Altered pyrochlore from the Szklary rare-element pegmatite, Lower Silesia, Poland

Research on pyrochlore (Nb>Ta) from the Szklary rare-element pegmatite (Lower Silesia, Poland) was aimed at its alteration due to action of hydrothermal solutions. The pyrochlore analysed, itself a product of the alteration of manganocolumbite, at later stages was subjected to further alteration by low-temperature hydrothermal solutions or meteoric waters. These processes consisted in incorporation of water into the pyrochlore structure in amounts higher than 1+3/8m, and formation of hydropyrochlore, most probably representing transitional members of a solid solution between the pyrochlore and a hydroksyl analog of hypothetical Ca₂Nb₂O₇ or Ca₃Nb₂O₈ phases.