We have measured the effects of pressure, temperature, and some variations in impurity content on the growth rateuof quartz into fused silica. Under all conditions the growth rate was interface controlled and increased exponentially with pressure with an activation volume averaging −21.2 cm3/mole. The activation enthalpy for all specimens extrapolated to a zero pressure value of 64 kcal/mole, within the experimental uncertainty. At a given stoichiometry the effect of hydroxyl content on growth rate is described entirely by a linear termCOHin the prefactor of the equation for the growth rate. The effect of chlorine impurity can be described similarly. Alsouis increased as the ideal stoichiometry is approached from the partially reduced state.