[meteorite-list] comments from Bernd (blue hibonite)

From: Zelimir Gabelica <Z.Gabelica_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:29 2004
Message-ID: <1.5.4.32.20040227073441.008cceb4_at_pop.univ-mulhouse.fr>

Hello Michael, Eric, Terry... (Bernd ?)

Just a comment about the Ti3+-containing blue hibonite.=20

Ti3+ is paramagnetic and currently gives a characteristic EPR (Electron
Paramagnetic Resonance) signal, especially if it is "diluted" as solid
solution in another crystalline phase such as hibonite (I suppose Ti3+
partly replaces Al3+ in the hibonite structure).=20
Ti3+ is indeed very rarely stabilized on Earth where it should readily
oxidize to Ti4+, found in most of the minerals (Ti4+ is diamagnetic and thus
not "active" in EPR).
Conversely, Ti3+ is very likely to occur in space or on asteroids that do
not have an oxidative atmosphere (vacuum is a reducing medium).

This being, running an EPR spectrum could perhaps help definitely
identifying the presence of blue hibonite in Terry's CV3's, provided Ti3+
did not totally oxidize to Ti4+ during the terrestrial life of the meteorite
(possibly it should not if we deal with a real solid solution).=20
To run such a spectrum, a few mg of folid is quite enough, as ppm Ti3+
concentrations are enough for a signal to be recorded (the more diluted the
system, the sharpest the signal).

During my past research I used to run such spectra regularly and could get
quite familiar in interpreting Ti3+ EPR signals. Presently, I don't have any
EPR equipment in my new lab but if some investigation is needed, I can
contact some friend scientist involved in EPR, ask him to run some spectra
on your powder and this perhaps would help telling more about these blue
inclusions in the CV3.

Just a suggestion. Tell me if there is interest.

Best wishes,

Zelimir
--------

At 17:33 26/02/04 -0800, you wrote:
>Hi all,
> Bernd sent me this commentary today and I asked his permission
>to post it to the list:
>
>Today E. Olson posted some-
>thing about blueish hibonite crystals in Terry Boswell's CV3's and
>so I sent a private mail to Eric informing him that blueish hibonite
>(CaAl12O19) components are commonly found in CM2's but that
>they are rare in the Allende CV3 chondrite. I also added that, in CM
>chondrites like Murchison, Ti-bearing hibonite is blue, while it is tan
>or orange in Allende. The color difference is due to the presence of
>trivalent titanium (Ti3+) in blue hibonite whereas orange hibonite does
>not contain Ti3+. So if Terry's CV3s really contain b l u e hibonites,
>this would be a rare occurrence - Vigarano being the only exception.
>
>PS: Bernd is considering returning to the list. He left in protest of
>continual negative postings. If we want him back - especially for
>good, we will have to abandon past practices of attacking one
>another on the list.
> Best wishes, Michael
>
******************************************************
Prof. Zelimir Gabelica
Groupe S=E9curit=E9 et Ecologie Chimiques (GSEC) - ENSCMu
3, rue A. Werner
F-68093 MULHOUSE Cedex, FRANCE
Tel: +33 (0)3 89 33 68 94
FAX: +33 (0)3 89 33 68 15
e-Mail: Z.Gabelica_at_uha.fr
******************************************************
Received on Fri 27 Feb 2004 02:34:41 AM PST