[meteorite-list] Carancas meteorite...glassy spheres.

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 6 Oct 2007 19:17:43 -0500
Message-ID: <117701c80877$805677e0$b92ee146_at_ATARIENGINE>

Hi, Graham, List,

    Yeah, I mentioned the glassy spheroids in my
first 1 or 2 posts. They can form from the ablative
trail or from impact.

    IF an impactor vaporizes, or any substantial part
of it, a cloud of rock vapor is ejected by the shock
front of its own formation. Rapidly cooled by the
surrounding atmosphere, the tiny condensing droplets
of molten rock solidify. Because they are quenched
rapidly (if not "instantly"), no crystallization of the
mineral can take place -- you get amorphic "glass."

    Because of the heat of vaporization, they possess
no magnetic properties whatever; they're just tiny beads
of glass. However, they maintain the bulk composition
of the meteorite (minus the volatiles); if you find any,
it can determined if they're from the meteorite or not
this means.

    The "meteorite dust" should contain some spheroids
from ablation, which produces not only molten rock
stripped from the meteoroid but a fraction that actually
vaporizes in the ablative process. Finding small qualtities
right up the crater would indicate the impactor ablated
all the way to the ground (it's been observed, though
rarely). That would set the minimum impact velocity at
about 2000 meters per second.

    Finding a larger amount of spheroids distributed
though the ejecta blanket and possibly further afield
would mean the impactor or part of it vaporized on
impact. Vaporization by impact requires a high specific
energy, about 18,000 joules per gram of rock, which
is the kinetic energy of an impact at 6000 meters per
second.


Sterling K. Webb
----------------------------------------------------------
----- Original Message -----
From: "ensoramanda" <ensoramanda at ntlworld.com>
To: <Meteorite-list at meteoritecentral.com>
Sent: Saturday, October 06, 2007 6:12 PM
Subject: Re: [meteorite-list] Carancas meteorite...glassy spheres.


Hi,

In earlier discussions on the list it was discussed...I think!...that if
the Carancas meteorite was still ablating near to impact that there
would be evidence in the form of ablation material around the site. The
dealer in Bolivia informed me that there were indeed small glassy
spheres around in the soil found by locals with magnets. Unfortunately
he did not collect or record any.

Or could these be formed by heat on impact?

Anybody have any thoughts.

Mike, Moritz or Rob. Did you come across any?

Graham Ensor


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Received on Sat 06 Oct 2007 08:17:43 PM PDT