Crystals as RLC circuit? How?
The crystal doesn't physically behave like an inductor, but it has a very precise frequency at which its response is resonating, similarly to an RCL network.

From Wikipedia:


  When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric field by applying a voltage to an electrode near or on the crystal. This property is known as electrostriction or inverse piezoelectricity. When the field is removed, the quartz will generate an electric field as it returns to its previous shape, and this can generate a voltage. The result is that a quartz crystal behaves like a circuit composed of an inductor, capacitor and resistor, with a precise resonant frequency. (See RLC circuit.)


So, piezoelectricity is used to create a mechanical strain on the crystal, which tends to return to the original position, generating a voltage for the same principle. When this happens at the resonant frequency the oscillation will happen at the maximum amplitude.

The advantage of crystal oscillators is that the resonant frequency depends on the geometrical properties of the crystal plate, and is therefore very stable in temperature.