Acoustic emissions from stress-induced dauphiné twinning in quartz

Dauphiné (electrical) twins have been introduced into quartz crystals by means of suitably oriented mechanical stresses. Stress-induced twinning was observed optically by means of the photoelastic effect. Accompanying acoustic emission, first detected by ear, was quantitatively measured with a piezoelectric transducer and a suitable filtering and amplification system. Synchronized sound cinematography has been used to correlate the acoustic emission with visual observation of twinning. The resultant motion picture has been used to determine the stress levels required for twinning in Brazilian quartz and to set limits on the twin wall velocity. The possible relevance to rock noise and earthquake precursory phenomena is discussed.