This necklace features a shell that looks like an eye! Eye motifs are believed to protect against the evil eye and malice. There are no markings on the main body, and the material is unknown. There is some engraving on the chain, but it is unreadable. It is probably "NS" and appears to be silver plated. The length is approximately 45cm. The third photo is a size comparison with a 500-yen coin.