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Identity HelpRe:Allanite

26th Jun 2007 18:44 UTCIlkka Mikkola Expert

Allanite(Wt%) SiO2 32.2 Al2O3 17.4 Fe2O3 16.3 MnO 5.2 CaO 5.1 Ce2O3 8.4 La2O3 3.0 Nd2O3 4.2 Sm2O3 1.3 Y2O3 3.7 Tot 96.8.

Allanite(Ce).Why? Ca and Mn more than Ce


Ilkka Mikkola

26th Jun 2007 19:15 UTCJohan Kjellman Expert

I wont argue - but one aspect might be that the atomic ratio of the rare earths vs. the Ca. In fact there should be some more elements there to really rely on this analysis.


cheers

26th Jun 2007 19:35 UTCUwe Kolitsch Manager

It's simply a question of site occupancy (in epidote-group minerals we have two sites, A1 and A2, which can host Ca, Sr, Pb, Mn and REE - the REE being basically restricted to the A2 site) and the 50% rule.


See the following refs.:

Armbruster, T., Bonazzi, P., Akasaka, M., Bermanec, V., Chopin, C., Gieré, R., Heuss-Assbichler, S., Liebscher, A., Menchetti, S.; Pan, Y. & Pasero, M. (2006): Recommended nomenclature of epidote-group minerals. European Journal of Mineralogy 18, 551-567.

Ercit, T. S. (2002): The mess that is "allanite". Can. Mineral. 40, 1411-1419.

26th Jun 2007 23:29 UTCJohan Kjellman Expert

Uwe you are of course right - but I think were Ilkka got confused is with how Mindat writes the formula (CaCe)...evidently with Ca>Ce how can it then be a REE-dominant mineral?

Maybe Mindat should shape up on the formulas - making them more structural...

26th Jun 2007 23:34 UTCPavel Kartashov Manager

Dear Ikka,


your analisis is squint, but it is possible to recalculate it on allanite formula in the first approximation as: (Ca.52Mn.42)0.94(Ce.29Y.19Nd.14La.11Sm.04)0.77(Fe".50Fe"'.68Al1.97)3.15Si3.09O12(OH)


So we have here a member of allanite-uedaite serie from allanite side. And from point of view of systematic and 50% rule it is "usual" allanite-(Ce).


Of course it is quite unusual according to its REE distribution and high Mn content. Some tens years ago such varieties had named "manganorthite". Many such analyses were published by Japanese investigators from pegmatites, a number one was published from Southern Ural too.


It is interesting to me where you found this mineral and who made this analysis?


Kind regards,

Pavel

26th Jun 2007 23:39 UTCPavel Kartashov Manager

Ilkka, sorry, I'd lost one letter from your name. :(


Johan is quite right. Allanite formula should be given as (Ca,Mn)(REE,Ca,Sr,Pb)Fe"AlAlO(OH). It is ortho-diorthosilicate.

27th Jun 2007 08:22 UTCIlkka Mikkola Expert

Thank you all

My allanite formula is wrong(Ca,Mn,Ree)..

This sample is from the Pyörönmaa pegmatite,Finland.Analysis:Anton Pilipiuk St

Petersburg,Russia.

Ilkka

27th Jun 2007 08:58 UTCUwe Kolitsch Manager

Have added allanite-(Ce) to the locality file.
 
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