[meteorite-list] Schreibersite - Inclusions or Plates?

From: Martin Altmann <Altmann_at_meteoritecentral.com>
Date: Tue Feb 8 06:39:48 2005
Message-ID: <001301c50dd3$6e6b1820$2d539a54_at_9y6y40j>

Hi Jeff,

of course schreibersite can form larger inclusions, irregular shaped - then
it's not looking like the big troilite drops you mentioned, but exactely
like the many cohenite inclusions in the IAB and IIICD irons, which appear
often as little wormlets, irregular blobs with short, rounded tails and
sometimes as rims around the troilite eyes.
Cohenite and schreibersite are so similar in appearance, that one hardly can
keep them apart. Fresh cut both are of bright silvery colour and can later
oxidize to all kinds of grey to yellowish.
The schreibersite is much more brittle than the cohenite and pieces easilier
break off while cutting or grinding (so better grind it by hand).
As it's so difficult to distinguish from cohenite and both together aren't
found very often in a slice, one could say by rule of thumb:
If you have irons not from the IAB or IIICD-complex, the silvery stuff is
schreibersite.
(You'll never find a cohenite inclusion in Sikhote-Alin for instance).
Second, in the IAB/IIICD (like in Morasko, Odessa, Canyon Diablo) there is
much more cohenite than schreibersite.
And in brackets: I observed on the triple rimmed troilite drops always this
order from inside to outside. Inner rim graphite, middle rim schreibersite,
outer rim cohenite.
If you have both, cohenite and schreibersite, that one which is more damaged
by cutting (or that what could be scratched much more easy with a needle) is
schreibersite.

I have to look, whether I have some old pictures left on my computer, for
demonstration. Will mail it to you...

Bye!
Martin



> G'day List,
>
> My very basic knowledge of iron meteorite minerals tells me that
> schreibersite exists as plates between other minerals in the matrix. (E.g.
> Taenite & Kamacite). Have any meteorites been found where this mineral
> exists as relatively large irregular inclusions? (Think like the shape of
> iron sulphides in Dronino or Mundrabilla.)
>
> Thanks,
>
> Jeff Kuyken
> I.M.C.A. #3085
> www.meteorites.com.au
>
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Received on Tue 08 Feb 2005 06:43:38 AM PST