The fracturing of granite and single crystal quartz at sub- and supercritical hydrothermal conditions was investigated in order to advance the utilization of enhanced geothermal (reservoir) systems (EGS). No changes (i.e., fracturing) were observed at dry conditions, for both granite and single crystal quartz (at any temperature-pressure conditions), but fracturing was recognized in wet conditions. In the experiments, fracturing was accelerated in the presence of water. Optimal conditions for hydrothermally-derived fracturing (HDF) of granite are proposed. HDF is expressed in terms of physico-chemical fracturing under hydrothermal conditions.