[meteorite-list] Schreibersite & Cohenite

From: Martin Altmann <Altmann_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:56 2005
Message-ID: <005201c52727$48294840$284e9a54_at_9y6y40j>

Hi Jeff and Bernd,

I think, this may be meant for fresh cut samples, as schreibersite and
cohenite both can show all shades or nuances of yellow or gray, if they
start to oxydize.
That's why Norton also suggests a semidestructive test in his book.
In my practical view schreibersite is more brittle than cohenite, breaks off
more easy while cutting and will be more easilier damaged, if you grind your
specimen by machine and not by hand.
And my thumb-rule for handpieces is: cohenite doesn't appear in remarkable
amounts in other irons than those of the IAB-IIICD complex
(which can of course have additional schreibersite too).
Furthermore, these wormshaped inclusions, which are oriented parallely to
the Widmannoops to the fields of the Thomson structures, turned out until
now always to be cohenite.
Another observation I made is, that if you find a troilite eye with several
rims of graphite, schreibersite, cohenite, there the cohenite will be always
the more outer rim, than the schreibersite.
And last but not least, it's impossible to judge from photos, just another
angle of light and that, was seemed to be brilliant cohenite and that what
was more dull schreibersite, will be turned otherwise round. You may watch
out on ebay for a cheap Odessa or Morasko, sometimes also Canyon, which has
both minerals (sometimes in direct contact), so that you have a specimen for
comparing, if you aren't sure.

Buckleboo!
Martin


----- Original Message -----
From: <bernd.pauli_at_paulinet.de>
To: <info_at_meteorites.com.au>; <meteorite-list@meteoritecentral.com>
Sent: Saturday, March 12, 2005 2:55 PM
Subject: Re: [meteorite-list] Schreibersite & Cohenite


> > Is there a relatively easy and reliable way to visually
> > pick the difference between Schreibersite and Cohenite
> > in iron meteorites?
>
> Hello Jeff and List,
>
> Here is some information from Buchwald that may prove helpful
> in identifying schreibersite and cohenite in hand samples:
>
> Buchwald V.F. (1975) Handbook of Iron Meteorites, Vol. 1:
>
> Cohenite (p. 100):
>
> - cohenite is brilliant w h i t e
> - it is very hard, significantly harder than schreibersite
> - characteristic of group I irons (also occurs in other irons)
>
> Schreibersite (p. 104):
>
> - schreibersite is magnetic
> - it is y e l l o w in reflected light
> - compared to cohenite distinctly more brownish
> - softer and much more brittle than cohenite
>
> See also: O.R. Norton (2002) Cambridge Encyclopedia of
> Meteorites, Appendix C, Minerals in meteorites (pp. 311-313).
>
> Best wishes,
>
> Bernd
>
> To: info_at_meteorites.com.au
> meteorite-list_at_meteoritecentral.com
>
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Received on Sat 12 Mar 2005 12:16:50 PM PST