§ Of the Sindar The Silmarillion

Now Melian had much foresight, after the manner of the Maiar; and when the second age of the captivity of Melkor had passed, she counselled Thingol that the Peace of Arda would not last for ever. He took thought therefore how he should make for himself a kingly dwelling, and a place that should be strong, if evil were to awake again in Middle-earth; and he sought aid and counsel of the Dwarves of Belegost They gave it willingly, for they were unwearied in those days and eager for new works; and though the Dwarves ever demanded a price for all that they did, whether with delight or with toil, at this time they held themselves paid. For Melian taught them much that they were eager to learn, and Thingol rewarded them with many fair pearls. These Círdan gave to him, for they were got in great number in the shallow waters about the Isle of Balar; but the Naugrim had not before seen their like, and they held them dear. One there was as great as a dove's egg, and its sheen was as starlight on the foam of the sea; Nimphelos it was named, and the chieftain of the Dwarves of Belegost prized it above a mountain of wealth.