Nitrium

From Memory Alpha, the free Star Trek reference.

Nitrium is a metallic element or alloy prevalent in asteroids and widely used in the construction of Federation starships. Nitrium was present in most ship's systems, notably on the Galaxy-class of vessels where the substance was present in life support systems, computers, and engines.

Nitrium is also present in large amounts in dilithium chambers. The presence of nitrium in these critical areas created a vulnerability for the USS Enterprise-D in 2368 when it encountered a nitrium parasite that began to metabolize the nitrium on board and threatened to cripple the ship. (TNG: "Cost of Living")