[meteorite-list] Re: "Round Rocks" from Osceola, Missouri Impact Site

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Sun Aug 20 04:24:30 2006
Message-ID: <BAY104-F58893E9013D0FF6C4F884F8400_at_phx.gbl>

Hi, all,

To me, they look like common river cobble.

If they are limestone, they would be relatively soft enough to have the
corners easily chipped off until ultimately shaped into the orbs.

Judging by the included aerial photo at the ebay site, there's lots of
rivers to wash them down hill, too.
The tributary system appears similar to that found in a mountainous/foothill
terrain, so lack of an energetic momentum wouldn't be an issue.

Occam's razor.
Coincidence that they are found at the impact area, and their round shape is
unrelated.

...Just the humble, skeptical opinion of an amateur with a geology interest,
and likely wrong.

I don't deny, however, that they are cool looking rocks, especially in a
package like what's for sale!

Cheers,
Pete


From: Mr EMan <mstreman53_at_yahoo.com>
To: rockhounds_at_lists.drizzle.com, metlist
<meteorite-list_at_meteoritecentral.com>
Subject: [meteorite-list] Re: "Round Rocks" from Osceola,Missouri Impact
Site
Date: Sun, 20 Aug 2006 00:42:29 -0700 (PDT)

Interesting follow up note as I Google about trying to
visualize the dynamics and avoid broaching the "T
word"--tektite. The article below speaks of them
being shale kernals which upon falling back into the
melangue over time became "chert concretions". I also
noted that one of the affected formations is the
Keokuk limestone of geode fame.


"Missouri rock balls. One of the largest meteorite
craters in the United States is in the state of
Missouri where a rock 1,200 feet in diameter plunged
into Earth's atmosphere sometime around 310 to 340
million years ago. It crashed into territory where we
find the modern towns of Weaubleau and Osceola. The
impact crater encircles the modern community of Vista,
making it one of only two U.S. communities, along with
Middlesboro, Kentucky, totally encircled by a
meteorite crater or crater remnants, according to
geologist George H. Davis, a member of the team that
used shallow core drilling to investigate the
Weaubleau-Osceola meteorite impact in July 2003.
Osceola and Weaubleau are not within the impact
crater.

Geologists say such a quarter-mile-wide meteorite
could explain how some rocks they found on the ground
had come to be folded over and other rocks containing
shattered quartz had ended up in the Ozark Mountains.

Residents of the area around Osceola have found a lot
of strange, perfectly-round rocks. Geologists theorize
the round stone balls are chert concretions. They
suggest the impact blasted up gravel-sized pieces of
shale that fell back to the ground. Silica-rich
solutions seeped in around the small shale pieces and
hardened in place. Those chert concretions are
evidence that the impact actually occurred, according
to Davis.

The folded rocks are visible in a local quarry and
Davis describes them as "fascinating." The team of
geologists theorize that the folding happened in "mere
milliseconds." Their drilling into the structure
turned up one large piece of granite that had been
lifted nearly 1200 feet vertically through rock and
sediment by the force of the impact."

Ercerpted from:
<http://www.spacetoday.org/SolSys/Earth/Meteorites/MeteoritesExplained.html>

Elton

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Received on Sun 20 Aug 2006 04:11:23 AM PDT