Chinese jade form found in the Shang (c. 1600–1046 BC) and Zhou (1046–256 BC) dynasties. It is a flat disk similar in shape to the bi, except that the outer edge is broken into an irregular serration of major and minor projecting teeth, much like a circular saw blade. It has been suggested that the xuanji may have been used as an astronomical instrument to plot the location of the stars, possibly in conjunction with another jade object, the cong.