Small stone/jade white cong. A similar object found in a tomb in China is described as follows: "First used in the Neolithic Period. Ancient Chinese believe that the sky envelops the square ground like a lid. The shape of Cong follows such opinion. Its outer edge is square and the inner edge is rounded. In the ancient ceremonies, Bi was used to offer sacrifice to the heaven while Cong to the earth. " (https://artsandculture.google.com/asset/jade-cong-with-patterns-of-animal-face/3QEN-Bi0MlltfQ)