[meteorite-list] monomict - genomict - polymict

[MICHAEL TETTENBORN]

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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