The three jewels in J.R.R. Tolkien’s legendarium are called the Silmarils. Fëanor, the greatest craftsman among the Elves, made them during the Years of the Trees before the First Age.
The jewels contained the light of the Two Trees of Valinor, Telperion and Laurelin. Their beauty made them objects of desire, and Morgoth stole them after destroying the Trees. Fëanor and his sons then swore an oath to recover them, a decision that drove much of the tragedy described in The Silmarillion.
The Silmarils are not the same as the Rings of Power or the palantíri. The Rings are magical rings associated with Sauron’s plan of domination, while the palantíri are seeing-stones. The Silmarils belong to the much earlier mythology of the First Age and remain central to Tolkien’s account of Elvish history.