Dear Dr. Latha:

Apart from rare metal pegmatites and granites, carbonatites and the related alkaline magmatitic rocks  are the main primary source for Nb and Ta. There are many Nb-bearing minerals which may be categorized as follows and expected in carbonatites:

Columbite group

Ferrocolumbite Fe2+Nb2O6 (78 wt. % Nb2O5 ) rarely

Fergusonite-samarskite group

Fergusonite La0.2Ce0.4Pr0.1Nd0.2REE0.1Nb0.9O4 (41 wt. % Nb2O5 )

SamarskiteY0.2REE0.3Fe3+0.3U0.2Nb0.8Ta0.2O4 (35 wt. % Nb2O5 ) rarely

Pyrochlore-microlite group

Pyrochlore Na1.5Ca0.5Nb2O6(OH)0.75F0.25 (75 wt. % Nb2O5 )

Microlite Na1.5Ca0.5Ta2O6.6(OH)0.3F0.1 (83 wt. % Nb2O5 )

Polyrutile group

Tapiolite (Fe,Mn) (Ta,Nb)2O6 (5.8 wt. % Nb2O5,  73 wt. % Ta2O5) rarely

Perovskite group

Loparite (Na,Ca,Ca) (Ti,Nb)O3 (9.7 wt. % Nb2O5,  0.75 wt. % Ta2O5)

The major members or namesakes of each group are given and their chemical composition and contents in wt. % are  shown in brackets. Rarely means more frequently in pegmatites and granites.

With kind regards

H.G.Dill

p.s. sorry for not considering the subscripts and writing it in this unconventional manner.

Great to have such a detailed answer...Thanks a lot.

Dear Dr. Latha,

There are still some more (important) niobium minerals which can occur in carbonatites:

Natroniobite NaNbO3

Isolueshite (Na,La)NbO3

Lueshite NaNbO3

Pauloabibite NaNbO3

For more information, I recommend the internet portal mindat.org

Best regards,

Guenter Grundmann

Dear colleagues:

The Nb minerals listed by Dr. Grundmann are members of the perowskite group s.s.s. as shown above by the simplified structure (Ca, Na, LREE, Ba, Sr) (Nb, Ta, Ti, Fe)O3

Even the mineral perowskite contains moderate amounts of Nb often associated with LREE (Ce group) for charge balance reasons in carbonatites.

Loparite is among others common to the largest laccolitic alkaline magmatic complex at Lovozero, Russia,

Best regards

H.G.Dill

Dear Dr. Latha:

The following may useful for  Nb bearing mineral

Best regards

Mohammed

Thanks a lot for all your valuable guidance.

And also the pretty rare niocalite, which is a wöhlerite-related sorosilicate in addition to all those oxides mentioned above. Nb may also occur as minor element in Ti-bearing silicates appearing in peralkaline rocks, such as titanite, melanite garnet, etc.