Abstract
Longitudinal piezoelectric coefficients have been measured on cubic samples and from 150 different orientations on a spherical sample of coarse-grained vein quartz. The results are consistent with the presence of a piezoelectric fabric. The piezoelectric pole figure of the studied spherical sample demonstrates three distinct patterns of alternatively positive and negative signs defining one strong and two weak electric dipoles in the fabric. The magnitude of the piezoelectric effect along the major maximum is as large as 7% of the theoretical effect in a single crystal and is considerably higher than the expected statistical effect. Preferred orientation of the a-axes, was independently confirmed by subjecting the same spherical sample to neutron diffraction analysis. The location of nonpolar a-axes maximum determined by neutron diffraction analysis agrees with the piezoelectric maximum which is theoretically related to the polar preferred orientation of a-axes. The piezoelectric effect and neutron diffraction are both volume events and ensure reliable statistics for analysis of coarse-grained quartz aggregates where surface events (such as X-ray diffraction) may suffer poor statistics.