Laumontite is a common and potentially frictionally-unstable hydrothermal alteration product present in deep faults of the Gonghe EGS reservoir. We characterize the friction-stability characteristics of synthetic laumontite gouge under in situ reservoir conditions. The gouge is frictionally strong (μ=0.73–0.98) with quartz/laumontite mixtures (1:1) generally less strong (μ=0.73–0.78) with both largely independent of temperature but increasing with elevated pore pressure. The pure gouge and mixture are strongly velocity-weakening over a broad range in temperatures (~90–220℃) and excess pore pressures (0–90MPa) relevant to the Gonghe stimulation. Microearthquakes (MEQs) observed during stimulation are confined to within the broad depth range of inferred frictional instability – although fluid overpressures are also limited to this region. The observation that laumontite mixtures are frictionally unstable over a broad range of pressures and especially temperatures representative of EGS reservoirs and insensitive to the proportion of the coexisting mineral phase suggests its presence is a strong indicator of potential seismic hazard – and thus worthy of careful consideration.