(A) Composition of studied CGM grains in the quadrilateral Ta/(Ta + Nb) versus Mn/(Mn + Fe) diagram. Enrichment tends of Ta and Nb (grey arrows) observed for CGM from various types of pegmatites according to Černý (1989). (B) Sn + Ti + Zr vs. Mn/(Mn + Fe) (atoms per formula unit, apfu) binary diagram showing a poorly defined general trend of M⁴⁺ traces impoverishment with increase of (Mn/Mn + Fe) ratio. (C and D) Trace element vs. Ta + Nb + Mn + Fe (apfu). (E) Zr + Ti vs. Sn (apfu) binary diagram showing the correlation between Zr, Ti and Sn in columbite-tantalite grains within almost all pegmatites fields. (F) U vs. Sn (apfu) binary diagram showing the lack of correlation between the uranium and the tin contents within studied columbite-tantalite grains.