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FW: Vugs, vacuoles and voids

Hello Gene and List,

The widmanstatten pattern would also remain undisturbed if an inclusion leached out or reacted with the metals after formation.  This possibility should leave some chemical traces if the reactions were with the confining metals.

However, I think the boiling sulfur is probably the best (and simplest) explanation for both the vugs and the missing sulfur.

The ability of the boiling sulfur to displace the metal in a core is still problematic.  The metal would have to be very plastic or melted liquid and unconfined enough to permit movement by the building gas pressures.  These conditions could exist but would not be the stereotypical conditions imagined for a mature, solid core except perhaps during it's initial formation during differentiation.  In this latter case, Marvin might be right on the money because "primary formation" would be very "primary."

Steve

********************************
Steven Excell
Seattle, WA 98101-1839
E-Mail: excell@concentric.net
********************************


-----Original Message-----
From:	Gene Roberts [SMTP:eroberts@ntplx.net]
Sent:	Monday, June 15, 1998 9:10 PM
To:	Met List
Subject:	Re: Vugs, vacuoles and voids

Hello Steve and list,

Sorry I missed your second post before I responded to your first --
could have avoided duplicating the answer. In response to your next
question about whether or not the gas could exert enough pressure to
create the vugs, I believe it could. Ursala Marvin's description of
Albion shows the Widmanstatten pattern is undistorted by the vugs and
may be one her reasons for considering the vugs to be primary
formations.

A common element with an affinity for iron is sulfur and it would have
been carried into the core along with the iron. Sulfur has a boiling
point of 444.6C (at 1 atmosphere). Iron has a melting point of 1535C and
a boiling point of 2750C. Since iron would be a liquid at roughly 3 1/2
to 6 times the boiling point of sulfur, there could be a significant
amount of pressure exerted on the iron. If sulfur "bubbles" did form in
the liquid iron, it would occur at temperatures well above those of 500C
to 700C where the Widmanstatten pattern forms as the iron cools and
solidifies. The Widmanstatten pattern would have formed around vugs
already present and be consistent with the noted lack of distortion.

As the temperature cooled below 444.6C, the sulfur would have condensed.
This description of the vugs from one of the Albion papers may account
for what happened to the sulfur: "The spheroidal masses consist mainly
of irregular kamacite grains. 1-35 (micrometers) across, containing
2-3.5 wt% Ni, plus a few rounded segregations of Ni-rich tetrataenite
with 55.6 wt% Ni. Enmeshed in both metals are thin, branching films of
troilite that appears to have invaded and corroded them. Scattered
throughout the spheroids are blocky, euhedral grains of daubreelite
(FeCr2S4), and scarcer ones of euhedral schreibersite
[(Ni0.54Fe0.46)3P]." Troilite (FeS) and daubreelite are both sulfur
containing minerals and may have formed as the gaseous sulfur condensed.

That got a little long-winded and I'm sure over simplified, but, yes, I
think there would be enough pressure to form the vugs. My reasoning may
be full of holes (sorry), but the vugs exist -- they formed somehow.

Steven Excell wrote:
> 
> I was joking in my previous post because Gene does have a point here and I
> thought everyone knew exactly what he was referring to.  A couple of e-mails
> to me since then convinced me that a more serious explanation is in order.
> Gravity causes pressure.  If there were a cave in the very center of the
> Earth, there would be no gravity in the cave.  It would be a "zero gravity"
> environment like a space ship.  A visitor to the cave would be weightless.
> Why?  Because there would be equal amounts of mass above, below and all
> around you.  So a void near the center of planetary core might permit gas to
> exsolve into it, but could the gas create enough pressure to push away solid
> material in order to create the void in the first place?  Mmmmm.
> 
> Does the price of Albion go up because it might be the dead-center of a
> shattered asteroid?

I'll leave that one to Steve A., Michael and Darryl.

Gene