AW: [meteorite-list] Dronino

From: Jörn Koblitz <koblitz_at_meteoritecentral.com>
Date: Mon Aug 9 06:45:28 2004
Message-ID: <E5E6112EA31FA24CB448E091C6883C050EBC8F_at_server2000.microfab.de>

Hi list,

When I looked at the Dronino pictures with the etched surface, I instantly thought of Tishomingo, which is a high-Ni iron with martensite, a low-temperature shock-induced lattice transformation phase out of taenite, well known for terrestrial steel - but in Tishomingo much better developed. The problem is that Dronino got much lower Ni content than Tishomingo, which makes it difficult to explain martensitic transformation, if the meteoroid did not experienced some violent and rather exotic thermal and shock history. On the other hand, a martensite could explain the finiding by Marcin, that his pieces doesn't show any pattern. Martensite transformation of supercooled taenite can be triggered by shock waves running through the body. So, it may only be locally present (somehow like the shock darkening of some ordinary chondrites)!

The description given in the Meteoritical Bulletin ("the Dronino iron is an ataxite containing sulfide inclusions (~10 vol.%) and consisting of kamacite (7.0?0.5 wt% Ni and 0.75 wt% Co) and rare taenite (26.5?0.5 wt% Ni and 0.35 wt% Co) as elongated precipitates (1-3 ?m in size) which form linear and banded textures...") also rises a question: how can taentite PECIPITATES from kamacite? Usually, it is the other side round: kamacite precipitates from taenite (the high-temperature phase of iron) when the meteorite parent body slowely cooled down. The precipitated kamacite grow from tiny lamellae to larger bands and the taenite lamellae found in such irons are just remains of the originally monocrystalline taenite body.

Best regards,
J?rn

_______________________________________________________________________________
Joern Koblitz
MetBase Editor
The MetBase Library of Meteoritics and Planetary Sciences
Benquestrasse 27
D-28209 Bremen, Germany
phone: +49 421 24 100 24
fax: +49 421 168 2799
email: info_at_metbase.de
_______________________________________________________________________________




> -----Urspr?ngliche Nachricht-----
> Von: Martin Altmann [mailto:Altmann_at_Meteorite-Martin.de]
> Gesendet: Montag, 9. August 2004 02:30
> An: bernd.pauli_at_paulinet.de; Meteorite-list@meteoritecentral.com
> Betreff: Re: [meteorite-list] Dronino is an (ungrouped) ataxite
>
>
> Hi list and Bernd,
>
> the camacite needles or spindles in Taza are very sharp
> defined and come out
> very contrastful after etching. If there are a lot of
> spindles, they are
> often so oriented, that they indeed are imitating a kind of a
> "Widmannst?ttern pattern", but not very similar to Dronino.
>
> IVA - that's a good point!!
> Take a look again on that slice on ebay. One can clearly see,
> that it's
> composed of three large crystals, wherein the orientation of
> the "pattern"
> shows different orientation - almost the complete left half,
> then upper part
> to the right and bottom right -
> seperated well visible by the dark clefts.
>
> Immediately when I saw this slice, Gibeon came in my mind,
> where also such
> composed slices can be found.
> (Take f.e. a look in your Buehler, page 120).
>
> Dronino is a real uncommon iron!!
>
> Martin,
>
> (also from Southern Germany with a perfect sky for catching
> perseids. Hope
> it will last until the maximum)
>
> ----- Original Message -----
> From: <bernd.pauli_at_paulinet.de>
> To: <Meteorite-list_at_meteoritecentral.com>
> Sent: Sunday, August 08, 2004 11:45 PM
> Subject: [meteorite-list] Dronino is an (ungrouped) ataxite
>
>
> > Marcin wrote:
> >
> > > Pattern is strange. Only idea I just have then was, that
> this looks
> strange
> > > like Taza. Of course this is not the same, but this looks the same
> strange
> > > like Taza pattern, I not know any other similar pattern like from
> Dronino.
> >
> > Hi List,
> >
> > The Meteoritical Bulletin, No. 88 can shed some light on
> this Taza-like
> structure.
> > What you are looking at is probably taenite present as elongated
> precipitates
> > with sulfide inclusions rounded and elongated along the banding.
> >
> > But one thing is for sure: it is a very exotic iron
> meteorite because, on
> the one
> > hand, it is closely related to IVA irons, whereas, on the
> other, its low
> Au and Ga
> > contents clearly distinguish the Dronino element pattern
> from that of any
> known
> > iron meteorite group.
> >
> > ______________________________________________
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>
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>
Received on Mon 09 Aug 2004 06:48:25 AM PDT


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