An unstable radiolytic substance refined by the Xindi for their planet-destroying weapon in Enterprise, and smuggled by Quark aboard his shuttle in Deep Space Nine's Little Green Men.
Kemocite is a hazardous, highly energetic compound with a distinctive radiation signature. It is useful in weapons and power systems and is strictly controlled in the Federation of the 24th century.
In Enterprise it is a key ingredient of the Xindi superweapon. In The Shipment, set in 2153, Archer traces a kemocite signature to a refinery run by the Xindi-Arboreal Gralik, who had not known what his product was for and helps Archer sabotage and track a consignment.
The substance returns in the Deep Space Nine episode Little Green Men. Quark hides a contraband load of kemocite in the shuttle he takes to Earth; an accident involving it throws the ship back to Roswell in 1947, and Rom uses what remains to get the Ferengi home.