Abstract: The self diffusion of oxygen has been studied in prepared natural crystals of albite, grossular garnet, quartz, and ruffle by isotope exchange with hydrothermal water enriched in ¹⁸O, and subsequent analysis by ion microprobe. Measured oxygen diffusion coefficients (D) in quartz (‖c) may be described by D = 1.08 × 10⁻¹¹ exp(−31.5 kcal/RT) cm²s⁻¹ at 600−750°C and 1 kbar water pressure. For grossular, D = 2.5 × 10⁻¹⁶ cm²s⁻¹ at 1050°C and 8 kbar, and D = 4.8 × 10⁻¹⁷ cm²s⁻¹ at 850 °C and 2 kbar. All ruffle crystals exhibited variable amounts of corrosion, and an approximate diffusion coefficient of D(‖c) = 3.16 × 10⁻¹⁵ cm²s⁻¹ cm²s⁻¹ was obtained at 1050 °C and 1 kbar. Oxygen diffusion coefficients in albite, perpendicular to (001) faces, have been determined as a function of pressure at 600 °C Between 0.5 and 8.0 kbar pressure no systematic variation in the results was observed and most of the data may be described by D = 4.1 (±0.5) × 10⁻¹⁵ cm²s⁻¹. Slow oxygen diffusion rates in quartz and garnet suggest that these minerals should have high ‘closure temperatures’ for oxygen exchange, and may provide reliable oxygen isotope exchange geothermometers.