Nimphelos

The great pearl from the Falas-elves ( Círdans people ) which was a great part of the prize for the Dwarves of Belegost who builded Menegroth for Thingol and Melian in Doriath. The pearl had a size of a pigeon-egg and shone like starlight on the waves of the sea. From the coasts and shallow waters in the Bay of Balar Círdan and his folks gathered great stores of pearls and of these many was given, or traded perhaps, into the hands of Thingol. These kind of gems the Dwarves had never seen and they prized them highly.

Valian Years of the Trees.

V.Y.t.1300 - 1350. Thingol had by foresight and counsel of Melian sought the aid and craft of the Dwarves of Belegost to make him a strong place to dwell and Menegroth was delved. The payment was, besides knowledge Melian taught them, the pearl Nimphelos.