Re: [meteorite-list] What is more important in classification?
Hi Jim, The electron microprobe is the workhorse for classifications, and most of this can be done simply with a probe mount (epoxy mounted sample that has been polished). In general you don't need a thin section or a petrographic microscope, although I always use a reflected light petrographic microscope for reconnaissance of the probe mount before it goes on the electron probe. The electron microprobe produces quantitative data that is usually necessary for detailed, high quality classification of chondrites and achondrites. For example the chemical compositions of fine grained olivines, pyroxenes, feldspars, etc. (which are diagnostic for classification) can really only be done with high precision by the electron microprobe. On the other hand, a polished thin section is nice because it can be both microprobed and be used for optical examination. There are some useful things you can do with transmitted light microscopy, such as describe shock effects and weathering and other optical subtleties that will not be easy to see with backscatter electrons. A lot of this type of detail though is not really needed for a classification. It gets into the realm of a research project, where you might also want TEM or age dating or cosmic ray exposure and so on -- the list of instruments is very long... Thin sections are more work to make than probe mounts. For iron meteorites usually a probe mount is all you need, because all you will be doing is looking at or analyzing the surface. And for irons, bulk chemical analyses are usually done for classification, which is not usually the case for chondrites and achondrites -- although for lunars INAA is great for grouping the breccias. Carl * Carl B. Agee Director and Curator, Institute of Meteoritics Professor, Earth and Planetary Sciences MSC03 2050 University of New Mexico Albuquerque NM 87131-1126 Tel: (505) 750-7172 Fax: (505) 277-3577 Email: a...@unm.edu http://meteorite.unm.edu/people/carl_agee/ On Mon, Jan 6, 2014 at 8:57 AM, Jim Wooddell jim.woodd...@suddenlink.net wrote: Hi all! Just a few general questions... The involves a mount and a thin section. What is more important now-a-days in classification? This mainly revolves some questions I have that I am not sure how to ask...mainly to those that classify. If you have a million dollar Scanning Election Microscope and can probe around and can determine classification from the geochem and BSE images, how important is it to see the transmitted and reflected features in a petrographic microscope? I suppose my thoughts and questions are possibly in reference to new technology vs. old technologymaybe not...but close and really deeper than just yes and no answers. Not that SEM's are new technology...just saying. I was told a while back you can not classify without both. So Why??? Are the SEM's not capable of doing what a petrographic microscope can do? Thanks! Jim -- Jim Wooddell jim.woodd...@suddenlink.net http://pages.suddenlink.net/chondrule/ __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] What is more important in classification?
I always want a doubly-polished thin section to do classification of stony meteorites. To determine the petrologic type of a chondrite, it is useful to gauge the degree of recrystallization (best done in transmitted light) and look for the size of plagioclase grains (which can be done in an SEM, BSE mode of an electron microprobe, and in reflected light, since plagioclase is a darker gray than olivine or pyroxene). To assess the degree of weathering, reflected light is most useful. The probe, of course, will give you the olivine, pyroxene, plagioclase, kamacite, etc. compositions. But in general, in order to get a feel for a stony meteorite (in terms of shock, brecciation, recrystallization, abundance of matrix material, etc.), I want to be able to use the probe and see the rock in transmitted and reflected light. I can also then probe interesting features that reveal themselves with the petrographic microscope. I don't worry so much about the fuzzy line between classification and research. Alan Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html - Original Message - From: Jim Wooddell jim.woodd...@suddenlink.net To: meteorite-list@meteoritecentral.com Sent: Monday, January 06, 2014 7:57 AM Subject: [meteorite-list] What is more important in classification? Hi all! Just a few general questions... The involves a mount and a thin section. What is more important now-a-days in classification? This mainly revolves some questions I have that I am not sure how to ask...mainly to those that classify. If you have a million dollar Scanning Election Microscope and can probe around and can determine classification from the geochem and BSE images, how important is it to see the transmitted and reflected features in a petrographic microscope? I suppose my thoughts and questions are possibly in reference to new technology vs. old technologymaybe not...but close and really deeper than just yes and no answers. Not that SEM's are new technology...just saying. I was told a while back you can not classify without both. So Why??? Are the SEM's not capable of doing what a petrographic microscope can do? Thanks! Jim -- Jim Wooddell jim.woodd...@suddenlink.net http://pages.suddenlink.net/chondrule/ __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] What is more important in classification?
Hi all, Thanks Carl for the clearest explanations ever engraved about meteorite analysis, to be etched on all web sites. Regards Michel IMCA 3869 -Message d'origine- De : meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list-boun...@meteoritecentral.com] De la part de Carl Agee Envoyé : lundi 6 janvier 2014 18:10 À : Jim Wooddell Cc : meteorite-list@meteoritecentral.com Objet : Re: [meteorite-list] What is more important in classification? Hi Jim, The electron microprobe is the workhorse for classifications, and most of this can be done simply with a probe mount (epoxy mounted sample that has been polished). In general you don't need a thin section or a petrographic microscope, although I always use a reflected light petrographic microscope for reconnaissance of the probe mount before it goes on the electron probe. The electron microprobe produces quantitative data that is usually necessary for detailed, high quality classification of chondrites and achondrites. For example the chemical compositions of fine grained olivines, pyroxenes, feldspars, etc. (which are diagnostic for classification) can really only be done with high precision by the electron microprobe. On the other hand, a polished thin section is nice because it can be both microprobed and be used for optical examination. There are some useful things you can do with transmitted light microscopy, such as describe shock effects and weathering and other optical subtleties that will not be easy to see with backscatter electrons. A lot of this type of detail though is not really needed for a classification. It gets into the realm of a research project, where you might also want TEM or age dating or cosmic ray exposure and so on -- the list of instruments is very long... Thin sections are more work to make than probe mounts. For iron meteorites usually a probe mount is all you need, because all you will be doing is looking at or analyzing the surface. And for irons, bulk chemical analyses are usually done for classification, which is not usually the case for chondrites and achondrites -- although for lunars INAA is great for grouping the breccias. Carl * Carl B. Agee Director and Curator, Institute of Meteoritics Professor, Earth and Planetary Sciences MSC03 2050 University of New Mexico Albuquerque NM 87131-1126 Tel: (505) 750-7172 Fax: (505) 277-3577 Email: a...@unm.edu http://meteorite.unm.edu/people/carl_agee/ On Mon, Jan 6, 2014 at 8:57 AM, Jim Wooddell jim.woodd...@suddenlink.net wrote: Hi all! Just a few general questions... The involves a mount and a thin section. What is more important now-a-days in classification? This mainly revolves some questions I have that I am not sure how to ask...mainly to those that classify. If you have a million dollar Scanning Election Microscope and can probe around and can determine classification from the geochem and BSE images, how important is it to see the transmitted and reflected features in a petrographic microscope? I suppose my thoughts and questions are possibly in reference to new technology vs. old technologymaybe not...but close and really deeper than just yes and no answers. Not that SEM's are new technology...just saying. I was told a while back you can not classify without both. So Why??? Are the SEM's not capable of doing what a petrographic microscope can do? Thanks! Jim -- Jim Wooddell jim.woodd...@suddenlink.net http://pages.suddenlink.net/chondrule/ __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] What is more important in classification?
Hello Melinda, Alan and Carl, Thank you all very much for these explanations and the learning opportunity. You folks are great! I suppose I over worry about things when one person orders a mount and another a mount and thin section and another just a thin section. Sometimes a returned mount is not possible simply because there was not enough material left on the final mount cut. So, I began to think why a TS would really be needed with my total lack of experience on an SEM. I now have a better understanding about the mounts and thin sections I am making. I did not consider the possibility of further research in regards to the thin sections in my thoughts and you all brought that into the light for me as well. Thank you! Jim -- Jim Wooddell jim.woodd...@suddenlink.net http://pages.suddenlink.net/chondrule/ __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
