[meteorite-list] fusion crust observation

From: Dave Harris <entropydave_at_meteoritecentral.com>
Date: Thu Apr 22 09:54:07 2004
Message-ID: <018f01c1ba2f$af14f4e0$849f0050_at_default>

Hi Elton!
Certainly the pits on Allende look like popped bubbles rather than a
structural element that has been preferentially ablated from the matrix.
I also have some Zag that also has a large amount of apparent outgassing ie
pitting. Certainly your observations re the composition of Millbillillie is
pertinent - being a basaltic would have outgassed when ejected onto the
surface of Vesta - whereas I could see that vesicular eucrites like Ibitira
coming from the explosive ejection of magma beneath the surface of the
parent body - it being the equivalent of shaking up a can of coke and
opening it up in a very cold environment - cold enough to freeze it solid
before all the gases escaped and trapping vesicles of magmatic gases.
I tend to think that the outgassing in Allende perhaps comes from adsorbed
water and hydrocarbons in the matrix.
Interesting...
dave

----- Original Message -----
From: "EL Jones" <jonee_at_epix.net>
To: "Dave Harris" <entropydave_at_ic24.net>
Cc: "metlist" <meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, February 20, 2002 4:38 PM
Subject: Re: [meteorite-list] fusion crust observation


> Greetings List, Dave,
>
> Gases? Could be a connection but not the reason there is a difference.
The
> smoothness of Millibillillie is likely accounted for by its distinctly
different
> chemistry/mineral makeup..... Eucrites have a glassy fusion crust because
they
> are more homogeneous and have already had their gases "outgased" in the
original
> melt of formation ( note Ibitria ,however, as an a vesiculated exception
.)
>
> Carbonaceous material such as Allende is more loosely consolidated and
could be
> subject to "plucking" of small grains during transit (as well as low
melting
> point material). The voids I see in the crust are irregular cavities so I
tend
> to discount them as a gas pocket-not saying that they could not be from
gas
> voids.
>
> Outgasing is a possibility if you consider that the methane in Carbs are
locked
> in by the cold, one could theorize, and that localized heating liberated
some
> aromatics and left voids in the crust. However, cutting should liberate
> existing pockets also it that were the case and I don't see those cavities
> within the sliced sections. These could also be a version of cooling
cracks
> when the fused material contracts upon cooling. Looks like we need to
look
> closer at this phenomena.
>
> So, while gas could be involved in Allende's crustal pits, it shouldn't
be the
> reason eucrites have a smoother crust.
>
> Regards,
> Elton
>
> Dave Harris wrote:
>
> > Hello listees,
> > ...bit of an obvious observation but I noticed on my Allende individual
I
> > got today (Thanks, Christian!) that the fusion crust is peppered with
tiny
> > holes whereas my Millbillillie crust is a solid (unperforated) glassy
coat.
> > I guess I know why this is ie exgassing during atmospheric entering,
butI
> > was just curious as to what EXACTLY what gases were escaping - water
vapour
> > or whatever.
> > And therefore the assumption that Millbillillie has far less 'free'
gases in
> > the matrix maybe drawn.
> > Any comments?
> >
> > very best!
> >
> > --
> > In gentle decay,
> > dave
> >
> > IMCA #0092
>
Received on Wed 20 Feb 2002 11:57:27 AM PST