In the "Star Trek" fictional TV and movie franchise, dilithium crystals are a material that serves as a controlling agent in the faster than light warp drive of the Starship Enterprise. It fuels the ship. In the original 1966 - 69 TV series, these crystals are called rare minerals and can not be replicated. The search for these minerals become a recurring plot element in many of the TV episodes.

Later in the franchise, a periodic table is shown during a "Star Trek: The Next Generation" episode. The chemical symbol, Dt and the atomic number 87 present the element (dilithium). In reality these items belong to the element francium, and dilithium (Li2) is in fact a molecule composed of two covalently bonded lithium atoms.

In "Star Trek", dilithium is depicted as an extremely hard crystalline mineral. It occurs naturally on some planets, moons, and asteroids in the universe. When placed in a high frequency electromagnetic field, eddy currents are induced in its structure which keep charged particles away from the crystal lattice. This prevents it from reacting with antimatter when energized. Because the antimatter particles never actually touch the dilithium, it can be used to contain and regulate the annihilation reaction in a starship's warp core. All required steps are taken to prevent a ship's uncontrolled annihilation reaction explosion. During the series, dilithium would obey known laws of molecular physics which allow it to be used as fusion fuel.

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