What is the name of the powerful jewel central to Tolkien’s First Age mythology?

The powerful jewels central to J.R.R. Tolkien’s First Age mythology are the Silmarils.

The Silmarils were three radiant jewels created by Fëanor, an exceptionally skilled Noldorin Elf. They contained the light of the Two Trees of Valinor, making them far more significant than ordinary precious stones. The Dark Lord Morgoth stole them, and the resulting oath and wars shaped much of the history told in The Silmarillion.

The Silmarils are sometimes confused with the Arkenstone, the jewel discovered beneath the Lonely Mountain in The Hobbit. The Arkenstone is important to the Dwarves of Erebor, but it is not one of the Silmarils. The Rings of Power belong to a later period of Middle-earth’s history and have a different origin.

Tolkien used the jewels to connect personal ambition with vast historical consequences. Fëanor’s possessiveness, the oath sworn by his sons, and the long struggle against Morgoth all show how beauty and craftsmanship can become sources of conflict when treated as objects to own at any cost.