[meteorite-list] monomict - genomict - polymict

From: MICHAEL TETTENBORN <tett_at_meteoritecentral.com>
Date: Fri, 1 Dec 2006 14:04:37 -0500 (EST)
Message-ID: <81024.70571.qm_at_web88208.mail.re2.yahoo.com>

Bernd,

We should also understand "cumulate". Another common
adjective when describing eucrites.

As I understand things, cumulate refers to largish
crystals "accumulating" in a pile and relatively
undisturbed. So a cumulate eucrite formed deeper
within the parent body (Vesta) where temperature were
warmer and the crust more fluid? Will check my
references later.

When I looked at various eucrite pictures I was
reminded of Millbillillie but Millbillillie is not
listed as a cumulate eucrite in the Met. Base. Could
it be one? It has a very distinct crystal pile in my
opinion.

Cheers,

Mike

--- bernd.pauli at paulinet.de wrote:

> Steve Arnold wrote:
>
> "I have seen with many eucrites that there is a
> polymict
> type and a monomict type. What are the differences?
>
>
> Geoff responded:
>
> "Dear Steve: May I recommend a very useful resource
> to you: The Cambridge Encyclopedia of Meteorites"
>
>
> Hello All,
>
> On page 344 of the glossary, we find:
>
> monomict breccia:
>
> A brecciated meteorite composed of angular
> fragments and matrix all of like composition
>
> On page 345 of the glossary, we find:
>
> polymict breccia:
> A rock made up of angular fragments or clasts
> from other rocks of different compositions
>
> On page 343 of the glossary, we find:
>
> genomict breccia:
>
> A brecciated meteorite in which the individual
> clasts are compositionally
> of the same group but have differing petrographic
> characteristics
>
> Wasson puts it this way:
>
> WASSON J.T. (1974) Meteorites Classification and
> Properties
> (Springer-Verlag, Berlin, Heidelberg, New York,
> Appendix I,
> Glossary, p. 242):
>
> Breccia:
>
> A fragmental rock type including components (the
> larger pieces called
> xenoliths or clasts) which were previously part of
> another rock. In a
> *monomict* breccia all components originated in the
> same rock; in a
> *genomict* breccia the components originated in
> distinct but genetically
> closely related rocks; in *polymict* breccias the
> components originated
> in two or more unrelated rocks.
>
> Cheers,
>
> Bernd
>
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Received on Fri 01 Dec 2006 02:04:37 PM PST