[meteorite-list] Rocks from Space Picture of the Day - April 12, 2010

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 12 Apr 2010 17:41:57 UT
Message-ID: <DIIE.00000084000048A1_at_paulinet.de>

Richard wrote: "Beautiful Laurence!"
Jeff K. wrote: "WOW!!!"

http://www.rocksfromspace.org/April_12_2010.html


Hello Laurence, Richard, Jeff and List,

This is an exceptionally beautiful "polysomatic" barred olivine chondrule!
The unusual pentagonal arrangement of the olivine bars may be the result
of a euhedral olivine crystal at the center of these 5 sets of parallel olivine
bars. The contours of the (almost) euhedral crystal are still readily recognizable.
The crystal itself is either in optical extinction in this photo or it is no longer
there.

Instead of growing inward from the once molten droplet (which would have
resulted in a "normal" barred olivine chondrule), the bars probably grew
along the sides of the (almost) euhedral crystal at its center.

*If* I am right with these suppositions, the subhedral crystal at the center
had already solidified when the pentagonal bars started growing and thus served
as a "nucleus" along whose sides the bars grew the way we see them in the pic.

The different interference colors of the pentagonal bars are due to the fact
that they are oriented at different angles to each other.

An almost identical polysomatic BO chondrule can be admired on p. 114
of our late Richard Norton's Encyclopedia of Meteorites!


Best wishes,

Bernd
Received on Mon 12 Apr 2010 01:41:57 PM PDT