This is a Sasanian seal, likely made of agate, dating from around the 3rd century. Seals are small carvings used to create impressions on clay or other materials, and were used to denote ownership through their designs. Influenced by the widespread use of seals in Greece from before the Common Era, the ancient Roman era saw the engraving of images of gods and people on seals. Although there are some adhering materials, a creature-like figure is clearly carved within the small space of about 20mm. A small hole for wearing it is also present. Stamp seals from the Persian Sasanian dynasty are mostly characterized by their dome shape, with a hole drilled through them for a string to be passed through for carrying. Many feature simple lines or plant-like patterns, and depictions of people and animals are relatively rare. This one appears to be a divine beast.