Word of the Day: Silmaril – the three jewels made by Fëanor, as his heart was bound to the things he made. It was also made before the destruction of the Two Trees of Valinor, filled with their light.
They were gems of immense beauty, and crafted of silima, a hard crystalline substance. After this, Melkor started to have a lust for them in which remembering its radiance caused a fire in his heart (The Silmarillion).
Later, the Valar knew that the Men and the Elves were coming. However, they didn’t know about it as Manwë didn’t reveal it to them. Then, they asked Fëanor to give up the silmarils. He refused.
One day, Fëanor was upset at Morgoth as he found out that his father Finwë was killed by Melkor, while subsequently stealing all the gems. Fëanor would not stop fighting until the gems were recovered, but it caused a long grief of the Elves and Men.
Eventually, Thingol knew of these gems from the Noldor, and asked Beren to capture one of them for his daughter Luthien. Beren went to Angband, in great peril but eventually recovered one jewel, but it was swallowed by Carcharoth. After he was slain by the hallowed light, the jewel was finally delivered to Thingol.