The 110 degrees C thermoluminescence (TL) peak of unfired, synthetic quartz (Sawyer Research Products) has been found to be strongly superlinear with the dose of excitation. Quadratic and nearly cubic dependences have been observed with both beta - and gamma -irradiation. Firing the samples at 300° C or higher increased the sensitivity substantially and removed the superlinearity. The fired samples have been found to have a pre-dose (sensitisation) effect similar to natural quartz, however, the pre-dose effect is weaker than in many of the other types of quartz. A model of competition during the heating phase, previously suggested to explain a quadratic dose dependence, is now shown to be capable of explaining the very strong superlinearity observed with the unfired sample. Furthermore, the model can also be used to account for the observed shifts in the temperature of the TL peak, the linearity and sublinearity of the fired samples, and their higher sensitivity.