Kryptonite

Kryptonite is a radioactive Kryptonian mineral / meteor fragment.

It is a remnant of the exploded planet Krypton.

The only substance in the universe that can zap (Superman's) strength in he comes within 20 feet of it.

There are a wide variety of types of Kryptonite:

Green Kryptonite
Green Kryptonite, although rare, is the most common type. It is harmful to natives of the planet Krypton. If one is exposed long enough, they could go into a Kryptonian trance or it could kill them. Villains use Green K as a weapon to defeat Superman. Green K was a key element in Doctor Natas's Noxium crystal.

Red Kryptonite
Although Red K has no fatal effects on Kryptonians, it's effects are still unpredictable. It could give Superman extra arms, or it could even turn him into a child. It could do a ton of other things. Red K is unpredictable, there's no telling what may happen. But one thing about these unpredictable effects, is that they are only temporary, usually only lasting about a day.

Blue Kryptonite
Blue K isn't harmful to Kryptonians at all, in fact, when injured, it can heal them. However, it's effects on Bizarros (such as Bizarro himself) is deadly.

Gold Kryptonite
Gold K is capable of removing a Kryptonian's super powers permanently. There was only one known chunk in existence, and it was transformed into a bowling ball by Firestorm.

White Kryptonite
White Kryptonite is harmless to Kryptonians, but is lethal to most if not all plant life.

Krypton Steel
Krypton Steel is another form of Kryptonite, that is also presumably a very rare form. It's basically Krypton's version of the earth metal known as "steel." It's harmless to Kryptonians, but it's also indestructible to anything except for Superman, or possibly another equally powerful being. (Although this seems unlikely, since Solomon Grundy and Bizarro are both roughly the same strength as Superman, and yet they didn't even attempt to open a box made of Krypton steel. Instead the Legion tricked Superman into doing it for them)

=Episode Appearances=

More coming soon!
 * SF:The Menace of the White Dwarf (Green K)
 * Challenge of the SuperFriends: Batman: Dead or Alive
 * The Super Powers Team: Galactic Guardians: The Death of Superman (Green K)
 * new SuperFriends (1978): Terror from the Phantom Zone (Red K & Blue K)