[meteorite-list] Polymict EUC vs. HOW - NWA1109 question

[Jeff Grossman]

Here's a quote from Mittlefehldt's article in the 1998 Planetary Materials 
volume:

"Howardites have long been known to be polymict breccias (Wahl 1952).  More 
recently, numerous polymict breccias with bulk compositions like those of 
eucrites have been recovered from Antarctica, leading to recognition of 
polymict eucrites as a distinct rock type (e.g. Miyamoto et al. 1978; Olsen 
et al. 1978; Takeda et al. 1978).  Diogenites with basaltic eucritic clasts 
are also known (Lomena et al. 1976), and it has thus become obvious that, 
in terms of major components, howardites are intermediate members of an 
essentially continuous sequence of polymict breccias, including polymict 
eucrites and polymict diogenites (Delaney et al. 1983), that extends from 
the monomict eucrites to the monomict diogenites."

Here's the Delaney article from 1983, which defines the 10% cutoff of 
diogenitic clasts in howardites:

http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1983Metic..18..103D

This is not my field of expertise, but it seems that the key word in all of 
this is "continuous."  It is entirely possible that separate fragments of 
paired stones could receive somewhat different classifications, especially 
if only small areas of heterogeneous objects are examined.  It's also 
possible that they're not paired (NWA 1553 has not been officially described).

jeff

At 11:13 AM 5/26/2004, Adam Hupe wrote:
>Hi Martin and List,
>
>NWA1109 is definitely a eucrite as it has no diogenite component.  We 
>stated this several times and posted publicly to the List so if somebody 
>is still selling it as a Howardite than they are ignoring the scientists 
>who studied it.
>
>All the best,
>
>
>----- Original Message -----
>From: <mailto:Altmann at Meteorite-Martin.de>Martin Altmann
>To: 
><mailto:meteorite-list at meteoritecentral.com>meteorite-list at meteoritecentral.com 
>
>Sent: Wednesday, May 26, 2004 6:36 AM
>Subject: [meteorite-list] Polymict EUC vs. HOW - NWA1109 question
>
>Hello list,
>
>has anyone an idea, which of the finds paired with NWA1109 are classified 
>as howardites?
>NWA1109 is listed in the Bulletin as polymict eucrite.
>Some sell it as howardite, some as howardite or eucrite, some as eucrite.
>
>Thanks!
>Martin
>
>
>----------
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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

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