Magatama are curved, comma-shaped beads that appeared in prehistoric Japan from the Final Jōmon period through the Kofun period, approximately ca. 1000 BCE to the sixth century CE. The beads, also described as "jewels", were made of primitive stone and earthen materials in the early period, but by the end of the Kofun period were made almost exclusively of jade. Magatama originally served as decorative jewelry, but by the end of the Kofun period functioned as ceremonial and religious objects.

(Source: Wikipedia)