Silithium is a material found in comets.
In 2371, a comet in the Gamma Quadrant containing silithium was drawn towards the Bajoran wormhole. Benjamin Sisko and Kira Nerys stopped the silithium comet from collapsing the wormhole by shielding the comet with the shields of a shuttlepod. Some silithium leaked out, allowing communications through the wormhole. (DS9 episode: "Destiny")