[meteorite-list] Mg/Fe+Mg of Bulk Planet

From: Frank Prochaska <fprochas_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:12 2004
Message-ID: <NDBBICFKNKHAAEEJLDALMEHMCHAA.fprochas_at_premier1.net>

Hello all!

I'm not sure that they way they are using the Mg/Fe+Mg ratio in the that
passage is referring to degree of oxidation. The bulk ratio of a planet
would be constant regardless of the extent of oxidation or reduction, just
like the bulk weight % of Fe in a meteorite sample includes all Fe whether
contained in silicates, sulfides, or as free metal. They may be using the
Mg/Fe+Mg ratio just as they do isotopic ratios of other elements, like
samarium or oxygen. The ratio of Mg to total Fe and Mg may be distinctive
between parent bodies, just as oxygen isotope ratios show distinctions
between the Earth, the Moon, and Mars. Mg and Fe cations are also nearly
the same size and have the same charge, and so act very much the same in
silicate melts, hence the olivine and pyroxene solid solutions. By knowing
the bulk ratio of the planet, you have a reference number to compare various
rocks to see if some outcrops or formations are relatively enriched or
depleted in one element or another.

Just my thoughts.

Frank Prochaska




-----Original Message-----
From: meteorite-list-admin_at_meteoritecentral.com
[mailto:meteorite-list-admin_at_meteoritecentral.com]On Behalf Of Bernd
Pauli HD
Sent: Sunday, February 25, 2001 10:10 PM
To: Robert Beauford
Cc: meteorite-list_at_meteoritecentral.com
Subject: [meteorite-list] Mg/Fe+Mg of Bulk Planet


Robert Beauford wrote:

> I'm still trying to figure out the significance of
> "Mg/Fe+Mg of Bulk Planet" in terms of planetary
> materials.

Hi All!

I don't know if the "Mg/Fe+Mg of Bulk Planet" refers to the distinction
between achondrite groups, but if it does, here is what I can offer:

The Fe/(Fe+Mg) ratio allows meteoriticists to measure the degree of
oxidation of mineral assemblages in metorites. When you plot Ca/Mg
vs. Fe/(Fe+Mg), you can easily recognize that the achondrites divide
themselves into distinct groups with clearly discernible gaps between
the aubrites, the diogenites, the howardites, the eucrites, etc.


Best wishes,

Bernd

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Received on Sun 25 Feb 2001 09:59:37 AM PST