[meteorite-list] Classification of Chondrites Without a Number

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Tue, 17 Aug 2010 15:46:31 -0400
Message-ID: <4C6AE717.2030707_at_usgs.gov>

Well, there are ways and there are ways...

Petrologists can estimate the subtype (3.0-3.9) using optical
microscopy, and with training this is actually pretty good for the
lowest types (3.0-3.1). Above that, it's probably no better than +/-0.3.

With data on a few dozen olivine compositions (Fe-Mg-Si data), which can
be gotten using any polished section and an SEM or electron microprobe,
you can do somewhat better on subtypes above 3.4, say +-0.1-0.2. But
types 3.0-3.4 all look the same pretty much. But if you add in Cr
analyses in olivine, plus some other microprobe data, including analyses
of kamacite, you can break out all the subtypes 3.00-3.2.

You can use thermoluminescence (TL) and cathodoluminescence to get to
+/-0.1, the former requiring a powdered sample and the latter a polished
section. Raman spectroscopy data can also be used.

It's important to know what was done in order to assess how precise it
is likely to be.

Jeff

On 8/17/2010 2:56 PM, bernd.pauli at paulinet.de wrote:
> Hello Greg S., Jeff Gr. and List,
>
> Jeff wrote: "The classification was not done using a thin section"
>
> If I am not mistaken, a "simple" petrographic microscope may be good
> enough to determine if an ordinary chondrite is an L3, an LL3, an H3,
> etc. but in order to precisely determine whether a chondrite is an L3.x,
> LL3.x, an H3.x, meteoriticists will have to use SEM (scanning electron
> microscopy).
>
> Best wishes,
>
> Bernd
>
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Received on Tue 17 Aug 2010 03:46:31 PM PDT