[meteorite-list] portales

From: David Freeman <dfreeman_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:31 2004
Message-ID: <3CFE7756.3050100_at_fascination.com>

Dear Rhett, Harlan, and List;
My portales story is...the neatest piece that I saw was half buried in a
living chunk of asphalt! And I always wondered if it was sawn out first
and permission granted second or was it guarded until saws and a plan
were gathered. This was a most amazing effort at specimen collecting
in the least.

My second portales story, my work associate has a brother that lives
there and they are all now meteorite hunters.
Long Live portales and we need a few more events just like that one!
Best,
Dave F.


Rhett Bourland wrote:

>Hi Harlan,
>First of all, good topic!!! I hope a lot of people post on this one as I'd
>love to hear what everyone has to say on it. I apologize if I get a bit
>wordy but I know a lot of people who may not know very much about meteorites
>come here to learn so I thought I'd talk a bit. If I'm too far off base on
>any of this I apologize and please let do not hesitate to correct me.
>Before I even start about how I believe it formed, I'll start off with what
>I know about it. It is an H6 chondrite which means that it formed deeper in
>the asteroid it came from than other H chondrites like H3's, H4's, and H5's.
>For a good explanation on the formation of asteroids check out "Meteorites
>and Their Parent Planets" by McSween. Almost all asteroids start off as
>"onion shells" with the more metamorphosed grades buried deeper in the
>parent body than the lower grades. This is due to the asteroid's ability to
>more easily radiate the heat from its outer layers than the more inside
>parts and thus heat is what equilibrated and altered the areas closer to the
>core more than the regions near the surface. Some asteroids, after being
>formed as an onion shell, will undergo collisions which, depending on their
>severity, will have different effects on different parent bodies. If the
>impact is severe enough then the asteroid will be shattered and pieces of it
>will go flying off in many directions and not reaccreate. If the impact
>isn't as strong, however, the pieces of it will come back together under
>gravities powers and the various grades (3's, 4's...) will be mixed
>together. The high number of H breccias (like Zag which is an H3-6 or
>Noblesville which is an H4-6) would seem to indicate that the H parent body
>is a rubble pile asteroid. Subsequent heating in the core of the asteroid
>doesn't happen because the nuclear isotopes that caused that heating have
>most likely already ran their course by this time. This would seem to be
>backed up by the reflectance spectra of asteroid 6 Hebe which, depending on
>what area is being imaged, has areas that match the respective grades of
>H's.
>I also know there are large sections of iron in this chondrite that are
>unlike any other meteorite out there. These large sections of irons will
>display a Widmanstatten like most iron meteorites when etched. To be able
>to form the necessary bands in the pattern would require that this meteorite
>was formed deep within the asteroid so that there would be plenty of
>insulation (in the form of rock) to keep the heat in the inside of the
>asteroid so that the kamacite and taenite would have the needed time to grow
>large enough to show up when etched. Something that's interesting about the
>nickel-iron in Portales is that the metal in the veins of this meteorite is
>different from the metal flecks seen in all chondrites (especially the H's).
>Another unusual thing is that there is less free iron in the silicate areas
>of Portales than in normal H chondrites (about 4% in comparison to the
>normal 15%-19%) even though fayalite values remain pretty much the same as
>other H's (19.3% +/-0.4%). Check out the Met. Bul. containing information
>on this meteorite at
>http://www.uark.edu/campus-resources/metsoc/metbull/mb83.htm
>SOOOOOOOO, to get to the point of this email, how do I think Portales was
>formed? Early in the H parent body's history a pretty good sized impact
>happens on the H parent body. Its powerful enough to disrupt the asteroid
>to its center but not necessarily powerful enough to break up the asteroid.
>When it does this, some of the free metal in this region pools together to
>form the large metal veins. Keep in mind, this is early enough in its
>history that the nuclear isotopes that are heating this asteroid are still
>active. Also, since Portales Valley is an H6 that would mean that is
>towards the core of the asteroid and has plenty insulation in the rocks
>above it to keep it warm enough to sustain the kamacite and taenite growth
>needed to form the Widmanstatten patterns that are seen in the large metal
>areas of Portales Valley.
>My 8 cents,
>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 harlan
>trammell
>Sent: Wednesday, June 05, 2002 11:40 AM
>To: meteorite-list_at_meteoritecentral.com
>Subject: [meteorite-list] portales
>
>
>how do YOU think portales got formed?
>
>
>
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Received on Wed 05 Jun 2002 04:40:54 PM PDT