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MES etch patterns (revisited)

http://home1.gte.net/bverish/vaca13.jpg
http://home1.gte.net/bverish/vaca19.jpg
http://home1.gte.net/bverish/vaca20.jpg

On 9/9/98, Mike Farmer wrote:

>  
> Hello list members,
> ----SNIP!------
> I also wonder if anyone has some ideas of how this formed, after you look at these brecciated pieces of stone immersed in metal! This meteorite is truly an enigma and I think it will take a long time for the scientists to unlock it's secrets.
> -----SNIP!-------
> 
> Click here to go see what I mean!
> http://www.theskyisfalling.com/portales/index.html
> 
> Mike Farmer
> 

Back in April, I made the following post to this List.  I had produced a
(microscopic) etch pattern in a specimen of Vaca Muerta that I had
purchased from Michael.  Back then, I posed several questions regarding
what sort of cooling rates were necessary for Fe-Ni to form a micro
Widmanstatten pattern after two meteoroids had collided.  I resubmit
this question for comments/opinions.

My original post was brought to mind, after I read the follwing quote
which comes from darryl pitt's Portales Valley Meteorite web page
(referenced by Farmer):
> "Scientists originally thought PV to be a mesosiderite. It was then widely thought to be an H6 impact melt. However, the iron contained within impact melts does not etch...and the iron in PV etches."
>

Let me end with this - not knowing that "impact melt [iron] does not
etch" I naively etched my Vaca Muerta specimen with the assumption that
all alloys must etch!

My original post follows:

> From - Wed Apr 29 14:21:35 1998
> Message-ID: <354799DF.53D1@tripod.net>
>
> Date: Wed, 29 Apr 1998 14:21:35 -0700
> From: Bolidechaser 
> To: meteorite-list@meteoritecentral.com
> CC: bolidechaser@tripod.net
> Subject: Etch Pattern in Vaca Muerta
> 
> Hello List members,
> 
> Recently I obtained a 4gm specimen of Vaca Muerta.  I know I'll get my
> hand slapped for this, but after polishing the cut side, I couldn't
> resist the urge to etch the mostly metallic surface.  Lo and behold,
> what had formed was a microscopic etch (Widmanstatten?) pattern!
> (see attachments)
> Questions:
> Can anything be inferred from this very fine pattern regarding metallic
> nickel concentration (ataxites?), or does that not apply to
> stony-irons(mesosiderites)? 
> 
> Were an iron meteoroid to remelt, say by impact with another meteoroid,
> wouldn't the resolidified metal have a finer crystal pattern, more as a
> result of a comparatively quicker rate of solidification and less as a
> result of Fe-Ni composition?  Would there be a pattern at all?
> 
> Could etch pattern types in stony-irons be diagnostic for determining
> mantle-derived versus impact-derived parent melt?
> 
> Hoping my questions make some sense, 
> Bob Verish
> 
> --
> 
> --------------4C3F81E6812
> Content-Type: image/jpeg; name="vaca13.jpg"
> Content-Transfer-Encoding: base64
> Content-Disposition: inline; filename="vaca13.jpg"
> 
> /

-- 
http://home1.gte.net/bverish/vaca13.jpg
http://home1.gte.net/bverish/vaca19.jpg
http://home1.gte.net/bverish/vaca20.jpg
--
*****************************
"How can you benefit humanity, if humanity has not a clue to 
what (meteoritics is) doing for them? It is a point that will never be
explained.!" - F. Stroike
*****************************

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