In J.R.R. Tolkien’s mythology, what are the jewels called the Silmarils made from?

In J.R.R. Tolkien’s mythology, the Silmarils contain the light of the Two Trees of Valinor.

The Silmarils are three extraordinary jewels created by Fëanor, the greatest craftsman among the Noldor. He captured within them the blended light of Telperion and Laurelin, the Two Trees that illuminated Valinor before the creation of the Sun and Moon. Their beauty and sacred radiance made them the most prized objects in the Elder Days.

After the Dark Lord Morgoth destroyed the Two Trees and stole the jewels, Fëanor and his sons swore an oath to recover them. That oath drives much of the tragic history told in The Silmarillion. The Silmarils are not ordinary gemstones and are not made from mithril, another famous substance in Tolkien’s legendarium. Their power comes from the light they preserve, while their story concerns pride, kinship, oath-breaking, and the devastating consequences of possession.