In the Star Trek fictional universe, dilithium is a fictional material that serves as a controlling agent in the matter-antimatter reactors. In the original series, dilithium crystals were rare and could not be replicated, making the search for them a recurring plot element. According to a periodic table shown during a Next Generation episode, it has the atomic number 87 (which in reality belongs to francium), and the chemical symbol Dt.[1]
In reality, dilithium (Li2) is a molecule composed of two covalently bonded lithium atoms which exists naturally in gaseous lithium.
Dilithium is depicted as a valuable, extremely hard crystalline mineral that occurs naturally on some planets.