Shock wave data to provide an equation of state of muscovite (initial density: 2.835 g/cm3) were determined up to a pressure of 141 GPa. The shock velocity (Us) versus particle velocity (Up) data are fit with a single linear relationship: Us=4.62(¿0.12)+1.27(¿0.04)Up (km/s). Third-order Birch-Murnaghan equation of state parameters (isentropic bulk modulus and isentropic pressure derivative of bulk modulus) are KOS=52¿GPa and K'OS=3.2¿0.3. The pressure-temperature relation along the Hugoniot suggests that muscovite may dehydrate to KAlSi3O8 (hollandite), corundum, and water, with a small volume change, above 80 GPa. Thermodynamic calculations of the equilibrium pressure for the dehydration yields a significantly lower value. Observed unloading paths from shock pressures up to about 80 GPa are steeper in a density-pressure plane than the Hugoniot and become shallower with increasing shock pressure above that pressure. The changing slope may indicate that devolatilization occurs during unloading above 80 GPa. The present equation of state data for muscovite are compared with results of previously reported recovery experiments. ¿ American Geophysical Union 1991