[meteorite-list] What is more important in classification?

[Michel FRANCO]

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-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] De la part de Carl Agee
Envoyé : lundi 6 janvier 2014 18:10
À : Jim Wooddell
Cc : meteorite-list at 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: agee at unm.edu
http://meteorite.unm.edu/people/carl_agee/



On Mon, Jan 6, 2014 at 8:57 AM, Jim Wooddell <jim.wooddell at 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 technology....maybe 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.wooddell at suddenlink.net
> http://pages.suddenlink.net/chondrule/
>
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