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Re: MES etch patterns (revisited)



hi-

to effect the allignment of molecules that results in an etch requires a
very slow cooling rate. in the case of an impact melt, as a result of the
iron being conjoined with a stony matrix, the cooling rate is rapidly
accelerated.


best-
darryl




>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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