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Re: Vugs, vacuoles and voids

Hello Julia and List,

Vesicular basalt (lava) typically has a uniform texture riddled with
vesicles of similar size, which can range from microscopic to more than a
few centimeters in diameter.  It shows that the unmixing process --
exsolution -- occured uniformly when the magma rose towards the surface and
the pressure lessened sufficiently to permit the gases to escape from the
solution.  This typically happens near or on the surface.

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.

As an aside, some geophysicists have recently modelled the Earth's inner
core and predict that the iron-nickel is directionally aligned into columns,
a feature that is not readily apparent from examining iron-nickel
meteorites.

Steve

-----------------------------------------------
Steven Excell
Seattle, Washington USA
E-Mail: excell@concentric.net
------------------------------------------------
-----Original Message-----
From: JJSwaim 
To: meteoritelist 
Date: Friday, June 12, 1998 3:26 PM
Subject: Vugs, vacuoles and voids


>Hi Steven, Bernd and List,
>
>How can one determine (short of taking the sample to an expert), the
>difference between lithophysae (Latin for rock bubbles)  which,  if I
>understand correctly are from lava flows and have interior cavities with
>spheres that formed presumably as the temperatures dropped to a critical
>point, crystallized, the dissovled gases being driven out of the
>solution,  and something like the Albion meteorite?
>
>Further, if this sample has an iron fusion crust, what is the likelihood
>that it is a meteorite?  Anyone with any help would be appreciated.
>
>Best regards,
>Julia
>
>
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