The crystal is a piezoelectric component that has resonance at a particular frequency. It is usually driven by an active oscillator circuit. The crystal determines the frequency, but does not create it.
Oscillator integrated the clock generator IC & the crystal in a ceramic bady, and it have the best performance than crystal, such as jitter, rise time, fall time, duty cycle... But the oscillator is very expensive, it worth 7-10 times crystal!