Crysknife

A crysknife is a fictional weapon in the Dune universe created by Frank Herbert. According to the 1965 novel Dune, it is made from the crystal tooth of Shai'Hulud, the giant sandworms that live below the sands of the desert planet Arrakis.

A crysknife is the formal and sacred weapon of the planet's native Fremen. It is a milk-white, double-edged curved knife, the blade about 20 centimeters long. The crysknife comes in two forms, fixed and unfixed. Unfixed knives need to be stored in proximity to an electrical field produced by the human body or they will disintegrate after a period of time. Fixed crysknives are put through chemical processes to keep them permanently intact. In Children of Dune, Leto Atreides II notes that "The crysknife dissolves at the death of its owner."

All young Fremen must go through a ritual confirming their adulthood, which is sealed with the gift of a crysknife to the adolescent warrior. According to the religious beliefs of the Fremen, a crysknife must draw blood each time it is unsheathed before being sheathed again. The Fremen also forbid outsiders from possessing crysknives, and in Dune Lady Jessica refers to "the fabled crysknife of Arrakis, the blade that had never been taken off the planet, and was known only by rumor and wild gossip." When the Shadout Mapes gives one to Jessica, the Fremen woman warns, "Who sees that knife must be cleansed or slain!" When two Fremen meet in combat, one will often taunt the other by saying, "May thy knife chip and shatter."

The Legends of Dune prequel trilogy (2002–2004) by Brian Herbert and Kevin J. Anderson establishes that Selim Wormrider is the first to use a crysknife, during the events of the Butlerian Jihad.