[meteorite-list] Acapulcoites and NWA 725 - correct
From: M come Meteorite Meteorites <mcomemeteorite2004_at_meteoritecentral.com>
Date: Fri Feb 17 01:01:04 2006 Message-ID: <20060217060101.65284.qmail_at_web26211.mail.ukl.yahoo.com> Hello NWA 1054 was very studied, and its 100% confirmed is a acapulcoite - many oldest why we have found complete chondrules into - and is paired to nWA 1052, another acapulcoite. The problem is, NWA 1052/1054 have the same matrix of NWA 1058, and this have the same problems of classification why one say its a primitive achondrite like winonaite, another say its a acapulcoite etc...all 3 examples have complete chondrules and not relitic. In only one we have found Melliniite, other 2 not....mistery.... Matteo --- "Kashuba, Ontario, California" <mary.kashuba_at_verizon.net> ha scritto: > Bernd, > > > > I don't mind at all. I think I'm with you wishing I > could lean over the > 'scope and think "Ah, yes, heat and time makes > crystals grow and chondrules > disappear. Metal migrates and other stuff does > too." And thereby progress > in an orderly way from chondrites through these > primitive achondrites. > Unfortunately, it looks like there is more to it > than that. In > Discrimination of Acapulcoites and Lodranites from > Winonaites Rumble et al. > state: > > > > Combined petrological and oxygen isotopic analyses > of five Northwest African > primitive achondrites . . . have clarified the > relationships among > acapulcoites, lodranites and winonaites. It would > not be possible to > properly classify some specimens in these groups > using their mineral > compositions alone . . . . > > > > http://www.lpi.usra.edu/meetings/metsoc2005/pdf/5138.pdf > > > > To say nothing of mere appearances. > > > > I don't know what to think about Marvin's NWA 1054 > Winonaite. Matteo points > out that NWA 1054 is an acapulcoite. Further, I > don't see the abundant 120? > triple junctions mentioned in the descriptions of > NWA 1054. To me it looks > a lot like NWA 725 (Tissemoumine). > > > > The differences I see under the microscope aren't > very subtle. Nor are they > orderly. Please see these examples. The fields of > view are all the same, > three and a half millimeters from left to right. > > > > http://www.johnkashuba.com/Ach%20Acapulcoites_and_Winonaites.html > > > > Regards, > > > > - John > > > > John Kashuba > > Ontario, California > > ----- Original Message ----- > From: <bernd.pauli_at_paulinet.de> > To: <Meteorite-list_at_meteoritecentral.com> > Sent: Thursday, February 16, 2006 11:02 AM > Subject: [meteorite-list] Acapulcoites and NWA 725 > > > >> I'm must be missing something. What could one > conclude by comparing thin > >> sections of NWA 725 and a known winonaite? I > understand that > >> distinguishing > >> among acapulcoites, lodranites and winonaites is > not a textural exercise > >> nor > >> can they be resolved by just their mineral > composition. > > > > Hello John and List, > > > > I thought other list members might also be > interested in this thread, > > so I hope you don't mind me sending this mail to > the List as well. > > > > No, you are not missing anything. Hand samples of > acapulcoites, lodranites > > and > > winonaites look pretty much the same tan color (at > least to me). Only the > > micro- > > scope will reveal their subtle textural > differences and only a thin > > section in > > polarized light will show mineralogical > differences or differences in > > grain size. > > > > Unortunately I still don't have a thin section of > an acapulcoite but the > > one pictured > > in Marvin Killgore's "Color Atlas of Meteorites in > Thin Section" on pages > > 208-211 > > (Acapulco) surely looks different than the > winonaite on pages 232-235 (NWA > > 1054). > > > > Something readily noticed is grain-size: The > grains in winonaites are > > usually smaller > > than in acapulcoites. I know, unfortunately their > grain sizes overlap as a > > comparative > > overview on p. 252 of Hutchison (Meteorites: A > Petrologic, Chemical, and > > Isotopic Syn- > > thesis ) shows. To make matters even worse: almost > all cited properties > > overlap :-( > > > > Maybe the amount of troilite in NWA 725 could help > here. According to > > Hutchison, > > acapulcoites have 3-6 vol% FeS whereas winoaites > have 1-19 %. > > > > The mineral composition of NWA 725 may also be > useful in determining > > whether it > > is a winonaite or an acapulcoite. Olivine Fo and > orthopyroxene En have > > (slightly) > > higher values in winonaites, and the same is valid > for plagioclase An. > > > > Unfortunately both acapulcoites and winonaites can > have relict chondrules, > > so this > > doesn't help either. But what may help is the fact > that winonaites are > > more depleted > > in 16-O and so plot closer to the terrestrial > fractionation line than > > acapulcoites. > > > > Well, you are right ... a thin section will not > disclose such information > > so I can > > only repeat what I already mentioned above: grain > size and visual > > appearance of thin > > sections of winonaites and acapulcoites - they > just look different to me > > and Hutchison > > also states: > > > > "The winonaites are texturally similar to > acapulcoites, but the winonaites > > contain > > coarser grains and abundant crosscutting > metal-sulfide veins." > > > > So, maybe, the grain size of NWA 725 visible under > the microscope does > > hold a clue ... > > > > > > Cheers, > > > > Bernd > > > > ______________________________________________ > > Meteorite-list mailing list > > Meteorite-list_at_meteoritecentral.com > > > http://six.pairlist.net/mailman/listinfo/meteorite-list > > > > > ______________________________________________ > Meteorite-list mailing list > Meteorite-list_at_meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > M come Meteorite - Matteo Chinellato Via Triestina 126/A - 30030 - TESSERA, VENEZIA, ITALY Email: mcomemeteorite2004_at_yahoo.it Sale Site: http://www.mcomemeteorite.it Collection Site: http://www.mcomemeteorite.info MSN Messanger: spacerocks at hotmail.com EBAY.COM:http://members.ebay.com/aboutme/mcomemeteorite/ ___________________________________ Yahoo! Mail: gratis 1GB per i messaggi e allegati da 10MB http://mail.yahoo.it Received on Fri 17 Feb 2006 01:01:01 AM PST |
StumbleUpon del.icio.us Yahoo MyWeb |