In J.R.R. Tolkien’s mythology, what were the three jewels made by Fëanor called?

The three jewels made by Fëanor in J.R.R. Tolkien’s mythology were called the Silmarils.

The Silmarils were jewels created by Fëanor, the greatest craftsman among the Ñoldor. They contained the light of the Two Trees of Valinor, Telperion and Laurelin, and became the central objects of desire and conflict in much of The Silmarillion.

After Morgoth stole the jewels and carried them to Middle-earth, Fëanor and his sons swore an oath to recover them. That oath drove many later events, including wars among Elves and their conflicts with Morgoth. The three Silmarils ultimately passed through several tragic episodes involving Beren and Lúthien, Eärendil, and the sons of Fëanor.

The Silmarils are not the same as the Rings of Power or the palantíri. The Rings were made in a later historical context, while the palantíri were seeing-stones associated with Númenor and Middle-earth.