Elas

From Memory Alpha, the free Star Trek reference.

Elas is the homeworld of the Elasian people, located in the Tellun system. Elas occupies an orbit inward from its neighbor, the planet Troyius.

Dilithium crystals were abundant on the planet, where it was considered to be a rather common stone. The Klingon Empire became aware of the Elasian dilithium deposits by 2268, and held the secret closely while they argued with the Federation over jurisdiction of the Tellun system. (TOS: "Elaan of Troyius")