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Identity HelpCheralite?

3rd Nov 2008 06:45 UTCIlkka Mikkola Expert

Hello


From the Viitaniemi-pegmatite,Eräjärvi,Orivesi,Finland.Microprobe:SiO2 13.5 CaO 14.7 ThO2 54.3 P2O5 16.2 Tot 98.7(w%).

Could it be cheralite,it is a small grain with F-apatite and thorianite.


Ilkka

3rd Nov 2008 07:17 UTCStuart Mills Manager

Based on that: huttonite 62%, cheralite 38%. You're missing some REE or U. But you have huttonite. Is there more info?


Stuart

3rd Nov 2008 08:23 UTCIlkka Mikkola Expert

Hello Stuart


Si missing: SiO2 13.5(w%).Too much Ca for huttonite? I think that total is quite good.I have no more info,the grain is so small.


Ilkka

3rd Nov 2008 17:51 UTCStuart Mills Manager

I just recalculated and got 51% huttonite and 49% cheralite, so this appears to be somewhere around the 50:50 join in the solid solution series. Is it only one grain that shows this? It's composition is interesting.

3rd Nov 2008 19:47 UTCIlkka Mikkola Expert

Hello


It is only a small about 0,4 mm grain in a SEM-photo of brown F-apatite with little thorianite. However about

1/3 of the small sample is either huttonite/cheralite or thorianite in the SEM but no other points analyzed.

Apatite is almost black and huttonite and thorianite ligth grey and white in the SEM.

I thougth that it could be monazite and sent it to microprobe.


Ilkka

3rd Nov 2008 20:54 UTCPavel Kartashov Manager

I never met thorianite in quartz bearing assemblages, but only in silica unsaturated ones - magnesial skarns, carbonatites. etc. ThO2+SiO2 = ThSiO4... ;) May be this your thorianite is uraninite or at least bröggerite?

4th Nov 2008 17:05 UTCIlkka Mikkola Expert

Hello Pavel


Thorianite (Th 0,68 U 0,32)1,00 O2 with apatite in montebrasite(with rutile,anatase ,viitaniemiite,eosphorite and

over ten cm morinite with crandallite.


Ilkka

4th Nov 2008 19:58 UTCPavel Kartashov Manager

Hello Iikka,

apparently this is huge phosphate segregation and thorianite in it is later formed during decomposition of some primary pegmatite mineral. So this new formed thorianite hadn't contact with quartz. This is rare situation. Most of thorianites in the world were formed in quartz-free rocks.

By the way, it is interesting to see morinite from Viitaniemi - its photos absent on mindat. Do you have some material for exchange?

Kind regards,

Pavel

5th Nov 2008 15:55 UTCIlkka Mikkola Expert

Hello Pavel

I have sent you a personal message.

Ilkka
 
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