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

[Carl Agee]

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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