Nimphelos

Círdan's people gathered pearls out of the shallow water around the Isle of Balar in the Years of the Trees, and the whole take went to Thingol of Doriath. One of them was different enough to be given a name. Nimphelos was the size of a dove's egg, and it is the only pearl in the record with a name of its own. It did not stay in Doriath. When the Dwarves of Belegost finished the building of Menegroth and asked to be paid for the work, Thingol handed over Nimphelos along with a great quantity of the other pearls, and the Dwarves, who had never seen the like, held them dear. The Lord of Belegost counted Nimphelos the most valuable thing he owned.