[meteorite-list] Questions on thin sections/quartz

[lakewind at infionline.net]

Hello Warin,
Thanks for your explanation. It brought to mind a question I've had about
certain 
meteorite thin sections I've seen for sale, one of which I recently
purchased. In 
addition to the thin section, there is a scattering of thin flakes across
the slide. Is 
this a reference material to determine the correct thickness of the
section? These 
mineral flakes look nice all by themselves under x-polarized light. Thank
you for 
your help.
Best regards,
Bob

Original Message:
-----------------
From: Warin Roger warinroger at yahoo.fr
Date: Mon, 11 Sep 2006 06:46:45 +0000 (GMT)
To: suzieandjim at yahoo.com, Meteorite-list at meteoritecentral.com
Subject: Re : [meteorite-list] Questions on olivine in meterorites.


Hi Suzanne & Jim, all,
 
A rock with olivine never contains quartz. In the presence of olivine, SiO2
produces 
pyroxenes.  Quartz has a low birefringence, as opposed to olivine. Quartz
polarizes 
in the light gray and white of the 1st order. In terrestrial rocks, it is
thus easy to 
control the thickness of the thin section: quartz cannot be coloured in
cross 
polarized light. It is thus necessary to thin the thin section to remove
any colour in 
quartz.  That's what's done for terrestrial rocks.
 
In the frequent absence of quartz in meteorites, I think another reference
is used, 
like the colour of feldspars. 
  


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