[meteorite-list] More petrographic questions.

From: Frank Prochaska <fprochas_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:08 2004
Message-ID: <NDBBICFKNKHAAEEJLDALAECHCHAA.fprochas_at_premier1.net>

Hello all,

Okay, now I'm confused on the chondrite type 6 or 7 vs. achondrite issue. I
was not aware of an achondrite with relict chondrules. My understanding
from the literature was that "chondrites" are relatively primitive
meteorites in that they had elemental abundances relatively unchanged
(disregarding volatiles of course) from the protoplanetary disk and the Sun.
Some of these don't have chondrules (CIs and type 7's for example) but the
distinction was not pressence of chondrules but the chemistry. My
understanding of achondrites was that these were no longer chemically
primitive in the above sense, but were the products on partial melting,
recrystallization, etc., of chondritic parent rocks. I don't know much
about acapulcoites, but it doesn't seem likely that the underlying chemistry
of the rock could change much if it still has relict chondrules.

Can someone point me to some citations for acapulcoites and descriptions of
achondrite classification technical details in general?

Frank Prochaska

-----Original Message-----
From: meteorite-list-admin_at_meteoritecentral.com
[mailto:meteorite-list-admin_at_meteoritecentral.com]On Behalf Of David
Weir
Sent: Saturday, February 10, 2001 11:40 PM
To: MeteorHntr_at_aol.com
Cc: meteorite-list_at_meteoritecentral.com
Subject: Re: [meteorite-list] More petrographic questions.


Hello Steve,

Is there a need to add another number higher than 6 before calling a
meteorite an achondrite? Said another way, why draw a line someplace
where the metamorphism suddenly becomes a 7? This delineation is defined
as the complete lack of chondrules? Why isn't this an achondrite? And do
we even have enough of the parent rock to say for sure that there are no
chondrules? As you mentioned, look at the achondrite (acapulcoite)
Tissemoumine with definite chondrules, or even those relict chondrules
in Monument Draw. Doesn't this blur the delineation between chondrite
and achondrite, and petrologic 6 and 7? Perhaps the classificational
terms chondrite and achondrite should be abandoned as generalized
grouping terms. I'll be waiting for some answers.

David

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Received on Sat 10 Feb 2001 01:19:16 PM PST