[meteorite-list] metal-rich diogenite vs mesosiderite-C

From: David Weir <dgweir_at_meteoritecentral.com>
Date: Fri Sep 17 15:00:25 2004
Message-ID: <414B342E.530FC620_at_earthlink.net>

Hello J?rn,

Since nobody "in the know" has answered your ponderings yet, I think
I'll add my take on this circumstance. I followed the progress of
analysis of NWA 1827 because I had seen the piece that Nelson had
acquired and I thought it had a unique and interesting appearance. The
preliminary analysis had considered that the data best fit a
classification as a recrystallized, metal-rich diogenite, which was
intruded by an exotic metallic body and annealed within a deep regolith.

In a paper by R. Hewins (1988) a similar description was given for
RKPA79015, but which was taken to be a diogenitic end member of the
mesosiderite body. In a similar way, Clark and Mason (1982) had much
difficulty in their original attempt to classify RKPA79015 (Haack <i>et
al.</i>, 1996). They finally used the widths of tetrataenite rims on
taenite to arrive at a classification of mesosiderite for this
meteorite.

Anyway, after extended analyses scientists at NAU determined that NWA
1827 is also consistent with a type 2C meso, fantastic news for us type
collectors (I guess this is still tentative though).

In addition, the abstract to which you refer I believe was the final
result of a joint effort by both labs (NAU and UWS), which superseded
the original classification of NWA 1982, now thought to be more likely
paired with this type 2C meso. That's my take.

There is further information on the many difficulties of classifying
this type 2C meso on my NWA 1827 webpage.

David

----------------------original post--------------------------------

It seems, there is a problem with the class C mesosiderites and the
metal-rich diogenites, which may just be fragments of the same meteorite
shower.

In the last Met. Bulletin 88, the following classifications and remarks
are given:

NWA 1982: an ungrouped achondrite "not paired with NWA 1827 or NWA 1879
mesosiderite"

NWA 1827: mesosiderite (tentatively classified C) "resembles a
metal-rich diogenite... [but is] part of a large, heterogeneous
mesosiderite containing sparse eucritic and diogenitic clasts"

In the abstract by T. E. Bunch et al. (2003) MAPS 39, no. 8 (Suppl.),
p.A19, which is the same MAPS issue with the Bulletin 88, the authors
conclude that NWA 1827 and NWA 1982 are paired and that they "could be
misidentified as "metal-rich diogenite."

So, at least for NWA 1982, we have a clear ambiguity between these two
references.

Best regards,

J?rn
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Received on Fri 17 Sep 2004 02:59:58 PM PDT