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

[Notkin]

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.