This is used in piezo-electric gas lighters. If an alternating current is applied to the crystal it oscillates. This is used in controlling radio wavelengths, usually using synthetic quartz. Quartz watches use these properties. Silicon chips depend upon the directional crystal properties to function.
Electrical current is conducted better in some gemstones than others.
Natural blue diamonds conduct electricity while the irradiated blue ones do not. A simple circuit can be constructed to test this. The is the tendency of a crystallized mineral to break in definite directions related to the crystal structure producing relatively smooth cleavage break surfaces. Cleavage planes are always parallel to a particular cleavage face, i.e. diamond cleaves in any of the four directions parallel to the faces of the octahedron. Almost all crystals have a tendency to cleave.