Hi folks & greetings re the pallasite Q 2 ryals worth from Qatar from the frequency of fals /vs size , it appears to me that the majority of impacts are smaller ( why should impacts elsewhere be different from our observations (appart from a million reasons )) If the majority of meteorite ejecting impacts are lighter , then the surface layer would be the most affected since pallasites inhabit the boundary region of larger bodies, their total mass/ impact cross section ,would be more limited again reducing the frequency. If the meteor generating flux is considered uniform for our solar back yard & after allowing for gravity differentiation by other planets & the sun , & allowing for the probability of recognition , size of impact for meteorite escape &,& ......does the meteorite type distribution tell us the rock distribution of the solar system ie more mass ( or impact area ) for chondrites form smaller bodies,?
puzzled & off to work now allthebest colin ----- Original Message ----- From: "Ron Baalke" <[EMAIL PROTECTED]> To: "Meteorite Mailing List" <[EMAIL PROTECTED]> Sent: Monday, May 20, 2002 11:51 PM Subject: Re: [meteorite-list] Re: Mercury Meteorite Puzzle > >>While it is still possible the parent body for the E chondrites and NWA 011 > >> may be Mercury or Venus, you can't rule out asteroids just yet either. > > > > > Both of these statements are incorrect. Both Mercury and Venus are > > differentiated bodies. Neither can be the source of "chondrites" of any > > kind. They could however the the source of various "achondrites". > > Since the planets are formed from chondritic asteroids, I don't think you can > rule them out just because the meteorite is a chondrite. > > > If people are interested in a mystery here is a big one. Pallasites are > > generally > > assumed to be from the core / mantle boundry. > > That is correct. > > >There are quite a few > > pallasites > > so their formation doesn't appear to be an unusual occurance. > > Actually, pallasites are on the rare side, particularly when you compare them to the > stony chondrites. > > >There are > > also a > > lot of irons from the core side of the boundry. > > In terms of number of falls, irons are also somewhate rare (but not > as rare as pallasites), but they are common in terms of total known weight. > > >There are however no, as in > > zero, meteorites with pallasitic type olivine crystals with out an iron > > matrix. > > Since the olivine crystals are only found in an iron matrix, that should > be your first big hint. Olivine is a common mineral in stony chondrites, though > not in crystalline form, as you noted. Since olivine is common in the stony chondrites, > then you would assume that the olivine was somehow converted to crystalline form > when it became a pallasite. > > > The mantle by volume would be larger than the core of most differentiated > > bodies. So where are the olivine meteorites? One would think they would be > > at least as abundent as the pallasites. Is the pallasite theory incorrect? > > My guess would be the olivine crytals came about when the chondrite layer interacted > with the molten iron core. Since the olivine is intermixed with the nickel-iron, that > implies that they were mixed together when the metal portion was in a hot molten form, > which futher implies the chondritic material was exposed to high temperatures and > probably some pressure as well. Due to the exposure to the high temperatures, > the olivine was converted to a crystalline form. That would explain why you only > see the olivine crystals only in pallasites, the boundary layer between the > metal core and the chondritic mantle. > > Ron Baalke > > ______________________________________________ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://www.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
