The concentration of copper and zinc in silicate rocks was determined by atomic absorption spectrophotometry, a new method of chemical analysis. Limits of detection in solution of 0.026 ppm Zn and 0.12 ppm Cu allowed samples to be run directly in solution with a 1:50 dilution. Matrix interferences are not significant. Precision for copper ranged from 34% at 5 ppm to 3.3% at 218 ppm in the sample. Precision for zinc ranged from 9.7% at 3 ppm to 3.7% at 260 ppm in the sample. Atomic absorption compares well to neutron activation analysis in precision and accuracy, and atomic absorption is more rapid. The precision and accuracy of atomic absorption analysis for copper and zinc in silicate rocks is very good for a method so simple and quick. The "best value" of 13 ppm copper in G-1 appears to be warranted. W-1 appears to have a "best value" of 115 ppm copper and 85-91 ppm zinc. G-1 probably contains between 44 and 49 ppm zinc. Atomic absorption should find wide use in geochemistry as a method for the trace element analysis of rocks, minerals, soils, plants and water samples.