Onicrium

Onicrium (pronounced /əʊnɪcriːʌm/), also known as Shadowcross, as well as Hissing Ore or Fe't'ek Yiss by it's founders, was a volatile crystal native to the underground caves of the forest planet Del'k'aa, and utilized by the B'l Akzic people as ammunition for their weapons. It was well-known for it's destructive potential, it's surface melting and fizzling away most other substances upon contact, most notably flesh or metallic compounds. A single, slim dart of the material was able to progressively burn up to a sixteen-centimeter hole in flesh, the agonising process taking roughly twenty seconds. Removing the source would considerably dull the effects, but the acid would still burn for a time. Contact with Onicrium anywhere near any vital points was nearly always fatal, and this fact greatly aided the B'l Akzic in the Siege of Del'k'aa.

Coincidentally, the bark of a tree from Del'k'aa, the very place where the ore originates, was completely immune to the material's effects, allowing handling of the material by the B'l Akzic, though this fact was never shared with any other species. Due to the declined alliance between Del'k'aa and the Sentinels as well as the repelling of the Zealots, Onicrium has not been mined for galaxy-wide use and is very rare off of its home planet.