Chrondite
From Star Trek : Freedom's Wiki
Chrondite is a metallic alloy or element that is present in significant quantities in some asteroids. It is a dense, durable metal, especially when combined with Nitrium.
In 2368, an asteroid with a core of chrondite and nitrium threatened the planet Tessen III. The strong, dense core rendered the asteroid partially invulnerable to Photon Torpedoes, so it could only be destroyed by a concentrated particle beam. (TNG: "Cost of Living")
