Hi everybody!
Funny to realize that geologist never stop working during "holiday time" :)
What about rutile (TiO2)?
Rutile exsolution might have issued from a prograde biotite (Ti-rich) reacting to muscovite + rutile (+ garnet or cpx +...). If these are some biotite lamellae inside white mica, then a clear 0° extinction angle should be observed.
Otherwise, I agree with D. Papineau, looking at EDS even on some "mixed excited volume" (i.e. unknown mineral + mica) can be useful. It should at least show a distinct and pretty high Ti-Ka peak compared to a EDS spectrum on the host mineral (muscovite). If that is Fe-bearing minerals (or ilmenite), then both Fe (and Ti) peaks should be distinguishing feature.
Do you have other Fe- or Ti-bearing accessory minerals in the matrix or as inclusion in garnet or clinopyroxene?
All the best for 2010,
Julien Allaz
On Dec 30, 2009, at 5:55 PM, Pavel Pitra wrote:
> Hello,
>
> studying glaucophane + cpx + grt-bearing rocks from Syros (Greece) and Ile de Groix (France), I recently came across a tiny but outstanding mineral that I am ashamed to admit not to be able to identify. It occurs in several samples from both localities, but I never saw it so clearly in other rock types (at least I don't remember). I'm attaching three photographs of it and would be very grateful for a suggestion.
>
> It is brownish-red to orange, slightly pleochroic with relatively high relief and occurs typically as very thin lamellae (inclusions?) in white micas, apparently parallel to the cleavage. Locally it also ocurs in garnet. It is so thin that the optical properties interfere strongly with the mineral hosts. I'm afraid that for the same reason microprobe analyses wouldn't be conclusive either. Normally I would neglect it as a "iron hydroxyde", but its attractive appearance in these sections (and the fact that it seems enjoy such mineral assemblages) prevents me from doing so.
>
> Thanks a lot for any suggestions!
>
> Have a nice end of the year, and a good new one!
>
> Cheers,
>
> Pavel
>
> --
> Pavel PITRA
> Geosciences Rennes email: [log in to unmask]
> Université Rennes 1 tel: (++33) 2.23.23.65.06
> Campus de Beaulieu - Bat. 15 fax: (++33) 2.23.23.60.97
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> http://www.geosciences.univ-rennes1.fr/rubrique.php3?id_rubrique=71<redwm2-5x.jpg><redwm2-10x.jpg><redwm1.jpg>
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Dr. Julien Allaz
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A short introduction about my PhD thesis... (University of Berne)
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