Static fatigue of quartz

Nearly 200 samples of single-crystal quartz were broken in uniaxial compression. The quartz was observed to exhibit strong static fatigue, the mean fracture time 〈t〉 being related to stress σ, concentration of water CH,O, and temperature T by 〈t〉 = t0 CH2O−;α exp [(u′/RT) − κ′σ]. Microfracturing associated with crack growth and spalling occurred continuously during the experiments. No creep strains could be detected. The rate of microfracturing n followed the expression n = a0 CH2O α exp [(−u′/RT) + κ′σ]tγ. These and other results suggest that static fatigue of quartz is due to stress corrosion cracking. The most likely mechanism is a silica hydration reaction. Static fatigue is suggested as the mechanism of brittle creep of rocks and of time-dependent earthquake phenomena.