[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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