The tube-shaped ritual jade object called a cong first appeared in northeast China in the Neolithic period, circa 4000–2100 B.C. Although the precise ceremonial use of the cong is unknown, writers in the late Zhou dynasty described the cong as a symbol of the Earth, pairing it with the ritual disk called a bi, which was thought to symbolize Heaven. Cong are rare after the Neolithic period, although they were sometimes rediscovered in the Shang and Zhou dynasties and cherished as ancient objects. Unlike many highly decorated cong tubes from the south-central Chinese Liangzhu culture, this cong is very simple in form, with an undecorated surface. The style and the dark, almost black jade associate it with jades from the Longshan culture in China's Shaanxi province dated to approximately 2500-1700 B.C.