A necklace of five hundred green-as-grass emeralds given to the Dwarves of Erebor by Girion, who was the last King of Dale before the attacks of Smaug.

The necklace was given in payment for a coat of mail, of pure silver, triple the strength and power of steel, that Girion had commissioned for his son. It became a part of the hoard of Smaug and disappeared from view until it was recovered from the Hoard after Smaug’s death in T.A.2941.

After the Battle of Five Armies the Emeralds of Girion were given to Bard the Bowman, as part of his fourteenth share of the Hoard. He in turn gave them to the Elvenking in reward for his assistance, after the destruction of Lake-Town and for his help in the Battle of Five Armies.
Encyclopedia entry originally written by PotbellyHairyfoot