[meteorite-list] Re: Sikhote Question, Impact Pits, Oriented Campo

From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Sat Nov 5 21:34:00 2005
Message-ID: <005e01c5e27a$905cb750$dd578b90_at_mandin4f89ypwu>

G'day Geoff and all,

I have found this to be a particularly interesting subject over the past
couple of years after I purchased a fascinating 32.8g individual and as more
of these specimens have come to light. I too arrived at a similar conclusion
to yourself.

http://www.meteorites.com.au/features/funkysa.html

I don't necessarily agree with the theory that these features were created
by in falling pieces on the ground as the size of the impactors required for
a small impact pit (~<20mm) would have reached terminal velocity WAY before
they reached the ground. I believed that they were created when the SA main
body was detonating during flight and at that point would have been spraying
small pieces everywhere like bullets. I guess this theory may also extend to
large individuals exploding and spraying small pieces on the ground around
craters.

However, I found that about 90%+ of all the SA's I've seen showing this
feature are oriented in some form with the pit on (or around) the trailing
edge. This makes me think the mid-air theory slightly more likely. I was
talking with someone who does ballistic calculations on what the figures for
an iron-iron impact pit would be but they never got back to me. Maybe
someone on this list can do the calculations or know someone that could?

Just my thoughts,

Jeff Kuyken
I.M.C.A. #3085
www.meteorites.com.au



----- Original Message -----
From: Notkin
To: Meteorite List
Sent: Sunday, November 06, 2005 1:12 PM
Subject: [meteorite-list] Re: Sikhote Question, Impact Pits, Oriented Campo


Dear Jim, Matt, and Listees:

Jim, I enjoyed your good photo of that very unusual Sikhote, thanks,
and was interested in Matt's explanation.

Nice coincidence, as when you posted that I was about to photograph an
usual Sikhote-Alin of my own.

When I started collecting Sikhotes seven or eight years ago, I was
under the impression that all individuals had come through the
atmosphere on their own, and all shrapnel pieces were the result of
explosive fragmentation around the craters (this view supported, I
believe, by the fact that only shrapnel is found in the craters?). Over
time, I've seen a few pieces that exhibit characteristics of both
individuals *and* shrapnel, and I'm sure some of you have too. An
example would be, say, a ~1kg otherwise completely regmaglypted
individual that has one sheared, shrapnel-like face. I expect this is
the result of a larger individual fragmenting in the air shortly before
impact.

Now I've come across something really interesting: it appears to be a
normal shrapnel fragment, weight 266.4 grams, except it has a very
distinct impact pit and splash rim. It seems to me that an impact pit
could only have been formed during flight, meaning some "pure" shrapnel
pieces must therefore have been created by mid-air fragmentation, not
explosive fragmentation upon impact. Could such fragmentation be the
result of mid-air collisions, or breaking up along planes as a result
of atmospheric pressure?

Have a look:

http://www.aerolite.org/gallery/sikhote-alin-266-4.htm


Of course, this is probably all explained in Krinov's lovely little
book about Sikhote-Alin, but my Russian isn't up to it I'm afraid : )

Any comments, theories, or explanations welcomed.


And for those of you who -- like me -- dig impact pits, I have a lovely
little Sikhote with TWO impact pits closing on Ebay tomorrow, and a
gorgeous oriented regmaglypted Campo closing tonight in an hour. It's
at 12 cents per gram now! A real bargain for someone.

Here they are:

http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZpsiloceras


Best to all from Tucson,

Geoff N.

______________________________________________
Meteorite-list mailing list
Meteorite-list_at_meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Sat 05 Nov 2005 09:34:04 PM PST