[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 |
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