Adhesion and charging of quartz surfaces

Very large charges are obtained from the light contact of two crystal faces of quartz with each other, an X cut face being positive with respect to a Z cut. The effect is not piezoelectric in origin, since it does not reverse when an X_ face is used instead of an X+. The not inconsiderable charges obtained using vitreous silica may be due to patches of incipient crystallization. The tendency of well-cleaned quartz and silica surfaces to adhere seems not to affect the charging, and the adhesion is not electrical in origin. It is unlikely that electrostatic forces ever contribute appreciably to the force of friction.