Sarah,
Sorry if you have hear back on this already. You certainly can [and probably 'should'] analyze F in biotite, especially in granulites [probably Cl as well]. On the microprobe we usually use a TAP crystal, but you might get higher count rates on a light-el. crystal such as LDE1. The beam should be defocused, and a good idea also is to check for 'burn' effects [count-rate drop over time for F].
I would expect you probably can find abundant references to F and biotite stability; one that comes to mind immediately is the MSA reviews Mica volume[13], ch. 11 [munoz]. A georef or similar search likely will turn up some recent articles. I also recall some articles several years back on ammonium substitution, at least one from Brittany(?) rather near you there [in AJS?].
Good luck.
>At 05:01 10/12/99 +0200, Sara Welley wrote:
>
>Hello Everyone,
>
> I noticed in some papers on granulites that the
>tables of chemical composition of biotite do not
>contain
>fluorine (F), is it because its
>not possible to analyse fluorine in biotite (?), if we
>can analyse it, could someone tell me how? I would
>appreciate if you could help me also with the relevant
>references on the effect of
>fluorine on biotite stability at high metamorphic
>grade?
>Many thanks in advance for your help.
>Sara
>
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