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Re: MES etch patterns (revisited)
To add another spin to Darryl's statement, it is theorized that Ni-poor ataxites
are "cooked" hexahedrites and octahedrites, probably from an impact with another
body. In effect, this gives the ataxites a pattern, albeit distorted. For example
take a look at Guffey, Colorado, or Carver, Alabama iron meteorites. I would not
rule out Portales as an anolmalous mesosiderite formed by impact, in fact, I think
that is what the metal-rich portions are. The stone portions within the metal-rich
variety could have at one time been a 3-type chondrite, but after impact with the
metal-rich body, they have been metamorphosed to a 6 end-member. Looking at my
piece, I do see shock veins of metal running through the stone portions.
A very interesting meteorite!
Best wishes,
--
Matt Morgan
Mile High Meteorites
http://www.mhmeteorites.com
P.O.Box 151293
Lakewood, CO 80215-9293
Darryl Pitt wrote:
> 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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