[meteorite-list] H2 or L2 CLASS METEORITES

[Jeff Grossman]

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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>
>
>
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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