"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: Martin Altmann
- To: [EMAIL PROTECTED]
- 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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