Effect of crystal orientation on lapping and polishing processes of natural quartz

Lapping and polishing processes of natural quartz are investigated in relation to crystallographic orientation and applied normal stress. Weight loss measurements and surface profilometry were carried out in X-, Y-, Z-, and AT-cut samples. The relationship found between material removal rate and stress depends on specimen orientation. Based on indentation fracture mechanics, this behavior is discussed in relation to fracture toughness and scratch hardness anisotropy of quartz crystals. Scanning electron microscopy (SEM) shows that brittle microcracking is the primary mechanism involved with material removal in the lapping process. Plastic deformation mechanisms begin to operate on lapped and polished surfaces above a certain value of stress. Surface profiles and SEM micrographs show that the roughness of lapped surfaces decreases with increasing normal stress, but an opposite behavior is observed in polished surfaces.