Quartz crystal belong to triangle system.

The natural quartz crystal has shape of hexagonal prism with a pyramid attached to each end. It has to be cut in particular direction & taken as a thin slab to fabricate the transducer. The line joining the two end points is called optic axis or Z axis. Clearly, the section of crystal at right angles to Z-axis is hexagon. A quartz crystal has three axes which are explained below –

(a)

(b)

(c)