[meteorite-list] Geophysics, meteorites, and Electron microscopy-QUESTION
From: Shawn Alan <photophlow_at_meteoritecentral.com>
Date: Thu, 8 Sep 2011 15:54:22 -0700 (PDT) Message-ID: <1315522462.35183.YahooMailClassic_at_web160103.mail.bf1.yahoo.com> Carl and Anne and Listers. Carl thank you for your explanation on SEM analysis. As for testing meteorites I assume they have to be a thin slice from what I had read. Now are there other tests where you can take 30mg of the meteorite and get the same result? But I would assume this would be destructive process because the fragment might have to be crushed up into power form. If this is the case, what equipment would be involved or process and is it more feasible to have the specimen in a thin section form. Why I ask is that some meteorites are super rare, and in order to have a SEM test, one must have a thin slice and from my understanding that takes about a gram or so of the meteorite in order for that to happen. Not good for the meteorite nor for the collection it comes from if its rare. As for the electron microscopy I asked Santa for one and also a scientist. I hope I have been good enough this year to get one in my stocking. Shawn Alan IMCA 1633 eBaystore http://shop.ebay.com/photophlow/m.html [meteorite-list] Geophysics, meteorites, and Electron microscopy-QUESTIONCarl Agee agee at unm.edu Thu Sep 8 09:36:36 EDT 2011 Previous message: [meteorite-list] Geophysics, meteorites, and Electron microscopy-QUESTION Next message: [meteorite-list] Ad and new website announcement Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] Hi Shawn, It's actually the electron microprobe that gives the quantitative analyses needed for classification of stony meteorites. The data is usually output in tables of oxide component concentrations in weight percent, totalling hopefully, to approximately 100%. The microprobe software lets you select which elements (expressed as oxides) to analyze and assign the element to one of the probe's spectrometers. The software will also give atomic concentrations to check for mineral stoichiometry. For metals and sulfides the output is usually in element percent. Calibration of the probe against known standards (minerals or compounds similar to what are in your meteorite) precedes the microprobe session and can take several hours. Once the probe is calibrated, you are good to go on your first unknown meteorite that would normally be in a polished thin section or polished epoxy-cast probe mount. Because the calibration is time consuming it is economical to do several samples in a single session. Sessions can go on for hours, and you can even set up a collection of x-y coordinates and let the auto-feature of the probe analyze different spots all night long. In the morning a stack of data would be be waiting for your perusal and evaluation. Of course there are other tests and analyses that contribute to a high quality meteorite classification, which include visual textural information from both polarizing microscope and SEM observation (e.g. shock effects, percent mineral make-up, weathering), and of course macroscopic characteristics seen in the hand sample. Oxygen isotopes are also great to have, especially as a "court of appeals" for borderline cases or for anomalous meteorites that don't fall into clear-cut geochemical groups. There are many other techniques such as isotopic age dating, cosmic ray exposure, bulk trace element analyses, and so on that enhance the characterization of a stony meteorite, but the electron microprobe is the work horse for most classification data. Someone who has done work on Ensisheim (LL6) and Saint-S?verin (LL6) could give a better answer that I can about the their subtle differences and whether the microprobe can distinguish between them, but my guess would be yes, especially when combined with SEM imaging. The length of time for classification from start to finish, including the write-up is variable. The initial ID or categorization of an unknown doesn't have to take long, that's what emerges in the first hour or so of microprobe analysis. But often, for a water-tight, authoritative classification, a second probe session may be required. Plus a lot of the time is spent puuzzling through the data and narrowing down the possibilities. It's like detective work, and personally I find it immensely engaging. Hope this helps, Carl Agee -- 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: agee at unm.edu http://epswww.unm.edu/iom/pers/agee.html ----------------------------------------------------------------------------------------------------------------------------------------------------- On Wed, Sep 7, 2011 at 4:47 PM, Shawn Alan <photophlow at yahoo.com> wrote: > Hello Carl and Listers > > Great post on scanning electron microscope (SEM) process, now does this process also ID the whole classification of the meteorite which is used for classifying meteorite for the Meteoritcal Bulletin database? I know alot of school are discontinuing classifying meteorites is UNM also doing the same? > > Question if someone wanted this service to be done on a meteorite, how much would it cost, cause these days money talks and helps everyone out when it comes to classifying meteorites or confirming that the meteorite is the meteorite suggested to be. Also can this process determine the difference between Ensisheim (LL6) and Saint-S?verin (LL6) by the cosmic ray exposure or terrestrial age. These two meteorites look identical and some can fake it. Does SEM also cover that test or is that a different test? Lastly how long does it take for you to classify a new meteorite from start to finish if its a stony meteorite? > > > Shawn Alan > IMCA 1633 > eBaystore > http://shop.ebay.com/photophlow/m.html > > > > > [meteorite-list] Geophysics, meteorites, and Electron microscopyCarl Agee agee at unm.edu > Tue Sep 6 12:27:18 EDT 2011 > > > Previous message: [meteorite-list] Geophysics, meteorites, and Electron microscopy > Next message: [meteorite-list] FW: High Noon! > Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] > > A scanning electron microscope (SEM) is great for high magnification > images that also contain information about the chemical composition of > the different minerals in meteorites. SEM is also a quick way to do a > qualitative analysis of a sample, say for example, detecting nickel in > iron meteorites with energy dispersive spectroscopy (EDS). > > My instrument of choice for definitive ID of stony meteorites is the > electron microprobe. This also has SEM imaging capability. In less the > hour, on a calibrated electron microprobe, I can make a definitive ID, > although unequilbrated chondrites can take more time to narrow down > the possibilities. Some of the key geochemical quantities that help in > categorizing are, Fe/Mn of olivines and pyroxenes, the fayalite and > ferrosilite content of the olivines and pyroxenes, the > anorthite-albite content of plagioclse, and a few other parameters, > plus the percent mineralogy and other textural characteristics. > > So for a simple example lunar olivines usually have higher Fe/Mn than > terrestrial basalt olivines. Check out this page's second figure for > an overview of Fe/Mn versus plagioclase content of planetary basalts: > http://www.imca.cc/mars/martian-meteorites.htm > > Carl Agee > > -- > 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: agee at unm.edu > http://epswww.unm.edu/iom/pers/agee.html > > --------------------------------l---------------------------------------------- > Geophysics, meteorites, and Electron microscopy > > Barb and Jake Baker bakers5acres at frontiernet.net > Tue Sep 6 10:50:46 EDT 2011 > > Previous message: [meteorite-list] [AD] Canyon Diablo 2,7 kg. CHEAP! > Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] > > ________________________________ > Could someone tell me, in Microscopy 101 language: How is an electron > microscope used in the study of meteorites? Using electron microscopy - > what differences are apparent between meteorites and terrestrial rocks? For > instance what are the microscopy differences between lunar basalt and > terrestrial basalt? > > Thanks > > > > > > Previous message: [meteorite-list] Geophysics, meteorites, and Electron microscopy > Next message: [meteorite-list] FW: High Noon! > Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] > > More information about the Meteorite-list mailing list > > Previous message: [meteorite-list] Geophysics, meteorites, and Electron microscopy-QUESTION Next message: [meteorite-list] Ad and new website announcement Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] More information about the Meteorite-list mailing listReceived on Thu 08 Sep 2011 06:54:22 PM PDT |
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