratios between various major elements. Classes may comprise more than one clan and many groups. Classes convey even broader relationships than clans, and possibly indicate the general region or heliocentric distance at which the chondrites formed. <br><br> Your proposal to use terms like CRH, CRL, etc., would essentially elevate the CR clan to "class" status. I don't think this is appropriate. It could also be considered an attempt to formalize "clan" nomenclature, but clans are so loose and poorly defined that this is not practical (AND, it would require renaming many other chondrites, like the clans CV-CK, CM-CO, and H-L-LL). <br><br> jeff<br> <x-sigsep><p></x-sigsep> Dr. Jeffrey N. Grossman phone: (703) 648-6184<br> US Geological Survey fax: (703) 648-6383<br> 954 National Center<br> Reston, VA 20192, USA<br><br> </html> --=====================_410367250==_.ALT-- Received on Tue 16 Sep 2003 08:14:02 AM PDT |
 StumbleUpon del.icio.us reddit Yahoo MyWeb
|