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>

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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


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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 &amp; 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 &quot;clan&quot; 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.&nbsp; 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.&nbsp;&nbsp;&nbsp; Nobody would or should ever put these in the same
group.<br><br>
&quot;Groups,&quot; 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.&nbsp; 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.&nbsp; (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 &quot;CB&quot; chondrite group.) <br><br>
Above both of these are &quot;classes,&quot; which for chondrites include
ordinary, carbonaceous, and enstatite.&nbsp; I would put R chondrites in
the ordinary class, but others prefer to call it its own class.&nbsp; K
chondrites also may or may not belong in their own class.&nbsp; Classes
are related by broad chemical properties, especially oxidation state of
Fe and ratios between various major elements.&nbsp; Classes may comprise
more than one clan and many groups.&nbsp; Classes convey even broader
relationships than clans, and possibly indicate the general region or
heliocentric distance at which the chondrites formed.&nbsp; <br><br>
Your proposal to use terms like CRH, CRL, etc., would essentially elevate
the CR clan to &quot;class&quot; status.&nbsp; I don't think this is
appropriate.&nbsp; It could also be considered an attempt to formalize
&quot;clan&quot; 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).&nbsp; <br><br>
jeff<br>
<x-sigsep><p></x-sigsep>
Dr. Jeffrey N. Grossman&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; phone: (703)
648-6184<br>
US Geological
Survey&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
fax:&nbsp;&nbsp; (703) 648-6383<br>
954 National Center<br>
Reston, VA 20192, USA<br><br>
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Received on Tue 16 Sep 2003 08:14:02 AM PDT


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