Defects in a rather perfect synthetic quartz crystal have been surveyed by x‐ray topography. Etching behavior and stress birefringence were also studied. The crystal, grown from az‐plate seed, contained Na and Al in concentrations of 50 ppm by weight. The crystal had grown in thecdirection with low dislocation density (∼ 3000 lines cm−2). The majority of dislocations made about 10° with thecaxis, only 15% had Burgers vectors with ac‐axis component. Cellular growth had developed as growth in thecdirection proceeded. The cell walls were identified with fault surfaces made visible by diffraction contrast. These surfaces were inclined at fairly small angles with [0001] and their intersections with (0001) formed an irregular polygonal network. Dislocations congregated in or near the fault surfaces in the later stages of growth. The fault surfaces outcropped at the grooves between protuberances on the rough external crystal surface of mean orientation (0001). The presence of fault fringes indicates impurity segregation in the cell walls: the fringe contrast could arise from a layer a few microns thick with a lattice parameter a few parts in 105different from that of surrounding material.