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When an x‐cut quartz disk is subjected to an impulsive load, the piezoelectric current in an external short circuit is ordinarily an accurate time‐resolved replica of the stress history at the input electrode. Recently, it has been observed that stress pulses whose durations are less than the shock‐wave transit time through the disk sometimes produce anomalous current‐vs‐time responses. In the present work, x‐cut quartz disks are subjected to stress pulses of six different durations and with amplitudes from 9 to 29 kbar. Carefully controlled accurately known pulses are applied to the samples by the impact of projectile‐mounted quartz disks of various thicknesses. The piezoelectric current accompanying each stress pulse is continuously monitored as the pulse propagates through the sample disk. It is found that the anomalous current is a consequence of shock‐induced conductivity in the region of the quartz disk that has been shock loaded and subsequently unloaded to a lower stress value. The threshold for conductivity is found to depend upon both stress amplitude and pulse duration. The threshold is further determined to be controlled both by a critical unloading stress value and by a critical electric field value. The critical unloading stress value is found to be 11.2±0.7 kbar, and the critical electric field is found to be (2.8±0.3) ×105V/cm.