Minute crystals of columbite occur in tungstate ore in the quartz veins at Carrock Fell Mine. Accompanying wolframite crystals show pronounced niobium enrichment adjacent to growth faces. The columbite grains, however, occur as inclusions in minerals formed during metasomatic replacement of the wolframite. They are chemically variable, containing 7–18 % WO₃ by weight, up to 1.9% Sc₂O₃, and up to 4.7% TiO₂. Tin, a common minor element in columbite, was not detected. The columbite grains are spatially associated with carbonate minerals involved in wolframite replacement, and it is suggested that their formation occurred principally when carbonate precipitation caused a reduction in the stability of dissolved niobium complexes.