The available shock-wave data for solid .a quartz in the stishovite pressure regime are reduced to a 25øC isotherm and an adiabat, centered at standard conditions, using recent standard density, enthalpy, and coefficient of thermal expansion data. The calculated isothermal bulk modulus, 3 Mb, as determined from the Bireh-Murnaghan equation, depends critically on the value of (dK/dP)•, at zero p...