[meteorite-list] Mica in meteorites....was Comet McNaught and Sodium

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Sun, 25 Feb 2007 15:03:40 -0800 (PST)
Message-ID: <293415.21451.qm_at_web51003.mail.yahoo.com>

--- bernd.pauli at paulinet.de wrote:
> The CV3 chondrite Grosnaja contains sodium
> phlogopite, a phyllosilicate

Well if this is so, a long standing "factoid" in the
world of meteorites falls with this finding: "Mica
does not occur in meteorites".

Seems some meteorites DO contain mica, and a mineral
species of mica that would not have been anticipated
in Bowen. The micas biotite and muscovite appear in
Bowen's reaction series while philogopite does not
(given normal availability of iron). Only in an iron
poor setting does philogopite form. In this case a
potassium substitution by sodium has also occurred.

Phlogopite (K,Mg3AlSi3O10 (F,OH)2)is the end member of
the phlogopite biotite series of mica-- usually
associated with metamorphism of marbles, igneous
intrusions such as kimberlites of diamond fame, or
found in certain magnesium rich pegmaties-- even in
basalt. These are not the sources one thinks of for
carbonaceous meteorites.

Elton
Received on Sun 25 Feb 2007 06:03:40 PM PST