The niobium concentrations in 15 U.S.G.S. standard rocks were measured by neutron activation analysis. The niobium was separated from the rock matrix (in the presence of95Nb tracer, which was used to measure the fraction recovered) before irradiation to improve the sensitivity. Results of this work are compared with those obtained by other techniques. Some results obtained by multielement X‐ray fluorescence procedures agree well with the present data, but a systematic disagreement exists between these and the spectrophotometric dat