James Watt opinion 11/6/1987: Neolithic. Real ones are circular inside, with outside of rounded square form. Fakes are rounded outside.
A ‘cong’ is a jade cylinder that is square on the outside with a round perforation in the middle. The outside walls are usually divided into sections by horizontal cuts in the four corners. The height of ‘cong’ varies drastically, ranging from 49 cm to a mere 3 cm. Tall ‘cong’ were definitely more difficult to make than short ones.
An ancient Chinese text called 'The Rites of Zhou' states that the ‘cong’ was used as a sacrifice to the earth. Archaeology has revealed that ‘cong’ served a ritual function in Neolithic times.