[meteorite-list] What is and isn't a Widmanstatten Pattern was Cooling rates

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Sun, 6 Sep 2009 12:17:42 -0700 (PDT)
Message-ID: <492917.339.qm_at_web55202.mail.re4.yahoo.com>

We had a metallurgist on the list a few years back that insisted Widmanstatten patterns were found everywhere and posted some micrographs supporting his assertion. As I recall he got very ill with us when we pointed out why, what he had photos of, weren't Widmanstatten patterns. It was focused on a physical "casual" similarity not "causal" chemistry.

Once again Widmanstatten patterns aren't stress fractures nor alloy specific patterns. I further assert that metal in meteorites is NOT an alloy in that the nickel is in a specific locus within a molecule. It is therefore not a mixture but a compound, chemically speaking.

Widmanstatten patterns are a cross-sectional view of crystal latices that result from the migration of nickel atoms over eons into two distinct unusual, zoned, crystalline arrangements. Bandwidth is actually plate thickness. The migration is chemically driven while the metal is molten and only occurs in a specific range of temperatures. This is a subtle but distinct difference. This migration may even be a molecule by molecule transfer of nickel atoms which takes millions of years to clear out a 3mm band. This is to say a nickel atom may move in one side of a molecule and forces the central nickel atom to the face and lacking stability is ejected out the other side--maybe not, as the actual displacement/sorting is still an enigma. The nickel iron content may assemble from a single form as it accretes and represent a move to homogeneity interupted when the mass ran out of thermal energy. It may all start out as taenite and part of it converts to
 kamacite or vice versa. Who really knows?

I fully believe collisions would impede if not stop the process-- not speed it up. It is easy and natural to try to infer a similar pattern might be from a similar process but the only similarity is in low contrast photographs when the scale is ignored.

Elton

--- On Sun, 9/6/09, E.P. Grondine <epgrondine at yahoo.com> wrote:

> From: E.P. Grondine <epgrondine at yahoo.com>
> Subject: Re: [meteorite-list] Cooling rates
> To: meteorite-list at meteoritecentral.com, "Steve Dunklee" <sdunklee72520 at yahoo.com>
> Date: Sunday, September 6, 2009, 1:47 PM
> Hi Steve, all -
>
> I don't think they're due to repeated collisions.
>
> Suppose that we have molten iron/nickle under incredible
> compression, which is then almost instantaneously released.

> 250 parent bodies seems like a lot. Perhaps instead there
> was more differentiation within fewer parent bodies.
>
> Ed
Received on Sun 06 Sep 2009 03:17:42 PM PDT