Corzanium was an exotic material that existed within the galaxy.
It was noted as an extremely volatile substance that was only found within the maw of a black hole. The nature of Corzanium meant that it was strong enough to withstand powerful pressures such as those from a wormhole which made it the one building material that it was suitable in reinforcing the mouth of a verteron collider when attempting to create an artificial wormhole. This elements creation meant that it needed to be harvested on a quantum level with one particle at a time removed from the event horizon and recombined within the harvesting ships chambers.
The sequence of mining Corzanium involved a tractor beam, which lowered a mining probe into the black hole just above the event horizon. Once this was achieved, a bombardment of tachyon particles was initiated at the black hole, which charged the terms of probability and quantum steps the particles which were expelled in the process. This harvesting procedure was similar to drilling in a typical mining operation. As this occurred, the mining ship simply needed to guide the escaping matter into the mining probe with the tractor beam after which they beamed the probe onboard and put Corzanium into stasis.
In 2373, the Dominion sought to mine Corzanium from the Eye of Talek in Cardassian space in order to create an artificial wormhole that would connect them to their territories in the Gamma Quadrant. It was hoped that the use of the element would allow for the Founders to win the Dominion War. After the Federation discovered this plot, they dispatched an infiltration team led by Captain Jean-Luc Picard who worked with Ro Laren in order to sneak the Orb of Peace into Dominion space and destroy the vessel mining the Corzanium. (DS9 - The Dominion War novel: Behind Enemy Lines)