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Re: Vugs, vacuoles and voids

Hello all,

After reading Steve's comments on the drusy vugs in the Albion meteorite
I thought I would challenge you with a little thought experiment I went
through after reading the Albion papers when they were published.

Steve is correct that it would be difficult to imagine gas bubbles being
able exsolve from nickel-iron under the extreme pressures encountered
within a differentiated body, but the papers by U.B. Marvin et al.
suggest that the drusy vugs are primary formations and not secondary
formations induced by heat or impact.

So, for fun, consider the following: first, what is the cause of the
extreme pressure found below the surface of a planetary-size body? (I
broadened the definition of "planetary-size" to include any body large
enough to differentiate.) Second, given the (or at least my) answer to
the first part of the experiment, what would be the pressure conditions
at or near the center of a differentiated body? My thought process may
be flawed, but it will be interesting to see if anyone reaches the
conclusion I did.

A final thought: Albion and Gibeon are both IVA irons, but it does not
follow that they are the same meteorite. It does suggest that they come
from the same parent body or the same area of a parent body depending on
which formation model you may follow. It's hard to imagine (but not
totally impossible) that a Gibeon specimen that was intentionally or
accidently identified as a new locality just happens to be the only
Gibeon specimen with drusy vugs. A lot of Gibeon has been cut and no
other specimens with vugs have been identified. You never know, though.
If you have some Gibeon, you might want to check it closely.

Gene

Steven Excell wrote:
> 
> The drusy vugs in the Albion iron (which I have only read about and have not
> seen) are said to be rare.  This would be especially true if Albion were
> indeed Gibeon.  The pressures within a iron-nickel planetoid core (Earth,
> asteroid, etc.) are sufficiently great that gases should not be able to
> exsolve.  It is hard to believe that a few bubbles could develop, much less
> survive, under such severve pressures that would form a core and otherwise
> prevent exsolution from occuring homogeneously through the specimen.   I
> think the vugs and voids are real and unique.  I would tend to think they
> are more likely to be pockets of minerals or imperfections leached out by
> subsequent chemical reactions within the core or "chemical weathering"
> (reactions from being exposed to other materials after being blasted out of
> the core by an impact).  This is only a hunch based upon what is known about
> the intense pressures and temperatures within an iron-nickel core.
>
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