Re-4: [meteorite-list] Native iron in DHO 007

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Tue Aug 3 14:24:20 2004
Message-ID: <DIIE.0000003300002617_at_paulinet.de>

Thank you, J?rn!

> Herbert Palme et al. (1988) Camel Donga - A eucrite
> with high metal contents (Meteoritics vol. 23, pp. 49-57).

Here are some interesting pieces from that article:

Abstract (excerpt): The Camel Donga eucrite is
unique since it contains about 2% metallic iron.

Introduction (excerpt): Most eucrites contain a small amount
of metallic iron which either formed during crystallization of
the eucritic magma or by some reduction of oxidized iron
in pyroxene (Duke, 1965*).

Rare gases in Camel Donga (excerpt): The formation of metallic
iron did not occur late in the history of Camel Donga.

Discussion - Origin of metallic iron (excerpts):

There are several possibilities for the origin of the metal:

a) a foreign metal component was introduced into the meteorite.

b) A decrease occurred in oxygen partial pressure during or after
cooling of the eucrite magma, resulting in reduction of Fe in the silicates.

c) Loss of S and/or SO^2 from sulfides occurred at elevated temperatures

Textural evidence suggests that the Camel Donga metal was most likely
formed by reduction of pyroxene after this mineral had completely crystallized.

Model for the formation of metal (excerpts): Camel Donga is a brecciated eucrite,
similar to Stannern or Juvinas, though with a relatively high content of S (ca. 0.5 %).
This breccia was formed by an impact, causing reheating, perhaps in an ejecta
blanket, to around 1000?C. Volatilized S and SO^2 escaped, reducing oxidized
iron to metal.

The large amount of metal in Camel Donga seems to require a unique process of
formation. However, the frequent occurrence of metal associated with pyroxene in
other eucrites (Duke, 1965*) suggests similar processes, although to a much
smaller extent.

*DUKE M. (1965) Metallic iron in basaltic achondrites
(J. Geophys. Res. 70, 1523-1527).


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Received on Tue 03 Aug 2004 02:24:08 PM PDT