Verdenicine gas was a rare, naturally occurring toxic substance which could be found underground on certain Class M planets. It did not show up on scans made by a standard Starfleet tricorder of the early 25th Century, but did react visibly with oxygen to form a green dust, which was explosive and could be ignited by phaser fire. Verdenicine gas could be used as a primitive way of transferring power.
Verdenicine gas was abundant on the planet Yamatai, and in the early 25th Century the Solarii cultists living on the planet used a network of verdenicine gas taps as a makeshift power source for their scavenged technology. This network proved to be a liability when Starfleet crash survivors set off an explosion within the network at the main Solarii base while attempting to escape the cultists. This caused a chain reaction which destroyed much of the Solarii compound. (Star Trek Online: Valkyries: "Survivors of Yamatai")