[meteorite-list] Re: Mercury Meteorite Puzzle

From: Rhett Bourland <rbourlan_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:50 2004
Message-ID: <IOEBKAHMGFBDJMOFGDFNEEEPDLAA.rbourlan_at_evansville.net>

Another thing that has always bugged me and I can't understand is if the
irons are supposed to be the core of a large differentiated asteroid, why
don't we see more types of pallasites? There are dozens of irons classes
when you include the assorted anomolous irons out there but there are only a
few types of pallasites (main group, pyroxene, Eagle Station grouplet,
Glorietta Mountain, and few other anoms.). There are some studies ("A
nonmagmatic origin of group-IIE iron meteorites" by John Wasson and Jianmin
Wang, in which they also mention that the IAB and IIICD irons could be
formed by localized melting instead of core formation) that have been done
to show that some irons could be formed in a localized melt pocket but if
the majority of irons are from the core its seems to me there should be more
pallasite groups.
Yet another great mystery in the world of meteorites! If anyone could shed
some light on this please share.
Best wishes,
Rhett Bourland
www.asteroidmodels.com
www.asteroidmodels.com/personal
www.meteoritecollectors.org

-----Original Message-----
From: meteorite-list-admin_at_meteoritecentral.com
[mailto:meteorite-list-admin_at_meteoritecentral.com]On Behalf Of
Starbits_at_aol.com
Sent: Saturday, May 18, 2002 12:32 PM
To: meteorite-list_at_meteoritecentral.com
Subject: [meteorite-list] Re: Mercury Meteorite Puzzle


Ron Baalke wrote:

<Since Mercury and Venus are inside of Earth's orbit, then by the process of
elimination, that would indicate the parent body for E chondrites are either
Mercury or Venus. OK, fair enough.>

and

<While it is still possible the parent body for the E chondrites and NWA 011
may
be Mercury or Venus, you can't rule out asteroids just yet either. >

Both of these statements are incorrect. Both Mercury and Venus are
differentiated bodies. Neither can be the source of "chondrites" of any
kind. They could however the the source of various "achondrites".

If people are interested in a mystery here is a big one. Pallasites are
generally
assumed to be from the core / mantle boundry. There are quite a few
pallasites
so their formation doesn't appear to be an unusual occurance. There are
also a
lot of irons from the core side of the boundry. There are however no, as
in
zero, meteorites with pallasitic type olivine crystals with out an iron
matrix.
The mantle by volume would be larger than the core of most differentiated
bodies. So where are the olivine meteorites? One would think they would be
at least as abundent as the pallasites. Is the pallasite theory incorrect?
Is there
a yet undiscovered class of meteorites? Is there a mechanism that prevents
the formation of a pure olivine region or destroys them after formation,
preventing
a pure olivine meteorite from reaching earth? There are no answers. The
big mystery isn't whether we have a meteorite from mecury, it is where is
the
olivine?

Eric Olson
http://www.star-bits.com

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Received on Sat 18 May 2002 10:58:16 PM PDT