[meteorite-list] More petrographic questions.

From: E.L. Jones <jonee_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:11 2004
Message-ID: <3A94256D.FC4ED886_at_epix.net>

Hello David,

My thoughts....

The terms chondrite and achondrite are names of categories with general--
not absolute characteristics... ( remember the "People's Republics" --
hardly lived up to their names either!) The overall chemistry and nearest
chemical neighbor governs the assignment to categories. As it is, I am
not sure that the traditional distinction... the degree of differentiation
in the parent body can hold up the more we learn... but now it seems the
best we have.

I have no problem with the use of "7" but recall that the value "1" also
means an absence of chondirites. Maybe we need to go back to the wisdom of
computer programers and use the "zero/0" value.

Elton

David Weir wrote:

> 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 Wed 21 Feb 2001 03:32:47 PM PST