Why The Pierce oscillator is essentially a Colpitts topology in which the inductive element is replaced by a quartz crystal operating slightly above its series resonance, where it looks inductive. The crystal sits between the output and input of the amplifying device (drain to gate, or collector to base) and returns the in-phase energy needed to sustain oscillation. Because the crystal's very high Q sets the loop phase, the Pierce is both simple and very frequency stable.
Watch out The tapped coil answer describes a Hartley oscillator, where an inductive divider provides the feedback; a capacitive divider would make it a Colpitts, and link coupling suggests an Armstrong or tickler-coil design.
Learn the feedback family: Hartley = tapped coil, Colpitts = capacitor divider, Pierce = crystal, Armstrong = transformer.