In the radio world we use the quartz crystal to construct a crystal oscillator. The vibrating crystal generates a sinusoidal electronic signal on a precise frequency.
The modern radio receiver uses a 10 MHz quartz crystal as a reference for the frequency synthesizer for the tuned frequency.
Crystals must be custom tuned by cutting or grinding to exact dimensions and tolerances to achieve a highly accurate desired frequency.
Crystals age over time and cause the frequency to drift from the original design.
Because a crystal can operate at either its series or parallel resonance frequencies a crystal oscillator circuit needs to be tuned to one or the other frequency as you cannot use both together.
A quartz crystal can act as either a capacitor, an inductor, a series resonance circuit or as a parallel resonance circuit.
identification
Crystals marked P-77 are for radio shack scanner with 10.7 IF