Niobian rutile with substantial W content is associated with black tourmaline, beryl, zircon, xenotime-(Y), monazite-(Ce), "písekite", and possibly pseudorutile or pseudobrookite in two cogenetic, beryl-columbite-subtype, granitic pegmatites at Písek and Údraž, southern Bohemia, Czech Republic. Crystals, up to 3×1 cm in size, consist of relics of a primary, phase-homogeneous but oscillatorilly zoned niobian rutile phase and of exsolution intergrowths of depleted niobian rutile with granular titanian-tungstenian ixiolite. Primary niobian rutile has the monorutile structure and shows extensive substitution (Fe, Mn, Mg) 2+ +1 (Nb, Ta) 5+ +2 Ti 4+-3 (up to 26.34 wt. % Nb 2 O 5 and 8.60 wt. % Ta 2 O 5 ; 26 to 37 mol. % columbite component), significant (Fe, Mn, Mg) 2+ +1 W 6+ +1 Ti 4+-2 (up to 3.12 wt. % WO 3) and minor (Fe, Sc) 3+ +1 (Nb, Ta) 5+ +1 Ti 4+-2 substitutions. The values of Fe 2+ /(Fe 2+ + Fe 3+) are high and average at ~ 0.8. Oscillatory zoning is controlled by Nb, Ta and Fe; variations in W are independent and erratic. Depleted niobian rutile still contains 8 to (rarely) 32 mol. % ferrocolumbite component. Individual grains of the exsolved orthorhombic ixiolite are commonly heterogeneous in terms of the W content. They display highly variable degree of the substitution Fe 2+ +1 W 6+ + 3 Nb 5+-4 (up to 49.00 wt. % WO 3), moderate but widespread (Ti, Zr, Hf) 4+ + 3 (Fe, Mn, Mg, Ca) 2+-1 (Nb, Ta) 5+-2 (up to 9.83 wt. % TiO 2 , 1.94 wt. % ZrO 2), and subordinate (Fe, Sc) 3+ + 3 (Fe, Mn, Mg, Ca) 2+-2 (Nb, Ta) 5+-1 (up to 1.51 wt. % Sc 2 O 3). Exsolution reveals the preference of Sn 4+ and Fe 3+ for the rutile structure, whereas Fe 2+ , Mn, Mg, Nb, Ta, Sc, Zr, Hf and W are concentrated in the ixiolite. The results confirm the extent of the W substitution in pegmatitic niobian rutile and its significance for the style of subsolidus breakdown, on par with the magnitude of effects exerted by (Nb > Ta + Fe 2+), (Nb > Ta + Sc + Fe 3+), (Nb > Ta + Fe 2+ /Fe 3+~1), or (Fe/Nb > 0.5).
