Piezoelectric Effects in Rocks

Abstract

Theoretical consideration of the symmetry of piezoelectric aggregates of quartz, of quartz-bearing rocks and of rocks which contain nepheline and tourmaline have permitted us to hypothesize the existence of a piezoelectric effect in such rocks. However, this does not assure that they do exist. The presence of a piezoelectric effect in a rock, as indicated earlier, requires a specific orientation of the polar (electrical) axes of the mineral grains. While the orientation of the optical axes of quartz grains may be studied in thin section using a polarizing microscope, there is no method which permits determination of the orientation of the electrical axes in thin sections. We include under physical orientation of the axes of mineral grains such forms of orientation as those in which the polar axes are consistently distributed with orientations parallel to a common plane. Evidence on the geometric orientation of the electrical axes of quartz grains may be obtained for a few classes of rocks by x-ray diffraction methods. Positive results may be obtained by this method only in cases in which rocks are monomineralic fine-grained aggregates with a high degree of orientation of the crystallographic axes.