[meteorite-list] Re: [MeteoriticalBulletin] Meteoritical Bulletin: Announcement 87-5
From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 10:25:36 2004 Message-ID: <5.1.0.14.2.20030506130624.0276a450_at_gsvaresm02.er.usgs.gov> <html> The fact of the matter is that there is no standard way to classify brecciated chondrites. Most chondrites are breccias at some scale. Impact melt is present in many of them, especially shocked ordinary chondrites (like PF), in a wide array of forms ranging from clasts and pockets to veins, sheets and dikes. Some scientists might look at a particular meteorite and see an L5 chondrite with a lot of impact melt, and others see an impact melt breccia with a lot of L5 clasts (I've not seen Park Forest myself, so I have no opinion of it). It's really a matter of taste as to how the classifier describes it, and it partly depends on his/her interests. People do it both ways, and we accept it for lack of any standards. The most important thing is that there are good descriptions available in the literature so that everybody can know what a meteorite is like. It's also important that there are good, representative type specimens of heterogeneous meteorites in research collections so that there's a chance of future generations being able to understand them (and reclassify them if necessary). <br><br> jeff<br><br> At 12:40 PM 5/6/2003 -0400, MeteorHntr_at_aol.com wrote:<br><br> <blockquote type=3Dcite class=3Dcite cite><font size=3D2>Hello Jeff and List,<br><br> I just noticed in the Meteoritical Bulletin (below) that Park Forest is offically classifed as an "L5" and not as an "L5 impact melt breccia."<br><br> Can that change in the future?<br><br> By the way, 5 years later is Portales Valley still just an "Ordinary H5" or has it ever been changed? <br><br> Steve Arnold<br><br> <br><br> &nbs= p; THE METEORITICAL BULLETIN<br> &nbs= p; E-mail Announcement 87-5, May 6, 2003<br> &nbs= p; <br> Park Forest 41=B029'05" N, 87=B040'45" W<br> Cook County, Illinois, USA<br> Fell 2003 March 26, approx. 23:50 hrs<br> Ordinary chondrite (L5)<br> A bright fireball was seen by numerous observers in parts of <br> Illinois, Indiana, Wisconsin and Ohio around midnight of March 26, <br> 2003. Numerous stones fell, mostly concentrated in the area of the <br> village of Park Forest. At least two houses in Park Forest were <br> struck, as was the Fire Station. Dozens of other stones or fragments <br> of stones were recovered in the area in the hours and days following <br> the fall. Total mass recovered is more than 18 kg, largest stone ~ 3 <br> kg in possession of finder. Description and classification (S. Simon, <br> UChi; M. Wadwha, FMNH; P. Sipiera, PSF): Most stones are partly to <br> fully fusion crusted. Some broken faces show brecciated texture, <br> angular clasts. Cross-cutting dark veins and dark pockets may be of=20 <br> impact melt origin. No visible chondrules in hand sample. Abundant <br> troilite and metal visible in some broken faces. Chondrules and <br> maskelynite are visible in thin section. Classified as an L5 <br> chondrite: mean olivine composition Fa24.7, mean low-Ca pyroxene <br> Fs20.7Wo1.6. Shock stage S5. Specimens: type specimen 545g (hit fire <br> station), FMNH. Other stones at FMNH: 1200g, 529g, 183g, 159g, 125g.</blockquote> <x-sigsep><p></x-sigsep> Dr. Jeffrey N. Grossman<br> Chair, Meteorite Nomenclature Committee (Meteoritical Society)<br> US Geological Survey <br> 954 National Center<br> Reston, VA 20192, USA<br> Phone: (703) 648-6184 fax: (703) 648-6383<br><br> </font></html> Received on Tue 06 May 2003 01:27:46 PM PDT |
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