how the crystal connected across the collector and base of a bjt pierce oscillator provide 180degree phase shift?

a normal oscillator will provide 360degree phase shift. of this 180degree is by the transistor amplifier and the remaining 180 is by the feedback circuit or tank circuit. but in the case of a pierce crystal oscillator ,it is the crystal which connected across the collector(output) and base provides 180degree phase shift the crystal provide 180degree phase ?