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Kryptonite is a fictional element from the Superman comic book series.

Table of contents
1 Before Crisis on Infinite Earths
2 Post-Crisis
3 Depiction in Other Media
4 Afternotes

Before Crisis on Infinite Earths

Before the Superman mythos was redefined by writer John Byrne, the pre-Crisis DC Universe was home to a variety of elements called Kryptonite. Kryptonite was produced from the material of Superman's home planet Krypton, when it was destroyed in an explosion. Kryptonite is usually found in the form of a glowing green rock or metal, but crystalline forms have also made appearances (most notably Jewel Kryptonite, see below) along with different-colored variants such as red kryptonite. These different forms may represent multiple allotropes or isotopes of Kryptonite, or a more exotic variation in composition based on currently unknown particles.

Near the end of the run of the Pre-Crisis Superman, all known Kryptonite on Earth was transmuted into iron, but Kryptonite can be synthetically manufactured by a variety of unknown means and additional material left over from the destruction of Krypton continues to fall from space.

Kryptonite emits a radiation that has an adverse effect on Kryptonian natives such as Superman, though different varieties of kryptonite have different effects. It was assumed for a long time that Kryptonite radiation was harmless to non-Kryptonians, but occasional isolated incidents were reported where it had sporadic affects. Recently it has been clearly established that, while short-term exposure to Kryptonite is safe, long-term exposure over a period of months is likely to cause cancer. The billionaire industrialist and inventor Lex Luthor discovered this inadvertently after acquiring a ring with a green Kryptonite fragment set in it to provide protection against Superman's persecution. It is not known what the half-life of any of Kryptonite's forms is.

The 11 known forms of pre-Crisis Kryptonite


After the DC Comicbook universe event known as "Crisis on Infinite Earths" in 1985, the entire Superman mythos underwent a substantial retcon, rewriting Superman as more human and less invulnerable. Among the many changes were the properties of Kryptonite. In the post-Crisis universe, only one form of Kryptonite is naturally occurring: the green variety. It is a mildly radioactive element that was formed in the crust of the planet Krypton as the result of an ancient Kryptonian war. As millennia passed, the radiation from this mineral began to kill Kryptonians; it became known as the green plague. This eventually led to the planet's core becoming unstable, leading to the destruction of Krypton.

Some issues of Superman have indicated the mechanism by which Kryptonite hurts Superman; Superman in some ways is a living solar battery; his cells absorb electromagnetic radiation from yellow stars (like our Sun); Kryptonite's radioactivity interferes with this process, driving the energy out of his cells in a painful fashion. Long term and high-level exposure can be fatal to Superman. Long-term exposure of Kryptonite to human beings is known to have the same effect as exposure to Earth-borne radioactive materials. These effects include cancer, as Lex Luthor discovered.

It is speculated that kryptonite may be located in a hypothetical "island of stability" high on the periodic table, beyond the currently known unstable elements, in the vicinity of atomic number 150. The transmutation of Earth's Kryptonite could be explained by the acceleration of its natural atomic decay under this theory.

Depiction in Other Media

Most depictions of kryptonite in the various films and TV series of Superman have largely been limited to the Green varieties with occasional appearances of Red and Blue.

In the television series Smallville, the show expands on the concept of the substance being harmful to humans. On the show, not only is Green K harmful to Clark Kent, but it can produce bizarre changes in humans, typically turning them into powerful menaces that Clark must oppose.


Several sources have calculated the total mass of the planet Krypton based on the estimated mass of Kryptonite that fell to Earth, the assumption that the initial explosive distribution of pieces of Krypton was isotropic, and determinations of the mean distance between Krypton and Earth derived from certain passages in the Essene New Testament. The results are confusing at best, as the estimated mass of Krypton is 10**7 times the mass of our own sun, so a black hole was inevitable and the existence of corporeal life on the planet beforehand is questionable in the extreme. Further work on this topic continues.