This is a "Ganzen" (cicada), a type of burial item from the Han Dynasty, similar to the jade frog waist pendant also listed on this site. It is made of jade. It was placed in the mouth of the deceased, with the hope of resurrection. The size is approximately 2.1 cm x 0.8 cm. I displayed it in this condition myself, so I am offering it as is. If you don't need it, it's only attached with fishing line, so you can cut it off and remove it.