[meteorite-list] H2 or L2 CLASS METEORITES

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu, 29 Mar 2007 21:26:27 -0500
Message-ID: <OF16A7186F.E6FCFA6F-ON852572AE.0007EBD9_at_usgs.gov>

No, and there probably never will be, at least I don't think such a
classification would ever be widely accepted.

"Type 2" is an old convention, and has only ever been applied to
carbonaceous chondrites. It originated with Wiik (1956), who divided
the carbonaceous chondrites into 3 chemical groups, I, II, and
III. Group II had ~13 wt% H2O, no metal, and a lot of FeS. The
meteorites of this type were Cold Bokkeveld, Nogoya, Mighei,
Nawapali, Haripura, Santa Cruz, Murray, and Boriskino, all of which
we now call CM2.

In 1967, Van Schmus and Wood wrote the landmark paper that
established the modern petrologic types. The unequilibrated
chondrites were divided into types 1, 2, and 3, basically along the
same lines as Wiik's roman-numeral classes for carbonaceous
chondrites. Type 2 was specifically tailored to encompass Wiik's
group II, and defined as having abundant fine-grained matrix, 4-18
wt% H2O, low metal, and Ni-bearing sulfides. All of the meteorites
called type 2 by Van Schmus and Wood were again our modern CM2
chondrites, with the addition of Al Rais and Renazzo (which we now
call CR2), and Kaba (which is no longer called type 2).

Ordinary chondrites could not strictly be called type 2, even if one
was found that was water-rich: they don't have enough matrix and have
too much metal to fit the old petrologic definition, which was
customized for only CM and CR carbonaceous chondrites. In fact,
Semarkona does have hydrous minerals, especially in its matrix, and I
know that a number of my colleagues have been tempted to call it type
2 (including Sears et al., 1980, of which I am an "al"). But that
would have caused a classification crisis in ordinary chondrite
nomenclature since the petrologic types of those groups designate
something quite different: they are strictly a metamorphic
sequence. So it just wasn't done. Semarkona has stayed a type 3,
despite the fact that it has probably experienced a similar degree of
alteration as some CR2s. It's really just a matter of tradition at
this point.

Jeff



At 06:57 PM 3/29/2007, steve arnold wrote:
>Hi list.I was thinking about this today and I have not
>had time to research it.Are there any H2 or L2 class
>meteorites that have been classified?This is a real
>must thread for me.Any help would be welcome.
>
>
>
>
>steve arnold,chicago
>
>Steve R.Arnold,chicago,Ill,Usa!!
> Collecting Meteorites since 06/19/1999!!
> www.chicagometeorites.net
> Ebay I.D. Illinoismeteorites
>
>
>
>
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Dr. Jeffrey N. Grossman phone: (703) 648-6184
US Geological Survey fax: (703) 648-6383
954 National Center
Reston, VA 20192, USA
Received on Thu 29 Mar 2007 10:26:27 PM PDT