[meteorite-list] RFS Picture of the Day => Brenham slice withunusual inclusion

From: tett <tett_at_meteoritecentral.com>
Date: Sun, 21 Jan 2007 22:27:05 -0500
Message-ID: <004201c73dd5$30e682d0$647da8c0_at_Tettenborn>

Bernd,,

Thank you for the research and the comprehensive answer. It is a pleasure
learning from you!

The swathing kamacite sounds like it might be the case here. You are
careful to preface your remarks with caveats but it sure sounds like the
odds are in favour of kamacite. At least per Buchwald and your other
references.

Many thanks,

Mike


----- Original Message -----
From: <bernd.pauli at paulinet.de>
To: <Meteorite-list at meteoritecentral.com>
Sent: Sunday, January 21, 2007 2:27 PM
Subject: [meteorite-list] RFS Picture of the Day => Brenham slice
withunusual inclusion


> Tett asked:
>
> "How can you tell the difference between kamacite
> and taenite? Does the crystal structure give it
> away"?
>
>
> Hello Mike and List,
>
> As I am hardly ever *absolutely* sure I wrote: "If I am not mistaken here"
> ;-)
>
> I'm sure that the crystal structure and the telltale color of the
> inclusion
> would give it away if you could have a close look at it "in person" but
> as I am too far away, my approach is one of "by inference". When there
> are inclusions in iron meteorites (troilite, schreibersite, cohenite,
> etc.)
> and when these inclusions have a rim or a seam of material surrounding
> or enclosing them, then it is usually "swathing kamacite". Those among us
> who are fortunate enough to own the Buchwald trilogy, will be able to
> produce numerous pictures from Buchwald where one can clearly see this
> phenomenon and then deduce by comparing several pictures and, of course,
> Buchwald's description of these phenomena that it is what it is. One such
> example is figure 153 on page 105 of Buchwald (Vol. 1). You can see a
> picture of the Grant medium octahedrite and it shows several of these
> "oriented schreibersite lamellae, each of which displays rims of swathing
> kamacite". Another picture of the same iron is to be seen on page 107, a
> textbook example of a "troilite nodule with ... well-developed swathing
> kamacite".
>
> Buchwald is such a precious treasure trove of information! When a list
> member
> asked me about these "needle-like" inclusions a few days ago, I was able
> to
> confirm (of course with the help of Buchwald!) that these inclusions are
> in
> all probability so-called Brezina-lamellae and this again, by inference
> from
> information culled from Buchwald who writes that if phosphorus is
> abundant,
> the angular plate-like crystals [of schreibersite] may be seen to be
> oriented.
>
> And thus, once again by inference, (although I do not know how high the P
> content in Brenham is), one may conclude that Brenham has an appreciable
> amount (above ca. 0.4% P - according to Buchwald) of phosphorus. Other-
> wise we wouldn't see those beautiful, long, needles of schreibersite with
> their seams of swathing kamacite.
>
> Cheers,
>
> Bernd
>
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Received on Sun 21 Jan 2007 10:27:05 PM PST