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Kryptonite is a fictional material from the Superman mythos —the ore form of a radioactive element from Superman's home planet of Krypton. It is famous for being the ultimate natural weakness of Superman and most other Kryptonians, and the word Kryptonite has since become synonymous with an Achilles' heel —the one weakness of an otherwise invulnerable hero.^[1]

Originating in the Superman radio show series, the material is usually shown as having been created from the radioactive remains of Superman's native planet Krypton, and generally has detrimental effects on Superman and other Kryptonians. The name "kryptonite" covers a variety of forms of the substance, but usually refers to the most common "green" form.

A form of the fictional mineral "Kryptonite" has been discovered recently in Siberia; it has been formally named Jadarite (after the region where it was discovered). The composition of the mineral is sodium lithium boron silicate hydroxide, which is one element short of the description of Kryptonite in Superman Returns (the mineral lacks fluoride). The actual mineral is white and is harmless to humans.^[2]

Under standard chemical naming procedures, the -ite suffix of kryptonite would denote an oxyanion of the element krypton. However, krypton is a noble gas that forms compounds only with great difficulty, and such an oxyanion is not known. Nevertheless, the University of Leicester presented the Geological Society with krypton difluoride to commemorate the 70th anniversary of Superman.^[41]

In virtually all versions of the Superman mythos, kryptonite is described as having formed through a process of nuclear fusion attendant to the explosion which destroyed the planet Krypton. Some accounts describe the fusion process as a result of the planet-destroying explosion, others as the cause of it, but all agree that the majority of the debris of the planet was converted into kryptonite and propelled into interstellar space by the force of the explosion, with some ultimately reaching Earth and becoming a threat to Superman—and other Kryptonians.

The term kryptonite instead implies a meteorite from the planet Krypton, as in the Lois & Clark: The New Adventures of Superman episode "The Green, Green Glow of Home," where it is given as "periodic element 126", which in reality corresponds to unbihexium/eka-plutonium, the most stable of the elements in the so-called island of stability. Superman: The Man of Steel Sourcebook (1992), while non-canon, concurs, referring to kryptonite as "the common ore of the super-actinide kryptonium, an unusually stable transuranic element, whose atomic number is believed to be 126." Kryptonium is given a radioactive half-life of 250,000 years.

In Superman: The Movie, Lex Luthor describes Superman's enhanced Kryptonian physiology as being vulnerable to kryptonite's particular radioactive "signature". More recently, some issues of Superman indicate the mechanism by which green kryptonite may hurt Superman. Superman's cells absorb electromagnetic radiation from stars (like Earth's sun). Kryptonite's radioactivity interferes with this semi-photosynthetic process, driving the energy out of his cells in a painful fashion.

Some versions of the adverse effects of kryptonite describe the radiation as affecting the blood chemistry of the victim, causing accelerated effects similar to sickle cell anemia in terrestrial humans, and also causing the skin of the victim to turn green as exposure time increases.

Long-term exposure to kryptonite is said to have the same effects on terrestrial human beings as exposure to other radioactive materials; an extended storyline in the comics around 1990 involved Lex Luthor developing cancer from the kryptonite ring he kept on his finger.[edit]