Columbit-tantalit z pegmatitu pri Ráztočne v pohorí žiar (stredné Slovensko).

Accessory columbite-tantalite forms black tabular crystals (0.2 to 2 mm in size) in fine-grained albite-quartz-muscovite parts of granitic pegmatite dike, associated with Hercynian S-type granite, near Ráztočno village in the Žiar Mountains (Tatric Superunit, Central Western Carpathians, Central Slovakia), Columbite-tantalite shows regular oscillatory zoning, generally with increasing Ta/Nb from central to rim parts of crystals. Electron-microprobe analyses reveal dominancy of columbite-(Fe) to tantalite-(Fe) with molar ratios Mn/(Mn+Fe) = 0.17 to 0.25 end Ta/(Ta+Nb) = 0.07 to 0.50. Rarely were also detected columbite-(Mn) compositions with Mn/(Mn+Fe) = 0.66 to 0.79 and Ta/(Ta+Nb) = 0.08 to 0.17. Contents of Ti are low (up to 0.03 apfu, 0.2 - 0.5 wt. % TiO2), concentrations Of W, Sn, Zr, Sc, Mg and Zn are negligible. Secondary microlite replaces the columbite-tantalite along fissures and rims. Studied columbite-tantalite represents a typical example o late-magmatic mineral of less fractionated LCT-suite and beryl-columbite subtype of rare-element granitic pegmatites. [ABSTRACT FROM AUTHOR]