All,
One has to be very careful in analyzing Cr in any ferroan phase if
there is a high-Cr mineral such as chromite within 50 microns. This is
a result of the highly efficient fluorescence of Cr by even low Fe in
the unknown.
eric
On Nov 15, 2004, at 9:32 AM, christian chopin wrote:
> Dear Erling,
>
> if my memory serves me well, Mg-Cr-rich staurolite weas described from
> Cabo Ortegal by Gil-Ibarguchi et al. (Am. Min. paper?) and from
> New-Zealand, Fiordland, by Ward (ca. 1984). Interestingly, at lower T
> (but still high P), Mg-Cr-rich chloritoid may play the same role in
> metabasites (e.g. Messiga et al. from the Voltri Zone).
> You may also have a look at a paper by Michel Demange (Bull.
> Mineralogie, ca. 1980) on staurolite-bearing amphibolite from Ovala,
> Gaboon. They may well contain Cr.
>
> Best regards
> Christian
>
> A 14:39 15/11/04 +0100, vous avez écrit :
>
>> Dear all,
>>
>> We are currently working on prograde HP/UHP metamorphism of
>> ultramafic rocks from the eclogite-bearing uppermost Allochthon of
>> the Caledonides. One of the rock types we have found mainly consists
>> of the rather rare assemblage pyrope-rich garnet + pargasite +
>> zoisite. In garnet and pargasite we have found tiny inclusions of
>> Mg-rich staurolite. In one sample staurolite included in Cr-pargasite
>> contains considerable amounts of Cr, which also seems to be unusual.
>>
>>
>>
>> Average compositions of staurolite from these two samples are
>> (normalized to 100%):
>>
>>
>>
>> In grt In Cr-pargasite
>>
>> SiO2 27.31 28.11
>>
>> Al2O3 59.90 53.94
>>
>> Cr2O3 5.68
>>
>> FeO 4.38 3.64
>>
>> MgO 8.40 8.63
>>
>>
>>
>> Does anyone know about Cr-bearing staurolite from other areas?
>>
>>
>>
>>
>>
>> Erling
>
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>
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