Automted equipment is used to generate selenium hydride from solutions of rock samples prepared by digestion with a mixture of hydrofluoric, perchloric, and nitric acids. The evolved hydride is swept by argon into an electrically heated quartz tube atomizer. The atomic absorption of Se is measured at 196.0 nm. 1, 10-phenanthroline is used to minimize interferences from copper and nickel. The practical detection limit of selenium in rock samples is 0.05 pp. Results for reference rock samples agree closely with published values.