Thalmerite was a highly explosive compound capable of destroying starships in sufficient quantities.
The Klingon vessel IKS Toh'Kaht was destroyed by a thalmerite explosive device that Hon-Tihl placed near its reactor core shortly after its passage through the Bajoran wormhole. (DS9: "Dramatis Personae")
In 2371, the USS Voyager placed forty tons of thalmerite in a shuttlecraft prior to its anticipated capture by a Numiri patrol vessel. Captain Kathryn Janeway threatened to detonate the explosive which would have destroyed the shuttle and Numiri vessel unless the shuttle was immediately released. (VOY: "Ex Post Facto")