Yurium was a chemical compound with the chemical formula YU2. This compound was capable of storing large amounts of energy and was usually used as a an explosive.
Bela Tyken used anicium and yurium from his cargo to create a massive explosion. This kind of anomaly would later be named Tyken's Rift to his honor. (TNG: "Night Terrors")
In 2365, a planetary scan by the USS Enterprise-D detected 2% of yurium in the atmospheric composition of Theta VIII. (TNG: "The Royale")
-ium was used in chemistry to identify a metallic element.