Duridium was a type of ore.
On stardate 48960.9 the Xhosa hauled a load of duridium ore to Solais V. The ship was due to return to Deep Space 9 the following month. (DS9: "The Adversary")
In 2373, a Changeling posing as Doctor Julian Bashir claimed to O'Brien that he had ordered two sets of new duridium alloy darts that he had told him about. (DS9: "By Inferno's Light")
Refined duridium is used in the construction of barrels, and is resistant to Jem'Hadar polaron rifles. (DS9: "Blaze of Glory")