Re-2: [meteorite-list] CH or CB Chondrite?

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:56 2004
Message-ID: <20030916234313.DD49D53532_at_pairlist.net>

Jeff,

Thank you for the explanation and clarification that clans do not necessarily
tie two groups together...though they are thought to be related due to
similarities. So it goes something like this... (with a few questions at the
bottom).

Class: Carbonaceous

   Groups: CB3a, CB3b, CH, CR2 (CR clan)
           CV3, CK3-5 (CV-CK clan)
           CM2, CO3 (CM-CO clan)
           CI
and

Class: Ordinary Chondrites

   Groups: H (with in between samples of H/L and L/LL)
           L
           LL
           R (Jeff's point)

w/K in its' own Class, or as a Group in either the C or OC Class ? (also
Jeff's point)

Note 1: Raising CR to a Class level does not make sense looking at this
model. My (John D's suggestion) was actually to have CR as a Group and the
CRH, CRL, CRB, CH as subgroups(or class or even type ?)...which also looks
inappropriate.

Note 2: I've seen CH called CH2...is that not the case as of yet???

Note 3: I've seen Classes called Groups in one textbook.

Note 4: Are subgroups appropriately called a class or should they be a type
(ie: Class OC, Group H, class or type H3.8 ???) Some texts call H3.8 a
class...which makes it even more confusing! Should it be a type?


Thanks again Jeff,

John D.

> 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
>
Received on Tue 16 Sep 2003 07:43:10 PM PDT