In fact, quartz resonator is an analog of the oscillation circuit based on the capacitance and inductance.
How it works crystal based on the piezoelectric effect.
The basis of crystal is a quartz plate. Quartz - is one form of silica SiO2. The crystal is an electromechanical oscillation system. Any oscillation system has its own resonant frequency. In crystal also has a nominal resonant frequency. If a quartz plate attached to an AC voltage which coincides with the resonance frequency of the quartz plate, the resonance occurs and the amplitude of the oscillation frequency increases sharply.
Applications quartz crystals - a highly stable oscillator clock signal and the reference frequency, the circuit frequency selection, frequency synthesizers, etc.