TOLKIEN HAD THE WORDS FOR IT: 16 THE QUENTA

In those far days Feanor began on a time a long and marvellous labour, and all his power and all his subtle magic he called upon, for he purposed to make a thing more fair than any of the Eldar yet had made, that should last beyond the end of all. Three jewels he made, and named them Silmarils. A living fire burned within them that was blended of the light of the Two Trees; of their own radiance they shone even in the dark; no mortal flesh impure could touch them, but was withered and was scorched. These jewels the Elves prized beyond all the works of their hands, and Manwe hallowed them, and Varda said: 'The fate of the Elves is locked herein, and the fate of many things beside.' The heart of Feanor was wound about the things he himself had made.

The Shaping of Middle-earth