[meteorite-list] Petrologic Groups

From: Frank Cressy <fcressy_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:08 2004
Message-ID: <001101c092eb$f2be1fd0$4033ff3f_at_g10fb>

Hello Rob's and list,

> Can or would anyone on the list take a moment and explain to me the 1-10
> subgrouping system on the petrologic group 3's?

Petrographic grades 3.0 through 3.9 are obtained by measuring changes of
thermoluminescence (TL) of chondrules. TL measures the luminesence of the
sample after it is irradiated.
During mild metamorphism tiny grains of feldspar start to grow in a glassy
chondrule. The higher the metamorphism, the more feldspar is present and
feldspar causes a marked increase in thermoluminence. This allows one to
subdivide the petrographic grade 3 meteorites.
Hope this helps.
Regards,
Frank







Also, could someone please explain how a chondrite achieves a petrologic
> classification with a range (ie H3-5 or L3-6)?
>
> And question number 3... Is it typically, or even consistently possible,
> with visual examination alone, to distinguish a Carbonaceous Chondrite
from
> an L or H class Chondrite? An LL from and L class? Or an Enstatite from
a
> more common H (or L) class?
>
> Thank you so much for taking time to help me with these questions.
> -Robert Beauford : )
>
>
>
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Received on Fri 09 Feb 2001 05:59:22 PM PST